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ALGORITHMS1
Reference Manual
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Kurzweil K2500, ALGORITHMS1, KDFX Reference Manual

A lgorithm Reference
Part Number: 910319 Rev. A
FXAlg #1: MiniVerb ¥ FXAlg #2: Dual MiniVerb
FXAlg #1: MiniVerb ¥ FXAlg #2: Dual MiniVerb
Versatile, small stereo and dual mono reverbs
Allocation Units: 1 for MiniVerb, 2 for Dual MiniVerb
MiniVerb is a versatile stereo reverb which is found in many combination algorithms, but is equally useful on its own because of its small size. The main control for this effect is the Room Type parameter. Room Type changes the structure of the algorithm to simulate many carefully crafted room types and sizes. Spaces characterized as booths, small rooms, chambers, halls and large spaces can be selected.
Dry
L Input
R Input
Each Room Type incorporates different diffusion, room size and reverb density settings. The Room Types were designed to sound best when Diff Scale, Size Scale and Density are set to the default values of 1.00x. If you want a reverb to sound perfect immediately, set the Diff Scale, Size Scale and Density parameters to 1.00x, pick a Room Type and youÕll be on the way to a great sounding reverb. But if you want to experiment with new reverb flavors, changing the scaling parameters away from 1.00x can cause a subtle (or drastic!) coloring of the carefully crafted Room Types.
Diffusion characterizes how the reverb spreads the early reflections out in time. At very low settings of Diff Scale, the early reflections start to sound quite discrete, and at higher settings the early reflections are seamless. Density controls how tightly the early reflections are packed in time. Low Density settings have the early reflections grouped close together, and higher values spread the reflections for a smoother reverb.
L PreDelay
Miniverb
Core
R PreDelay
Dry
Simplified block diagram of MiniVerb
L Output
Wet Out Gain
R Output
Algorithm Reference-2
FXAlg #1: MiniVerb ¥ FXAlg #2: Dual MiniVerb
L Input
R Input
Dry
MiniVerb Balance
MiniVerb
Dry
Wet
Wet
Pan
L Output
Balance
R Output
Pan
Simplified block diagram of Dual MiniVerb
Dual MiniVerb has a full MiniVerb, including Wet/Dry, Pre Delay and Out Gain controls, dedicated to each of the left and right channels. The two blocks in the diagram above labeled ÒMiniVerbÓ contain a complete copy of the MiniVerb on the previous page. Dual MiniVerb gives you independent reverbs on both channels which has obvious benefits for mono material. With stereo material, any panning or image placement can be maintained, even in the reverb tails. This is pretty unusual behavior for a reverb, since even real halls will rapidly delocalize acoustic images in the reverberance. Since maintaining image placement in the reverberation is so unusual, you will have to carefully consider whether it is appropriate for your particular situation. To use Dual MiniVerb to maintain stereo signals in this manner, set the reverb parameters for both channels to the same values. The Dry Pan and Wet Bal parameters should be fully left (-100%) for the left MiniVerb and fully right (100%) for the right MiniVerb.
Parameters (MiniVerb):
PAGE 1
Wet/Dry 0 to 100%wet Out Gain Off, -79.0 to 24.0 dB
Rvrb Time 0.5 to 30.0 s, Inf HF Damping 16 to 25088 Hz
L Pre Dly 0 to 620 ms R Pre Dly 0 to 620 ms
PAGE 2
Room Type Hall1 Diff Scale 0.00 to 2.00x
Size Scale 0.00 to 4.00x
Density 0.00 to 4.00x
Algorithm Reference-3
FXAlg #1: MiniVerb ¥ FXAlg #2: Dual MiniVerb
Parameters (Dual MiniVerb):
PAGE 1
L Wet/Dry 0 to 100%wet R Wet/Dry 0 to 100%wet
L Out Gain Off, -79.0 to 24.0 dB R Out Gain Off, -79.0 to 24.0 dB
L Wet Bal -100 to 100% R Wet Bal -100 to 100%
L Dry Pan -100 to 100% R Dry Pan -100 to 100%
PAGE 2
L RoomType Hall1
L RvrbTime 0.5 to 30.0 s, Inf
L Diff Scl 0.00 to 2.00x L Density 0.00 to 4.00x
L Size Scl 0.00 to 4.00x L HF Damp 16 to 25088 Hz
L PreDlyL 0 to 620 ms L PreDlyR 0 to 620 ms
PAGE 3
R RoomType Hall1
R RvrbTime 0.5 to 30.0 s, Inf
R Diff Scl 0.00 to 2.00x R Density 0.00 to 4.00x
R Size Scl 0.00 to 4.00x R HF Damp 16 to 25088 Hz
R PreDlyL 0 to 620 ms R PreDlyR 0 to 620 ms
Wet/Dry A simple mix of the reverb sound with the dry sound.
Out Gain The overall gain or amplitude at the output of the effect.
Rvrb Time The reverb time displayed is accurate for normal settings of the other parameters (HF
Damping = 25088kHz, and Diff Scale, Room Scale and Density = 1.00x). Changing Rvrb Time to Inf creates an inÞnitely sustaining reverb.
HF Damping Reduces high-frequency components of the reverb above the displayed cutoff frequency.
Removing higher reverb frequencies can often make rooms sound more natural.
L/R Pre Dly The delay between the start of a sound and the output of the Þrst reverb reßections from
that sound. Longer pre-delays can help make larger spaces sound more realistic. Longer times can also help improve the clarity of a mix by separating the reverb signal from the dry signal, so the dry signal is not obscured. Likewise, the wet signal will be more audible if delayed, and thus you can get by with a dryer mix while maintaining the same subjective wet/dry level.
Room Type Changes the conÞguration of the reverb algorithm to simulate a wide array of carefully
designed room types and sizes. This parameter effectively allows you to have several different reverb algorithms only a parameter change away. Smaller Room Types will sound best with shorter Rvrb Times, and vice versa. (Note that since this parameter changes the structure of the reverb algorithm, you donÕt want to assign it a KDFX Modulation that will change it in real time.)
Diff Scale A multiplier which affects the diffusion of the reverb. At 1.00x, the diffusion will be the
normal, carefully-adjusted amount for the current Room Type. Altering this parameter will change the diffusion from the preset amount.
Algorithm Reference-4
FXAlg #1: MiniVerb ¥ FXAlg #2: Dual MiniVerb
Size Scale A multiplier which changes the size of the current room. At 1.00x, the room will be the
normal, carefully-tweaked size of the current Room Type. Altering this parameter will change the size of the room, and thus will cause a subtle coloration of the reverb (since the roomÕs dimensions are changing).
Density A multiplier which affects the density of the reverb. At 1.00x, the room density will be
the normal, carefully-set amount for the current Room Type. Altering this parameter will change the density of the reverb, which may color the room slightly.
Wet Bal In Dual MiniVerb, two mono signals (left and right) are fed into two separate stereo
reverbs. If you center the wet balance (0%), the left and right outputs of the reverb will be sent to the Þnal output in equal amounts. This will add a sense of spaciousness.
