puzzlefactory Limiter6 User Manual

Preface

I'm glad to introduce public alpha version of new limiter plugin (codename "Limiter6")!

This plugin is unique combination of slow RMS-compressor, peak limiter, high-frequency
limiter, oversampled clipper and inter-sample limiter. The idea of this combination is "gain
staging" when each stage used a little to make a most clean sound.

This is not a plugin with 1 knob and smart brain inside, which allow making your mix 0 dB
RMS. All settings are manual and there're a lot of knobs.

The GUI is a draft yet and will be redrawn to photorealistic military style.

Modules and parameters description

In the beginning of the work you should set "Stereo" / "Mono" mode. When plugin is using on
mono track you should set it to "Mono".

To the right from "Stereo" / "Mono" mode there's invisible "Realtime" parameter switch. By
default the plugin uses maximum latency (about 28 ms) to allow "smooth" turning on/off
modules and changing parameters, which cause processing latency to change. If minimum
latency is required the plugin can be switched in "Realtime" mode by clicking on this empty
space. "Realtime" label will appear.

=== 1. "RMS compressor" ===

This module is a very slow RMS compressor. It's used to stabilize crest-factor of signal before
peak-limiting modules. Also this module was created under impression of slow release curves of
RS124 compressor.

Typical usage examples:

1. Achieving manual "gain riding" effect when the sound in loud passages becomes quieter
and in quieter passages becomes louder.

2. Softening the attacks (if "lookahead" mode is on").

3. When signal reaches the level where peak-limiting modules start to distort the sound
level automatically lowers.

Parameters:

"Compressor" – turns on ("On") or turns off ("Bypass") the compressor.

"Gain" – controls signal level at the compressor input.

"Threshold" – controls the compressor threshold.

"Ratio" – controls dynamic range compression ratio (you should lower the value to achieve
"invisible" compression effect).

"Lookahead" – if the parameter set to "On" and the attack time is set to minimum the compressor
starts to suppress attacks of the signal. If the parameter set to "Off" the compressor passes signal
attacks through.

"Attack" – the compressor attack time.

"Release" – the compressor release time. The design of this RMS compressor doesn't support
operation with the release time smaller than the attack time. It such case the release time
becomes equal to the attack time. The same happens when the "Release" knob set to its
minimum "Off" value.

"Knee" – controls the softness of compression curve knee (for gurus).

"Sidechain" – controls high-pass filter in compressor sidechain. Use it to shift frequencies
making the compressor to react in the midrange.

The analog-style indicator shows the signal gain reduction level in dB. Use "12/3 dB" control to
switch the indicator scale.

Typical adjustment steps:

1. Turn on the compressor.

2. If attacks should be passed through, set "Lookahead" parameter to "on", or set it to "off"
if attacks suppressing is needed.

3. Switch indicator to "3 dB" and smoothly reduce "Threshold" until the needle starts to
move a bit (about 0.2 dB).

4. After that don't touch "Threshold" knob but increase "Gain" parameter instead.

5. If the effect of manual "gain riding" is required, slightly change the attack near the
middle knob position. If slower release is required change "Release" parameter to value
greater than attack time.

6. If the aggressive suppressing is required, set "Attack" parameter to minimum value and
"Release" parameter to middle knob position, then smoothly reduce "Release" parameter
to almost equal to "Attack" one. After that slightly increase "Attack" parameter.

7. Adjust the compression ratio by "Ratio" parameter smooth change. Don't avoid low ratio
values such as "1.2 : 1".

8. Adjust the "sidechain" knob if it's necessary to change frequencies used for compressor to
react up to the about 100-150 Hz.

=== 2. "Peak limiter" ===

This module is very aggressive brickwall limiter with very fast attack time (about 0.13 ms) and
very small lookahead (6 samples in 44.1). It was done as the compromise between regular
brickwall limiter and the clipper (i.e. between added distortions and suppressed attack). Also it
was designed to have minimal latency. This limiter intended to limit signal peaks only.