Algorithm Reference-5
FXAlg #3: Gated MiniVerb
FXAlg #3: Gated MiniVerb
A reverb and gate in series
Allocation Units: 2
This algorithm is a small reverb followed by a gate. The main control for the reverb is the Room Type parameter. Room Type changes the structure of the algorithm to simulate many carefully crafted room types and sizes. Spaces characterized as booths, small rooms, chambers, halls and large spaces can be selected. See the previous section (FXAlg #1-2) for details on the reverb.
The gate turns the output of the reverb on and off based on the amplitude of the input signal. One or both input channels is used to control whether the switch is on (gate is open) or off (gate is closed). This on/off control is called Òside chainÓ processing. You select which of the two input channels or both is used for side chain processing. When you select both channels, the sum of the left and right input amplitudes is used.
The gate is opened when the side chain amplitude rises above a level that you specify with the Threshold parameter. The gate will stay open for as long as the side chain signal is above the threshold. When the signal drops below the threshold, the gate will remain open for the time set by the Gate Time parameter. At the end of the Gate Time, the gate closes. When the signal rises above threshold, it opens again. What is happening is that the gate timer is being constantly retriggered while the signal is above threshold.
1
0
attack
time
signal rises
above threshold
If Gate Duck is turned on, then the behavior of the gate is reversed. The gate is open while the side chain signal is below threshold, and it closes when the signal rises above threshold.
signal falls
below threshold
gate time
Gate Behavior
release
time
If the gate opened and closed instantaneously, you would hear a large digital click, like a big knife switch was being thrown. Obviously thatÕs not a good idea, so Gate Atk (attack) and Gate Rel (release) parameters are used to set the times for the gate to open and close. More precisely, depending on whether Gate Duck is off or on, Gate Atk sets how fast the gate opens or closes when the side chain signal rises above the threshold. The Gate Rel sets how fast the gate closes or opens after the gate timer has elapsed.
The Signal Dly parameter delays the signal being gated, but does not delay the side chain signal. By delaying the main signal relative to the side chain signal, you can open the gate just before the main signal rises above threshold. ItÕs a little like being able to pick up the telephone before it rings!
Algorithm Reference-6
FXAlg #3: Gated MiniVerb
Parameters:
PAGE 1
Wet/Dry 0 to 100%wet Out Gain Off, -79.0 to 24.0 dB
Rvrb Time 0.5 to 30.0s, Inf HF Damping 16 to 25088 Hz
L Pre Dly 0 to 620ms R Pre Dly 0 to 620 ms
PAGE 2
Room Type Hall1 Diff Scale 0.00 to 2.00x
Size Scale 0.00 to 4.00x
Density 0.00 to 4.00x
PAGE 3
Gate Thres -79.0 to 0.0 dB Gate Time 0 to 3000 ms
Gate Duck In or Out Gate Atk 0.0 to 228.0 ms
Gate Rel 0 to 3000 ms
GateSigDly 0.0 to 25.0 ms
Reduction
-dB 60 40 * 16 * 8 4 0
Wet/Dry A simple mix of the reverb sound with the dry sound. When set fully dry (0%), the gate
is still active.
Out Gain An overall level control of the effectÕs output (applied after the gate).
Gate Thres The input signal level in dB required to open the gate (or close the gate if Gate Duck is
on).
Gate Duck When set to ÒOffÓ, the gate opens when the signal rises above threshold and closes when
the gate time expires. When set to ÒOnÓ, the gate closes when the signal rises above threshold and opens when the gate time expires.
Gate Time The time in seconds that the gate will stay fully on after the signal envelope rises above
threshold. The gate timer is started or restarted whenever the signal envelope rises above threshold.
Gate Atk The attack time for the gate to ramp from closed to open (reverse if Gate Duck is on)
after the signal rises above threshold.
Gate Rel The release time for the gate to ramp from open to closed (reverse if Gate Duck is on)
after the gate timer has elapsed.
Signal Dly The delay in milliseconds (ms) of the reverb input signal relative to the side chain signal.
By delaying the reverb signal, the gate can be opened before the reverb signal rises above the gating threshold.
For descriptions of the other parameters, see the previous section, FXAlgs #1-2.
Algorithm Reference-7
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
FXAlg #4: Classic Place FXAlg #5: Classic Verb FXAlg #6: TQ Place FXAlg #7: TQ Verb FXAlg #8: Diffuse Place FXAlg #9: Diffuse Verb FXAlg #10: OmniPlace FXAlg #11: OmniVerb
More Complex Reverb algorithms
Allocation Units: ÒClassicÓ 2; others 3
This set of 2 and 3 PAU sized algorithms can be divided into 2 groups: Verb and Place. Verb effects allow user friendly control over medium to large spaces. Their decay times are controlled by Rvrb Time or LateRvbTim parameters, and Room Types range from rooms to large areas. Place algorithms on the other hand are optimized for small spaces. Decay time is controlled by the Absorption parameter, and Room Types offers several booths.
Each of these reverb algorithms combines several components: a diffuser, an injector, predelay, an ambience generator with feedback, and various filters. These components provide sonic building blocks for both the early reflection portions and the body of the reverb.
The ambience generator is the heart of each reverb algorithm and creates most of the ÔlateÕ reverb in algorithms with an Early Reflections circuit. It is comprised of a complex arrangement of delay lines to disperse the sound. By using feedback in conjunction with the ambience generator, a reverb tail is produced. The length of this reverb tail is controlled by the Rvrb Time parameter in the ÒVerbÓ algorithms, or the Absorption parameter in ÒPlaceÓ algorithms.
In order to create reverbs that are smoother and richer, some of the delays in the ambience generator are moved by LFOs. The LFOs are adjusted by using the LFO Rate and LFO Depth controls. When used subtly, unwanted artifacts such as flutter and ringing that are inherent in digital reverbs can be reduced.
In the feedback loop of the ambience generator are filters that further enhance the sonic properties of each reverb. A lowpass filter is controlled by HF Damping. Its action mimics high-frequency energy being absorbed as the sound travels around a room. A low shelving filter is controlled by LF Split and LF Time, which are used to shorten or lengthen the decay time of low frequency energy.
At the beginning of each algorithm are diffusers. A diffuser creates an initial ÒsmearingÓ quality on input signals usually before the signal enters the ambience generating loop. The DiffAmtScl and DiffLenScl parameters respectively change the amount and the length of time that the sound is smeared. The Diffuse reverbs, however, implement diffusion a little differently. See the section on Diffuse Verb and Diffuse Place below for detailed information.