Parameters:

"Peak Limiter" – turns on ("On"), turns off ("Off") the peak limiter or turns it on in stereo-linked
mode ("Linked"). It is convenient to control 3-position switches (like this one) in the GUI by left
and right mouse buttons. Use the left button to move them up and the right button to move them
down.

"Gain" – controls signal level at the peak limiter input.

"Threshold" – controls limiting threshold.

"Mode" – used to select one of peak limiter modes:

– "Brickwall" – the limiter acts as brickwall limiter, e.g. output signal doesn't exceed

the threshold;

– "Soft" – the gain reduction change is softening by filter, as the result the limiter starts

to pass the peaks through that can be suppressed by subsequent modules;
– "M/S" – limiter acts in Mid/Side mode;
– "Multiband" – limiter works in 3-band mode. Crossover frequencies are hardcoded

and the difference between band thresholds is calibrated by pink noise.

"Type" – controls limiter's release time and limiting knee softness:

– "Type A" – the release time equals to the attack time (sounds aggressive);
– "Type I-III" – fixed release time (about 4 ms) is used, the difference between these

modes is in limiting knee: from soft one to hard one;
– "Type C" – separate lookahead used for limiter release (sounds soft).

"Speed" – controls limiter timing:

– "Fast" – normal attack and release times used;
– "1/2" and "1/3" – 2x and 3x longer times used (the limiter reacts 2x or 3x times

slower).

The analog-style indicator shows the signal gain reduction level in dB. To view limiter gain
reduction "Peak/HF" switch should be set to "Peak" position. In "Multiband" mode the indicator
shows maximum gain reduction for all of the bands. The needle speed corresponds to PPM
Type I.

"Amber border" indicator is a helper used to adjust "Threshold" parameter. The peak limiter
in case of continuous limiting starts to distort the sound. To help localize distortions, if the
limiter reduces gain for more than 1 dB longer than 20 ms the amber border appears around
"Threshold" knob. If the border appears for the short time it is recommended to draw attention to
threshold parameter. If the border holds for a continuous time it is recommended to adjust
threshold to less aggressive value.

=== 3. "HF limiter" (a.k.a. acceleration limiter) ===

This module limits the amount of high frequencies in signal. Usually such kind of a limiter used
for vinyl recording to limit the speed of cutting stylus. In this plugin it intended to soften the
sound and make the clipper work more "invisible". Also it can be used as a kind of de-esser.

Parameters:

"HF Limiter" – turns on ("On") or turns off ("Off") this module.

"HF Thresh." – controls HF limiter threshold.

The analog-style indicator shows the reduction of high frequencies in dB. To view HF limiter
operation "Peak/HF" switch should be set to "HF" position.

When this module should be used? Use it in case of "annoying" high frequencies. The
adjustment of this module can be made after the clipper adjustment (see below) to soften the
sound.

Typical adjustment steps:

1. Set gain reduction indicator to "HF" and "3 dB" and turn HF limiter on.

2. Smoothly reduce "HF Thresh." parameter on typical sounding fragment until the meter

needle starts moving a bit (about 0.2 dB). Next increase "HF Thresh." a bit and forget
about this module. If high frequencies become "untypical" this module will limit them.

=== 4. "Oversampled clipper" ===

This module is oversampled clipper with adjustable clipping knee. It can be used either as hard
clipper or as soft clipper. This is the foundation stone of this plugin.

When it should be used? For percussive tracks "Threshold" and "Knee" should be set to affect
only attacks. On other type of tracks this module can be used very subtle when signal should
reach only the beginning of knee zone.

Parameters:

"Gain" – controls signal level at the clipper input.

"Threshold" – controls the clipping threshold (see remark below).

"Upsampling" – controls oversampling type:

– "Off" – oversampling is not used. Use this value in case of high sample rate or when

the clipper used on tracks where aliasing can't make them sound bad. Also it can be

used to reduce CPU usage.
– "4x GR" – 4x oversampling for gain reduction signal is used. It means if gain

reduction is unity the output signal is bit-exact equal to the input signal. This mode

can reduce aliasing and consumes less CPU than "4x signal" mode.
– "4x signal" – 4x full signal oversampling is used. For maximum sound transparency

double precision (64-bit) signal processing used which leads high CPU load. The

mode is recommended to use only on master tracks.

"Knee" – controls the start level of the clipping (the clipping knee). For example if "Threshold"
is set to –6 dB and knee is set to –6 dB the clipping will start from –12 dB and the signal below
is not affected. In rightmost knob position called "Digital" digital clipping is used (see also
"Orange border" indicator).

"Mode" – controls the clipper mode:

– "Normal" – regular mode;
– "M/S" – Mid/Side mode;
– "Multiband" – 3-bands mode (the same as peak limiter "Multiband" mode).

The analog-style indicator shows the signal gain reduction level in dB (e.g. when the clipper
starts to "clip" it actually reduces the level of signal and this reduction is shown on the indicator).
To view the clipper operation set "Clip/ISP protect" switch should be set to "Clip" position. In
"Multiband" mode the indicator shows maximum gain reduction for all of the bands.

"Orange border" indicator. The clipper sounds pretty good in the very beginning of the knee.
When the knee ends and the clipping curve become horizontal the sound quality dreadfully
reduces. This horizontal part of curve leads to "flat tops" of clipping waves and it sounds really
bad. If the knee is set to "Digital" this horizontal zone starts immediately after the threshold but
when used for very short periods of time it can sound acceptable. When the clipper enters to this
"horizontal zone" the orange border around "Threshold" is shown. It allows to control entering
this "horizontal zone" when it is not acceptable and also to control the time of being in this zone.

Remark. In oversampled mode the limited waves don't have "flat tops". Due to that and due to
implementation specific features very short peaks (usually of one sample duration) can exceed
the threshold. If oversampled mode is not used, this effect doesn't happen. Thus when the clipper
operates in oversampled mode additional limiting stage is required (see below).

=== 5. "Output stage" ===

This module contains inter-sample limiter. The real signal curve is calculated across sample
values and true signal level value is analyzed. After that the signal is suppressing in such a way
that true signal level will not exceed the threshold. If such kind of limiting is not needed this
module implements simple digital clipping.

Thereby this module can be used for the following tasks:

1. To limit occasional peaks when the clipper operates in oversampled mode. In most cases

it is enough to use digital clipping with threshold 0.1 dB higher than clipping threshold.

2. To limit true analog signal level (which occurs after the DAC conversion) for those who

really needs it.

3. To act as very cool sounding brickwall limiter (with attack time about 0.5 ms).

Parameters:

"Output" – controls signal level at the module input.

"Ceiling" – controls the limiting threshold.

"Protection" – controls the limiting type:

– "Digital" – digital clipping is used (see "Red border" indicator).
– "ISP Fast" – simplified inter-sample limiter is used. This mode sounds like "ISP

Precise" one but requires less CPU power and doesn't guarantees true signal peaks

limit.
– "ISP Precise" – normal inter-sample limiter operational mode (4x sinc-function

oversampling used to get true signal level).

"Red border" indicator. If digital clipping mode is used and this clipping occurs the red border
around "Protection" is shown. If the border holds for a continuous period of time it is
recommended to reduce the signal level.

Typical adjustment steps:

For the clipper in oversampled mode set "Threshold" parameter to –0.4 dB, "Protection"
parameter of the output stage to "Digital" and "Ceiling" parameter to –0.3 dBFS. Sometimes
"Output" signal level can be boosted from 0 to 0.2 or even 0.5 dB. To soften the sound
"Protection" parameter can be switched from "Digital" to "ISP Fast".

http://vladgsound.wordpress.com
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Great thanks to Dax Liniere for his help!

www.puzzlefactory.com.au

Thanks also to:

Vitaly Zolotarev http://www.vitalymusic.com/
Dean Aka Nekro
Jay Key
Jonas Ekström http://www.mastertone.se/