Algorithm Reference-8
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
Some algorithms use injector mechanisms when feeding a signal into the ambience generator. An injector creates copies of the input signal at different delay intervals and feeds each copy into the ambience generator at different points. This results in finer control over the onset of the reverb. By tapering the amplitudes of early copies vs. late copies, the initial build of the reverb can be controlled. Inj Build controls this taper. Negative values create a slower build, while positive values create a faster build. Inj Spread scales the length of all the copies as a group. Inj Skew (Omni reverbs) delays one channel relative to the other before injecting into the ambience generator. Negative values delay the left side while positive values delay the right side. Inj LP controls the cutoff frequency of a 1 pole (6dB/oct) lowpass filter associated with the injector.
Predelay can give the illusion that a space is more voluminous. Separate control over left and right predelay is provided which can be used to de-correlate the center image, increasing reverb envelopment.
In addition to filters inside the ambience feedback loop, there also may be filters placed at the output of the reverb including a low shelf, high shelf, and/or lowpass.
Algorithms that utilize Early Reflection circuits use a combination of delays, diffusers, and filters to create ambience that is sparser than the late portion of the reverb. These early reflections model the initial near-discrete echoes rebounding directly off of near field surfaces before the reverb has a chance to become diffuse. They add realism when emulating real rooms and halls.
The starting point when creating a new reverb preset should be the Room Type parameter. This parameter selects the basic type of reverb. Due to the inherent complexity of reverb algorithms and the sheer number of variables responsible for their character, the Room Type parameter provides condensed preset collections of these variables. Each Room Type collection has been painstakingly selected by Kurzweil engineers to provide the best-sounding combination of mutually complementary variables modeling an assortment of reverb families. When a room type is selected, an entire incorporated set of delay lengths and diffusion settings are established within the algorithm. By using the Size Scale, DiffAmtScl, DiffLenScl, and Inj Spread parameters, you may scale individual elements away from their pre-defined values. When set to 1.00x, each of these elements are accurately representing their preset values determined by the current Room Type.
Room Types with similar names in different reverb algorithms do not sound the same. For example, Hall1 in Diffuse Verb does not sound the same as Hall1 in TQ Verb.
The Size Scale parameter scales the inherent size of the reverb chosen by Room Type. For a true representation of the selected Room Type size, set this to 1.00x. Scaling the size below this will create smaller spaces, while larger scale factors will create large spaces.
The InfinDecay switch is designed to override the Rvrb Time parameter and create a reverb tail with an infinite decay time when ÔOnÕ. However, certain HF Damping settings may reduce this effect, and cause the tail to taper away. This parameter is an excellent candidate for a KDFX Modulation, using a switch pedal as a source.
Algorithm Reference-9
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
Classic Verb and Classic Place:
Classic reverbs are 2-PAU algorithms with early reflections. The late portion consists of an input diffuser; ambience generator with low shelving filters, lowpass filters, and LFO moving delays; and predelay.
The early reflection portion consists of one delay per channel sent to its own output channel controlled by E Dly L and E Dly R, and one delay per channel sent to its opposite output channel controlled be E Dly LX and E Dly RX. Each of these delays also use a Diffuser. Diffusion lengths are separately controlled by E DifDly L, E DifDly R, E DifDly LX, and E DifDly RX while diffusion amounts are all adjusted with E DiffAmt.
The late reverb and early reflection portions are independently mixed together with the Late Lvl and EarRef Lvl controls. The wet signal is passed through a final high-shelving filter before being mixed with the dry signal.
L Input
R Input
DiffAmtScl DiffLenScl
Diffusor
DiffAmtScl DiffLenScl
Diffusor
LF Mult
HF Damping
HF Damping
LF Mult
Rvrb Time Absorption
Ambience
Rvrb Time Absorption
L ER Output
L Pre Dly
R Pre Dly
R ER Output
Late
Lvl
Late
Lvl
Signal flow of Classic Verb and Classic Place
E DfDlyScl E DiffAmt
(Apply to all Diffusors)
E DifDlyL
E Dly L
Diffusor
EarRef Lvl
EarRef Lvl
Treble
Treble
Blend
Dry
Wet
L Output
Out Gain
R Output
Wet
Dry
L ER Output
L Input
E Dly LX
E Dly RX
R Input
Early reflection portion of Classic Verb and Classic Place
Algorithm Reference-10
E Dly R
E DifDlyLX
Diffusor
E DifDlyR
Diffusor
E DifDlyRX
Diffusor
E Blend X
E Blend X
Blend
R ER Output
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
PAGE 1 (Classic Verb)
Wet/Dry -100 to 100% Out Gain Off; -79.0 to 24.0 dB
Rvrb Time 0.00 to 60.00 s EarRef Lvl -100 to 100%
HF Damping 0 to 25088 Hz Late Lvl -100 to 100%
L Pre Dly 0.0 to 230.0 ms R Pre Dly 0.0 to 230.0 ms
PAGE 1 (Classic Place)
Wet/Dry -100 to 100% Out Gain Off; -79.0 to 24.0 dB
Absorption 0 to 100% EarRef Lvl -100 to 100%
HF Damping 0 to 25088 Hz Late Lvl -100 to 100%
L Pre Dly 0.0 to 230.0 ms R Pre Dly 0.0 to 230.0 ms
PAGE 2 (Classic Verb)
Room Type Hall1, ... DiffAmtScl 0.00 to 2.00 x
Size Scale 0.01 to 2.00x DiffLenScl 0.00 to 2.00 x
InfinDecay On or Off LFO Rate 0.01 to 10.00 Hz
LFO Depth 0.0 to 100.0 ct
TrebShlf F 16 to 25088 Hz LF Split 16 to 25088 Hz
TrebShlf G -79.0 to 24.0 dB LF Time 0.50 to 1.50 x
PAGE 2 (Classic Place)
Room Type Booth1, ... DiffAmtScl 0.00 to 2.00 x
Size Scale 0.01 to 2.00x DiffLenScl 0.00 to 2.00 x
LFO Rate 0.01 to 10.00 Hz
LFO Depth 0.0 to 100.0 ct
TrebShlf F 16 to 25088 Hz LF Split 16 to 25088 Hz
TrebShlf G -79.0 to 24.0 dB LF Time 0.50 to 1.50 x
PAGE 3
E DfDlyScl 0.00 to 2.00 x E X Blend 0 to 100%
E DiffAmt -100 to 100%
E Dly L 0.0 to 720.0 ms E Dly R 0.0 to 720.0 ms
E Dly LX 0.0 to 720.0 ms E Dly RX 0.0 to 720.0 ms
E DifDlyL 0.0 to 160.0 ms E DifDlyR 0.0 to 160.0 ms
E DifDlyLX 0.0 to 230.0 ms E DifDlyRX 0.0 to 230.0 ms
Algorithm Reference-11
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
TQ Verb and TQ Place:
TQ reverbs are 3-PAU algorithms with early reflections. The late portion consists of an input diffuser, injector, ambience generator with a lowpass filter, low shelving filter, and LFO moving delays, and predelay.
The early reflection portion combines a combination of delays, diffusers, and feedback. The relative delay lengths are all fixed but are scalable with the E Dly Scl parameter. Relative diffusion lengths are also fixed, and are scalable with the E DfLenScl parameter. Diffusion amounts are adjusted with E DiffAmt. The E Build parameter ramps the gains associated with each delay line in a way that changes the characteristic of the onset of the early reflections. Negative amounts create a slower onset while positive amounts create a faster onset.
The late reverb and early reflection portions are independently mixed together with the Late Lvl and EarRef Lvl controls. The wet signal is passed through a final high shelving filter before being mixed with the dry signal.
L Input
DiffAmtScl DiffLenScl
DiffAmtScl DiffLenScl
R Input
Diffuser
Diffuser
L Pre Dly
R Pre Dly
Inj LP
Inj LP
InjBuild InjSpread
Injector
Injector
InjBuild InjSpread
Reverb Time
LF Mult
Ambience
LF Mult
Reverb Time
Absorption
Absorption
L ER Output
HF Damping
HF Damping
R ER Output
EarRef Lvl
Late Lvl
Late Lvl
EarRef Lvl
Signal flow of TQ Verb and TQ Place
Treble
Treble
Wet
Wet
Dry
Out
Gain
Out
Gain
Dry
L Output
R Output
Algorithm Reference-12
E Dly Scl (Applies to All Delays)
Delay
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
Diffusor
L Input
E PreDly L
E Fdbk Amt
Delay
Delay
Diffusor
Diffusor
E Build
Delay
Delay
E Build
Diffusor
Diffusor
Diffusor
R Input
E PreDly R
Delay
Delay
Delay
Early reflection portion of TQ Verb and TQ Place
PAGE 1 (TQ Verb)
Wet/Dry -100 to 100% Out Gain Off; -79.0 to 24.0 dB
Rvrb Time 0.00 to 60.00 s EarRef Lvl -100 to 100%
HF Damping 0 to 25088 Hz Late Lvl -100 to 100%
L Pre Dly 0.0 to 230.0 ms R Pre Dly 0.0 to 230.0 ms
L ER Output
R ER Output
PAGE 1 (TQ Place)
Wet/Dry -100 to 100% Out Gain Off; -79.0 to 24.0 dB
Absorption 0 to 100% EarRef Lvl -100 to 100%
HF Damping 0 to 25088 Hz Late Lvl -100 to 100%
L Pre Dly 0.0 to 230.0 ms R Pre Dly 0.0 to 230.0 ms
PAGE 2 (TQ Verb)
Room Type Hall1, ... TrebShlf F 16 to 25088 Hz
Size Scale 0.00 to 2.50x TrebShlf G -79.0 to 24.0 dB
InfinDecay On or Off DiffAmtScl 0.00 to 2.00 x
DiffLenScl 0.00 to 2.50 x
LF Split 16 to 25088 Hz LFO Rate 0.01 to 10.00 Hz
LF Time 0.50 to 1.50 x LFO Depth 0.0 to 100.0 ct
Algorithm Reference-13
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
PAGE 2 (TQ Place)
Room Type Booth1, ... TrebShlf F 16 to 25088 Hz
Size Scale 0.00 to 2.50x TrebShlf G -79.0 to 24.0 dB
DiffAmtScl 0.00 to 2.00 x
DiffLenScl 0.00 to 2.50 x
LF Split 16 to 25088 Hz LFO Rate 0.01 to 10.00 Hz
LF Time 0.50 to 1.50 x LFO Depth 0.0 to 100.0 ct
PAGE 3
Inj Build -100 to 100% Inj LP 16 to 25088 Hz
Inj Spread 0.00 to 2.50 x
E DiffAmt -100 to 100% E Build -100 to 100%
E DfLenScl 0.00 to 2.50 x E Fdbk Amt -100 to 100%
E DlyScl 0.00 to 2.50 x E HF Damp 16 to 25088 Hz
E PreDlyL 0.0 to 150.0 ms E PreDlyR 0.0 to 150.0 ms
Algorithm Reference-14
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
Diffuse Verb and Diffuse Place:
Diffuse reverbs are 3-PAU algorithms and are characterized as such because of the initial burst of diffusion inherent in the onset of the reverb. Each of these algorithms consists of an input diffuser; ambience generator with a lowpass filter, low shelving filter, and LFO moving delays; and predelay.
In the Diffuse reverbs, the diffuser is implemented a little differently. The diffuser is just inside the ambience generation loop, so changes in diffusion create changes in the reverb decay. The Diffuse reverbs also offer DiffExtent and Diff Cross parameters. DiffExtent selects one of seven arbitrary gate-time lengths of the initial diffusion burst, while Diff Cross adjusts the combination of left and right channels that are diffused.
L Input
R Input
LF Mult
DiffExtent
Diff Cross
Diffusor Ambience
DiffAmtScl
DiffLenScl
LF Mult
LateRvbTim Absorption
LateRvbTim Absorption
HF Damping
HF Damping
L Pre Dly
R Pre Dly
Signal flow of Diffuse Verb and Diffuse Place
Lopass
Lopass
Dry
Wet
L Output
Out Gain
R Output
Wet
Dry
Algorithm Reference-15
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
PAGE 1 (Diffuse Verb)
Wet/Dry -100 to 100% Out Gain Off; -79.0 to 24.0 dB
LateRvbTim 0.00 to 60.00 s
HF Damping 0 to 25088 Hz Lopass 16 to 25088 Hz
L Pre Dly 0.0 to 230.0 ms R Pre Dly 0.0 to 230.0 ms
PAGE 1 (Diffuse Place)
Wet/Dry -100 to 100% Out Gain Off; -79.0 to 24.0 dB
Absorption 0 to 100%
HF Damping 0 to 25088 Hz Lopass 16 to 25088 Hz
L Pre Dly 0.0 to 230.0 ms R Pre Dly 0.0 to 230.0 ms
PAGE 2 (Diffuse Verb)
Room Type Hall1,... DiffExtent 1 to 7 x
Size Scale 0.01 to 2.50x Diff Cross -100 to 100%
InfinDecay On or Off DiffAmtScl 0.00 to 2.00 x
DiffLenScl 0.01 to 2.50 x
LF Split 16 to 25088 Hz LFO Rate 0.01 to 10.00 Hz
LF Time 0.50 to 1.50 x LFO Depth 0.0 to 100.0 ct
PAGE 2 (Diffuse Place)
Room Type Booth1, ... DiffExtent 1 to 7 x
Size Scale 0.01 to 2.50x Diff Cross -100 to 100%
DiffAmtScl 0.00 to 2.00 x
DiffLenScl 0.01 to 2.50 x
LF Split 16 to 25088 Hz LFO Rate 0.01 to 10.00 Hz
LF Time 0.50 to 1.50 x LFO Depth 0.0 to 100.0 ct
Algorithm Reference-16
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
OmniVerb and OmniPlace:
Omni reverbs are 3-PAU algorithms that consist of an input diffuser; injector; ambience generator with a lowpass filter, low shelving filter, and LFO moving delays; and predelay.
The Expanse parameter adjusts the amount of reverb energy that is fed to the edges of the stereo image. A value of 0% will concentrate energy in the center of the image, while non-zero values will spread it out. Positive and negative values will impose different characteristics on the reverb image.
At the output of the reverb are a pair each of low-shelving and high-shelving filters.
L Input
Reverb Time
LF Mult
Absorption
HF Damping
L Pre Dly
Treble
Bass
Wet
Dry
Out
Gain
L Output
DiffAmtScl DiffLenScl
Diffuser
Lopass
Inj Build Inj Spread Inj Skew
Injector
Ambience
DiffAmtScl DiffLenScl
R Input
Diffuser
Lopass
Injector R Pre Dly
Inj Build Inj Spread Inj Skew
LF Mult
Reverb Time
Absorption
HF Damping
Treble
Bass
Signal flow of OmniVerb and OmniPlace
PAGE 1 (OmniVerb)
Wet/Dry -100 to 100% Out Gain Off; -79.0 to 24.0 dB
Rvrb Time 0.00 to 60.00 s
HF Damping 0 to 25088 Hz Lopass 16 to 25088 Hz
L Pre Dly 0.0 to 230.0 ms R Pre Dly 0.0 to 230.0 ms
PAGE 1 (OmniPlace)
Wet/Dry -100 to 100% Out Gain Off; -79.0 to 24.0 dB
Absorption 0 to 100%
HF Damping 0 to 25088 Hz Lopass 16 to 25088 Hz
L Pre Dly 0.0 to 230.0 ms R Pre Dly 0.0 to 230.0 ms
Wet
Out
Gain
R Output
Dry
Algorithm Reference-17
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
PAGE 2 (OmniVerb)
Room Type Hall1, ... Expanse -100 to 100%
Size Scale 0.00 to 2.50x
InfinDecay On or Off DiffAmtScl 0.00 to 2.00 x
DiffLenScl 0.00 to 4.50 x
LF Split 16 to 25088 Hz LFO Rate 0.01 to 10.00 Hz
LF Time 0.50 to 1.50 x LFO Depth 0.0 to 100.0 ct
PAGE 2 (OmniPlace)
Room Type Booth1, ... Expanse -100 to 100%
Size Scale 0.00 to 2.50x
DiffAmtScl 0.00 to 2.00 x
DiffLenScl 0.00 to 4.50 x
LF Split 16 to 25088 Hz LFO Rate 0.01 to 10.00 Hz
LF Time 0.50 to 1.50 x LFO Depth 0.0 to 100.0 ct
PAGE 3
TrebShlf F 16 to 25088 Hz
Inj Build -100 to 100% TrebShlf G -79.0 to 24.0 dB
Inj Spread 0.00 to 4.50 x BassShlf F 16 to 25088 Hz
Inj Skew -200 to 200 ms BassShlf G -79.0 to 24.0 dB
Absorption
This controls the amount of reßective material that is in the space being emulated, much like an acoustical absorption coefÞcient. The lower the setting, the longer it will take for the sound to die away. A setting of 0% will cause an inÞnite decay time.
Rvrb Time Adjusts the basic decay time of the late portion of the reverb.
LateRvbTim Adjusts the basic decay time of the late portion of the reverb after diffusion.
HF Damping This controls the amount of high frequency energy that is absorbed as the reverb decays.
The values set the cutoff frequency of the 1-pole (6dB/oct) lowpass Þlter within the reverb feedback loop.
L Pre Dly, R Pre Dly These control the amount that each channel of the reverb is delayed relative to the dry
signal. Setting different lengths for both channels can de-correlate the center portion of the reverb image and make it seem wider. This only affects the late reverb in algorithms that have early reßections.
Lopass Controls the cutoff frequency of a 1-pole (6dB/oct) lowpass Þlter at the output of the
reverb. This only affects the late reverb in algorithms that have early reßections.
EarRef Lvl Adjusts the mix level of the early reßection portion of algorithms offering early
reßections.
Late Lvl Adjusts the mix level of the late reverb portion of algorithms offering early reßections.
Algorithm Reference-18
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
Room Type This parameter selects the basic type of reverb being emulated, and should be the
starting point when creating your own reverb presets. Due to the inherent complexity of reverb algorithms and the sheer number of variables responsible for their character, the Room Type parameter provides condensed preset collections of these variables. Each Room Type preset has been painstakingly selected by Kurzweil engineers to provide the best sounding collection of mutually complementary variables modeling an assortment of reverb families. When a room type is selected, an entire incorporated set of delay lengths and diffusion settings are established within the algorithm. By using the Size Scale, DiffAmtScl, DiffLenScl, and Inj Spread parameters, you may scale individual elements away from their preset value. When set to 1.00x, each of these elements is accurately representing its preset value determined by the current Room Type.
Room Types with similar names in different reverb algorithms do not sound the same. For example, Hall1 in Diffuse Verb does not sound the same as Hall1 in TQ Verb.
Size Scale This parameter scales the inherent size of the reverb chosen by Room Type. For a true
representation of the selected Room Type size, set this to 1.00x. Scaling the size below this will create smaller spaces, while larger scale factors will create large spaces.
InÞnDecay Found in ÒVerbÓ algorithms. When turned ÒOnÓ, the reverb tail will decay indeÞnitely.
However, certain HF Damping settings may reduce this effect, and cause the tail to taper away. When turned ÒOffÓ, the decay time is determined by the ÒRvrb TimeÓ or ÒLateRvbTimÓ parameters. This parameter is an excellent candidate for a KDFX Modulation, using a switch pedal as a source.
LF Split Used in conjunction with LF Time. This controls the upper-frequency limit of the low-
frequency decay time multiplier. Energy below this frequency will decay faster or slower depending on the LF Time parameter.
LF Time Used in conjunction with LF Split. This modiÞes the decay time of the energy below the
LF Split frequency. A setting of 1.00x will make low-frequency energy decay at the rate determined by the decay time. Higher values will cause low-frequency energy to decay slower, and lower values will cause it to decay more quickly.
TrebShlf F Adjusts the frequency of a high-shelving Þlter at the output of the late reverb.
TrebShlf G Adjusts the gain of a high-shelving Þlter at the output of the late reverb.
BassShlf F Adjusts the frequency of a low-shelving Þlter at the output of the late reverb.
BassShlf G Adjusts the gain of a low-shelving Þlter at the output of the late reverb.
DiffAmtScl Adjusts the amount of diffusion at the onset of the reverb. For a true representation of
the selected Room Type diffusion amount, set this to 1.00x.
DiffLenScl Adjusts the length of the diffusion at the onset of the reverb. For a true representation of
the selected Room Type diffusion length, set this to 1.00x.
DiffExtent Adjust the onset diffusion duration. Higher values create longer diffuse bursts at the
onset of the reverb.
Diff Cross Adjusts the onset diffusion cross-coupling character. Although subtle, this parameter
bleeds left and right channels into each other during onset diffusion, and also in the body of the reverb. 0% setting will disable this. Increasing this value in either the positive or negative direction will increase its effect.
Expanse Amount of late reverb energy biased toward the edges of the stereo image. A setting of
0% will bias energy towards the center. Moving away from 0% will bias energy towards the sides. Positive and negative values will have a different character.
Algorithm Reference-19
FXAlgs #4-11: Classic ¥ TQ ¥ Diffuse ¥ Omni reverbs
LFO Depth Adjusts the detuning depth in cents caused by a moving reverb delay line. Moving delay
lines can imitate voluminous ßowing air currents and reduce unwanted artifacts like ringing and ßutter when used properly. Depth settings under 1.5ct with LFO Rate settings under 1.00Hz are recommended for modeling real spaces. High depth settings can create chorusing qualities, which wonÕt be suitable for real acoustic spaces, but can nonetheless create interesting effects. Instruments that have little or no inherent pitch ßuctuation (like piano) are much more sensitive to this LFO than instruments that normally have a lot of vibrato (like voice) or non-pitched instruments (like snare drum).
LFO Rate Adjusts the rate at which the moving reverb delay lines move.
Inj Build Used in conjunction with Inj Spread, this adjusts the envelope of the onset of the reverb.
SpeciÞcally, it tapers the amplitudes of a series of delayed signals injected into the body of the reverb. Values above 0% will produce a faster build, while values below 0% will cause the build to be more gradual.
ead Used in conjunction with Inj Build, this scales the length of the series of delays injected
Inj Spr
into the body of the reverb. For a true representation of the selected Room Type injector spread, set this to 1.00x.
Inj LP This adjusts the cutoff frequency of a 1 pole (6dB/oct) lowpass Þlter applied to the signal
being injected into the body of the reverb.
Inj Skew Adjusts the amount of delay applied to either the left or right channel of the reverb
injector. Positive values delay the right channel while negative values delay the left channel.
E DiffAmt Adjusts the amount of diffusion applied to the early reßection network.
E DfLenScl Adjusts the length of diffusion applied to the early reßection network. This is inßuenced
by E PreDlyL and E PreDlyR.
E Dly Scl Scales the delay lengths inherent in the early reßection network.
E Build Adjusts the envelope of the onset of the early reßections. Values above 0% will create a
faster attack while values below 0% will create a slower attack.
E Fdbk Amt Adjusts the amount of the output of an early reßection portion that is fed back into the
input of the opposite channel in front of the early pre-delays. Overall, it lengthens the decay rate of the early reßection network. Negative values polarity-invert the feedback signal.
E HF Damp This adjusts the cutoff frequency of a 1-pole (6dB/oct) lowpass Þlter applied to the early
reßection feedback signal.
E PreDlyL, E PreDlyR Adjusts how much the early reßections are delayed relative to the dry signal. These are
independent of the late reverb predelay times, but will inßuence E Dly Scl.
E Dly L, E Dly R Adjusts the left and right early reßection delays fed to the same output channels.
E Dly LX, E Dly RX Adjusts the left and right early reßection delays fed to the opposite output channels.
E DifDlyL, E DifDlyR Adjusts the diffusion delays of the diffusers on delay taps fed to the same output
channels.
E DifDlyLX, E DifDlyRX Adjusts the diffusion delays of the diffusers on delay taps fed to the opposite output
channels.
E X Blend Adjusts the balance between early reßection delay tap signals with diffusers fed to their
same output channel, and those fed to opposite channels. 0% allows only delay taps being fed to opposite output channels to be heard, while 100% allows only delay taps going to the same channels to be heard.
Algorithm Reference-20
FXAlg #12: Panaural Room
FXAlg #12: Panaural Room
Room reverberation algorithm
Allocation Units: 3
The Panaural Room reverberation is implemented using a special network arrangement of many delay lines that guarantees colorless sound. The reverberator is inherently stereo with each input injected into the ÒroomÓ at multiple locations. The signals entering the reverberator first pass through a shelving bass equalizer with a range of +/-15dB. To shorten the decay time of high frequencies relative to mid frequencies, lowpass filters controlled by HF Damping are distributed throughout the network. Room Size scales all the delay times of the network (but not the Pre Dly or Build Time), to change the simulated room dimension over a range of 1 to 16m. Decay Time varies the feedback gains to achieve decay times from 0.5 to 100 seconds. The Room Size and Decay Time controls are interlocked so that a chosen Decay Time will be maintained while Room Size is varied. A two-input stereo mixer, controlled by Wet/Dry and Out Gain, feeds the output.
Dry
L Input
R Input
PreDelay
PreDelay
Dry
Reverb
Wet
Out Gain
L Output
R Output
Simplified block diagram of Panaural Room.
The duration and spacing of the early reflections are influenced by Room Size and Build Time, while the number and relative loudness of the individual reflections are influenced by Build Env. When Build Env is near 0 or 100%, fewer reflections are created. The maximum number of important early reflections, 13, is achieved at a setting of 50%.
To get control over the growth of reverberation, the left and right inputs each are passed through an ÒinjectorÓ that can extend the source before it drives the reverberator. Only when Build Env is set to 0% is the reverberator driven in pure stereo by the pure dry signal. For settings of Build Env greater than 0%, the reverberator is fed multiple times. Build Env controls the injector so that the reverberation begins abruptly (0%), builds immediately to a sustained level (50%), or builds gradually to a maximum (100%). Build Time varies the injection length over a range of 0 to 500ms. At a Build Time of 0ms, there is no extension of the build time. In this case, the Build Env control adjusts the density of the reverberation, with maximum density at a setting of 50%. In addition to the two build controls, there is an overall Pre Dly control that can delay the entire reverberation process by up to 500ms.
Algorithm Reference-21
FXAlg #12: Panaural Room
Parameters:
PAGE 1
Wet/Dry 0 to 100%wet Out Gain Off, -79.0 to 24.0
Room Size 1.0 to 16.0 m
Pre Dly 0 to 500 ms Decay Time 0.5 to 100.0 s
HF Damping 16 to 25088 Hz
PAGE 2
Bass Gain -15 to 15 dB Build Time 0 to 500 ms
Build Env 0 to 100%
Wet/Dry The amount of the stereo reverberator (wet) signal relative to the original input (dry)
signal to be output. The dry signal is not affected by the Bass Gain control. The wet signal is affected by the Bass Gain control and by all the other reverberator controls. The balance between wet and dry signals is an extremely important factor in achieving a good mix. Emphasizing the wet signal gives the effect of more reverberation and of greater distance from the source.
Out Gain
Decay Time The reverberation decay time (mid-band ÒRT60Ó), the time required before the
HF Damping Adjusts lowpass Þlters in the reverberator so that high frequencies die away more
Bass Gain Shapes the overall reverberation signalÕs bass content, but does not modify the decay
Room Size Choosing an appropriate room size is very important in getting a good reverberation
Pre Dly Introducing predelay creates a gap of silence that allows the dry signal to stand out with
Build Time Similar to predelay, but more complex, larger values of Build Time slow down the
The overall output level for the reverberation effect, and controls the level for both the wet and dry signal paths.
reverberation has died away to 60dB below its ÒrunningÓ level. Adjust decay time according to the tempo and articulation of the music and to taste.
quickly than mid and low frequencies. This shapes the reverberation for a more natural, more acoustically accurate sound.
time. Reduce the bass for a less muddy sound, raise it slightly for a more natural acoustic effect.
effect. For impulsive sources, such as percussion instruments or plucked strings, increase the size setting until discrete early reßections become audible, and then back it off slightly. For slower, softer music, use the largest size possible. At lower settings, Room Size leads to coloration, especially if the Decay Time is set too high.
greater clarity and intelligibility against the reverberant background. This is especially helpful with vocal or classical music.
building up of reverberation and can extend the build-up process. Experiment with Build Time and Build Env and use them to optimize the early details of reverberation. A Build Time of 0ms and a Build Env of 50% is a good default setting that yields a fast arriving, maximally dense reverberation.
Algorithm Reference-22
FXAlg #12: Panaural Room
Build Env When Build Time has been set to greater than about 80ms, Build Env begins to have an
audible inßuence on the early unfolding of the reverberation process. For lower-density reverberation that starts cleanly and impulsively, use a setting of 0%. For the highest­density reverberation, and for extension of the build-up period, use a setting of 50%. For an almost reverse reverberation, set Build Env to 100%. You can think of Build Env as setting the position of a see-saw. The left end of the see-saw represents the driving of the reverberation at the earliest time, the pivot point as driving the reverberation at mid­point in the time sequence, and the right end as the last signal to drive the reverberator. At settings near 0%, the see-saw is tilted down on the right: the reverberation starts abruptly and the drive drops with time. Near 50%, the see-saw is level and the reverberation is repeatedly fed during the entire build time. At settings near 100%, the see-saw is tilted down on the left, so that the reverberation is hit softly at Þrst, and then at increasing level until the end of the build time.
Algorithm Reference-23
FXAlg #13: Stereo Hall
FXAlg #13: Stereo Hall
A stereo hall reverberation algorithm
Allocation Units: 3
The Stereo Hall reverberation is implemented using a special arrangement of all pass networks and delay lines, which reduces coloration and increases density. The reverberator is inherently stereo with each input injected into the ÒroomÓ at multiple locations. To shorten the decay time of low and high frequencies relative to mid frequencies, bass equalizers and lowpass filters, controlled by Bass Gain and by HF Damping, are placed within the network. Room Size scales all the delay times of the network (but not the Pre Dly or Build Time), to change the simulated room dimension over a range of 10 to 75m. Decay Time varies the feedback gains to achieve decay times from 0.5 to 100 seconds. The Room Size and Decay Time controls are interlocked so that a chosen Decay Time will be maintained while Room Size is varied. At smaller sizes, the reverb becomes quite colored and is useful only for special effects. A two-input stereo mixer, controlled by Wet/Dry and Out Gain, feeds the output. The Lowpass control acts only on the wet signal and can be used to smooth out the reverb high end without modifying the reverb decay time at high frequencies.
Dry
L Input
R Input
PreDelay
PreDelay
Reverb
Dry
Wet
L Output
Out Gain
R Output
Simplified block diagram of Stereo Hall.
Within the reverberator, certain delays can be put into a time varying motion to break up patterns and to increase density in the reverb tail. Using the LFO Rate and Depth controls carefully with longer decay times can be beneficial. But beware of the pitch-shifting artifacts which can accompany randomization when it is used in greater amounts. Also within the reverberator, the Diffusion control can reduce the diffusion provided by some all pass-networks. While the reverb will eventually reach full diffusion regardless of the Diffusion setting, the early reverb diffusion can be reduced, which sometimes is useful to help keep the dry signal Òin the clearÓ.
The reverberator structure is stereo and requires that the dry source be applied to both left and right inputs. If the source is mono, it should still be applied (pan centered) to both left and right inputs. Failure to drive both inputs will result in offset initial reverb images and later ping-ponging of the reverberation. Driving only one input will also increase the time required to build up reverb density.
Algorithm Reference-24
FXAlg #13: Stereo Hall
To gain control over the growth of reverberation, the left and right inputs each are passed through an ÒinjectorÓ that can extend the source before it drives the reverberator. Only when Build Env is set to 0% is the reverberator driven in pure stereo by the pure dry signal. For settings of Build Env greater than 0%, the reverberator is fed multiple times. Build Env controls the injector so that the reverberation begins abruptly (0%), builds immediately to a sustained level (50%), or builds gradually to a maximum (100%). Build Time varies the injection length over a range of 0 to 500ms. At a Build Time of 0ms, there is no extension of the build time. In this case, the Build Env control adjusts the density of the reverberation, with maximum density at a setting of 50%. In addition to the two build controls, there is an overall Pre Dly control that can delay the entire reverberation process by up to 500ms.
Parameters:
PAGE 1
Wet/Dry 0 to 100%wet Out Gain Off, -79.0 to 24.0 dB
Room Size 2.0 to 15.0 m Diffusion 0 to 100%
Pre Dly 0 to 500 ms Decay Time 0.5 to 100.0 ms
HF Damping 16 to 25088 Hz
PAGE 2
Bass Gain -15 to 0 dB Build Time 0 to 500 ms
Lowpass 16 to 25088 Hz Build Env 0 to 100%
LFO Rate 0.00 to 5.10 Hz
LFO Depth 0.00 to 10.20 ct
W
et/Dry The amount of the stereo reverberator (wet) signal relative to the original input (dry)
signal to be output. The dry signal is not affected by the Bass Gain control. The wet signal is affected by the Bass Gain control and by all the other reverberator controls. The balance between wet and dry signals is an extremely important factor in achieving a good mix. Emphasizing the wet signal gives the effect of more reverberation and of greater distance from the source.
Out Gain The overall output level for the reverberation effect, and controls the level for both the
wet and dry signal paths.
Decay Time The reverberation decay time (mid-band ÒRT60Ó), the time required before the
reverberation has died away to 60dB below its ÒrunningÓ level. Adjust decay time according to the tempo and articulation of the music and to taste.
HF Damping Adjusts lowpass Þlters in the reverberator so that high frequencies die away more
quickly than mid and low frequencies. This shapes the reverberation for a more natural, more acoustically accurate sound.
Room Size Choosing an appropriate room size is very important in getting a good reverberation
effect. For impulsive sources, such as percussion instruments or plucked strings, increase the size setting until discrete early reßections become audible, and then back it off slightly. For slower, softer music, use the largest size possible. At lower settings, RoomSize leads to coloration, especially if the DecayTime is set too high.
Bass Gain Adjusts bass equalizers in the reverberator so that low frequencies die away more
quickly than mid and high frequencies. This can be used to make the reverberation less muddy.
Algorithm Reference-25
FXAlg #13: Stereo Hall
Lowpass Used to shape the overall reverberation signal's treble content, but does not modify the
decay time. Reduce the treble for a softer, more acoustic sound.
Pre Dly Introducing predelay creates a gap of silence that allows the dry signal to stand out with
greater clarity and intelligibility against the reverberant background. This is especially helpful with vocal or classical music.
Build Time Similar to predelay, but more complex, larger values of BuildTime slow down the
building up of reverberation and can extend the build up process. Experiment with BuildTime and BuildEnv and use them to optimize the early details of reverberation. A BuildTime of 0ms and a BuildEnv of 50% is a good default setting that yields fast arriving, natural reverberation.
Build Env When BuildTime has been set to greater than about 80ms, BuildEnv begins to have an
audible inßuence on the early unfolding of the reverberation process. For lower-density reverberation that starts cleanly and impulsively, use a setting of 0%. For the highest­density reverberation, and for extension of the build-up period, use a setting of 50%. For an almost reverse reverberation, set BuildEnv to 100%. You can think of BuildEnv as setting the position of a see-saw. The left end of the see-saw represents the driving of the reverberation at the earliest time, the pivot point as driving the reverberation at mid­point in the time sequence, and the right end as the last signal to drive the reverberator. At settings near 0%, the see-saw is tilted down on the right: the reverberation starts abruptly and the drive drops with time. Near 50%, the see-saw is level and the reverberation is repeatedly fed during the entire build time. At settings near 100%, the see-saw is tilted down on the left, so that the reverberation is hit softly at Þrst, and then at increasing level until the end of the build time.
LFO Rate
and LFO Depth Within the reverberator, the certain delay values can be put into a time varying
motion to break up patterns and to increase density in the reverb tail. Using the LFO Rate and Depth controls carefully with longer decay times can be beneÞcial. But beware of the pitch-shifting artifacts which can accompany randomization when it is used in greater amounts.
Diffusion Within the reverberator, the Diffusion control can reduce the diffusion provided by some
of the all-pass networks. While the reverb will eventually reach full diffusion regardless of the Diffusion setting, the early reverb diffusion can be reduced, which sometimes is useful to help keep the dry signal "in the clear."
Algorithm Reference-26
FXAlg #14: Grand Plate
FXAlg #14: Grand Plate
A plate reverberation algorithm
Allocation Units: 3
This algorithm emulates an EMT 140 steel plate reverberator. Plate reverberators were manufactured during the 1950s, 60s, 70s, and perhaps into the 80s. By the end of the 1980s, they had been supplanted in the marketplace by digital reverberators, which first appeared in 1976. While a handful of companies made plate reverberators, EMT (Germany) was the best known and most popular.
Dry
L Input
R Input
Diagram of Grand Plate reverb
A plate reverberator is generally quite heavy and large, perhaps 4 feet high by 7 feet long, and a foot thick. They were only slightly adjustable, with controls for high frequency damping and decay time. Some were stereo in/stereo out, others mono in/mono out.
A plate reverb begins with a sheet of plate steel suspended by its edges, leaving the plate free to vibrate. At one (or two) points on the plate, an electromagnetic driver (sort of a small loudspeaker without a cone) is arranged to couple the dry signal into the plate, sending sound vibrations into the plate in all directions. At one or two other locations, a pickup is placed, sort of like a dynamic microphone whose diaphragm is the plate itself, to pick up the reverberation.
Since the sound waves travel very rapidly in steel (faster than they do in air), and since the dimensions of the plate are not large, the sound quickly reaches the plate edges and reflects from them. This results in a very rapid build­up of the reverberation, essentially free of early reflections and with no distinguishable gap before the onset of reverb.
PreDelay
PreDelay
Dry
Plate
Reverb
Wet
Out Gain
Plates offered a wonderful sound of their own, easily distinguished from other reverberators in the pre-digital reverb era, such as springs or actual ÒechoÓ chambers. Plates were bright and diffused (built up echo density) rapidly. Curiously, when we listen to a vintage plate today, we find that the much vaunted brightness is nothing like what we can accomplish digitally; we actually have to deliberately reduce the brightness of a plate emulation to match the sound of a real plate. Similarly, we find that we must throttle back on the low frequency content as well.
Algorithm Reference-27
FXAlg #14: Grand Plate
The algorithm developed for Grand Plate was carefully crafted for rapid diffusion, low coloration, freedom from discrete early reflections, and ÒbrightnessÓ. We also added some controls that were never present in real plates: size, predelay of up to 500ms, LF damping, lowpass roll off, and bass roll off. Furthermore, we allow a wider range of decay time adjustment than a conventional plate. Once the algorithm was complete, we tuned it by listening to the original EMT reverb on one channel and the Grand Plate emulation on the other. A lengthy and careful tuning of Grand Plate (tuning at the micro detail level of each delay and gain in the algorithm) was carried out until the stereo spread of this reverb was matched in all the time periodsÑearly, middle, and late.
The heart of this reverb is the plate simulation network, with its two inputs and two outputs. It is a full stereo reverberation network, which means that the left and right inputs get slightly different treatment in the reverberator. This yields a richer, more natural stereo image from stereo sources. If you have a mono source, assign it to both inputs for best results.
The incoming left source is passed through predelay, lowpass (Lowpass), and bass-shelf (Bass Gain) blocks. The right source is treated similarly.
There are lowpass filters (HF Damping) and high pass filters (LF Damping) embedded in the plate simulation network to modify the decay times. The reverb network also accommodates the Room Size and Decay Time controls.
An output mixer assembles dry and wet signals.
Parameters:
PAGE 1
Wet/Dry 0 to 100%wet Out Gain Off, -79.0 to 24.0 dB
Room Size 1.00 to 4.00 m
Pre Dly 0 to 500 ms Decay Time 0.2 to 5.0 s
HF Damping 16 to 25088 Hz LF Damping 1 to 294 Hz
PAGE 2
Lowpass 16 to 25088 Hz Bass Gain -15 to 0 dB
Wet/Dry The amount of the stereo reverberator (wet) signal relative to the original input (dry)
signal sent to the output. The dry signal is not affected by the Lowpass or Bass Gain controls. The wet signal is affected by the Lowpass and Bass Gain controls and by all the other reverberator controls. The balance between wet and dry signals is an extremely important factor in achieving a good mix. Emphasizing the wet signal gives the effect of more reverberation and of greater distance from the source.
Out Gain The overall output level for the reverberation effect and controls the level for both the
wet and dry signal paths.
Room Size Choosing an appropriate room size is very important in getting a good reverberation
effect. For impulsive sources, such as percussion instruments or plucked strings, increase the size setting until discrete reßections become audible, and then back it off slightly. For slower, softer music, use the largest size possible. At lower settings, Room Size leads to coloration, especially if the Decay Time is set too high. To emulate a plate reverb, this control is typically set to 1.9m.
Pre Dly Introducing predelay creates a gap of silence that allows the dry signal to stand out with
greater clarity and intelligibility against the reverberant background. This is especially helpful with vocals or classical music.
Algorithm Reference-28
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