Doepfer A-125 VC User Manual

doepfer
System A - 100
1. Introduction
VC Phaser
A-125
Level
CV
Audio
In
CV 2
CV
Audio Out
A-125
VCP
Shift
Resonance
Mix
Module A-125 (VC Phaser) is a voltage controlled phase shifter.
Other parameters which can be controlled are reso- nance (governing the depth of the comb filtering, and tonal color - see page 3) and original signal which is added to the phase-shifted signal).
(the amount of the
mix
1
A-125
VC Phaser
System A - 100
doepfer
2. VC Phaser - Overview
A-125 VCP
VC PHASE SHIFTER
Audio In
0
0
CV
0
0
Audio Out
0
Level
10
Shift
10
10
Res.
10
Mix
10
CV
Controls:
1 Level : Attenuator to control the level of the
signal at input
Shift : Control for manually setting the
2
!
amount of phase shift
: Attenuator for the phase shift voltage
CV
3
control signal at input
: Resonance control
Res.
4
Mix : Control for setting the amount of the
5
"
original signal added to the phase­shifted signal
In / Outputs:
Audio In : Audio input
!
" CV : Input for pitch-shift voltage control
Audio Out
§
: Audio output
2
doepfer
System A - 100
VC Phaser
A-125
3. Basic principles
The phasing process relies on dynamic comb filtering. The comb filtering produces a series of gaps in the audio spectrum (in Fig. 1, at 200 Hz, 1 kHz and 5 kHz), by the cancelling process which is created byha­ving identical sounds 180° out of phase with each other (or ‘inverted’).
10k
20k
ÖÖÖÖ
50
100
200
500
1k
2k
5k
Frequenz [Hz]
Fig. 1: The principle of phasing
These zero points are continuously swept through the audio spectrum, cancelling out different frequencies, and producing the characteristic phasing sound.
The principle can be explained by looking at the dia­gram (Fig. 2) of a phaser created by three band pass filters. Here, audio is input to the three filters BP1 to BP3 (notch filters also work), set to different middle frequencies. A slow LFO modulates the frequencies.
The outputs of the band pass filters are then mixed with the original signal. Because of the phase reversal inherent in the filter design (most apparent close to the middle frequency), different areas of the audio spectrum are cancelled out.
Audio In
BP 1
f = x Hz
c
BP 2
f = y Hz
c
Mixer
Out
LFO
BP 3
f = z Hz
f ~ 3 Hz
: A phaser model using separate modules
Fig. 2
c
3
A-125
4. Controls
VC Phaser
System A - 100
1 Level
Attenuator 1 controls the level of the input signal.
doepfer
5 Mix
Use control 5 to determine the exact balance of phase-shifted and original signal. From minimum to maximum produces the following:
2 Shift
Phase shift amount is controlled with this knob, in a
range from around 0° to 180°.
3 CV
As well as manual phase shifting, a control voltage at input " can modulate the shift. Attenuator 3 sets the level of voltage control.
As a rule, a slowly changing signal (eg LFO, ADSR, Random, etc.) is used for this modulation.
4 Res.
This knob controls the resonance - the amount of the output signal fed back to the input. With this you can control the exact depth of the signal cancellation (see Fig. 1). The resonance parameter controls the tone­colour of the sound; you can’t use resonance to make the phaser self-oscillate like on a VCF.
4
Mix = 0 : just phase-shifted signal - "phase / vibrato": the signal sounds somehow skewed.
Mix = 10 : 50% phase-shifted + 50% original signal
- phasing: typical swooshy phaser sound.
P
Try out different settings for resonance and mix, to see how what effect these parame­ters have on the sound.
doepfer
System A - 100
VC Phaser
A-125
5. In / Outputs
! Audio In
Socket ! is the phaser’s audio input.
" CV
The control voltage for modulating the speed of phase shifting is input at socket ". You can set the level of this CV with control 3.
§ Audio Out
Output § has the mix of phase-shifted and original signals determined by the position of control 5.
6. User examples
Standard set-up
Fig. 3 shows a typical patch, with various alternative sources of slow-changing modulators affecting the speed of the phase sweep.
LFO
ADSR
Random
S&H
A-190
CV 2
Audio In
1 2
3 4 5
alternativ
Audio Out
Level
CV
Audio
CV 2
CV
Audio Out
In
A-125
VCP
Resonance
Shift
Mix
Fig. 3: Typical phaser application
5
A-125
R
VC Phaser
System A - 100
doepfer
The phaser is simply inserted in the audio path like this. For modulation sources, you could use, for instance, any of the following:
Alter-
native
P
Module Adjustment Effect
1
2
3
4
5
LFO
A-145
ADSR
A-140
Random
A-118
S&H
A-148
A-190
CV 2
With the last two of these alternative modula­tors particularly, you can optionally use an A-170 Slew Limiter after them, to smooth out sudden jumps of control voltage, and make the phasing transitions less abrupt.
low frequency (< 2 Hz)
slow envelope keyboard-
slow random rate
any MIDI con­troller for CV 2 (eg. velocity)
free-running phase-shift
controlled phaser
random phasing
random phasing
MIDI - controlled phasing
"Stereo"-Phasing
Using two A-125s and the patch in Fig. 4 you can create a wide pseudo-stereo phasing effect, with inver­ted signals coming out of each of the two audio channels (Out
Typically, you can use a slow LFO to provide the modulation for the phase shift, but any other modulator will work, as with standard phasing. Phaser VCP 1 is fed the modulation from the LFO directly, while an A-175 voltage inverter is patched in before the second phaser VCP 2, to invert the modulation.
Audio
In
: "Stereo" phasing
Fig. 4
und OutR).
L
LFO
VCP 1
Out
CV
A-175
CV
VCP 2
Out
L
6
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7. Patch-Sheet
System A - 100
VC Phaser
A-125
The following diagrams of the module can help you recall your own Patches. They’re designed so that a complete 19” rack of modules will fit onto an A4 sheet of paper.
Photocopy this page, and cut out the pictures of this and your other modules. You can then stick them onto another piece of paper, and create a diagram of your own system.
Make multiple copies of your composite diagram, and use them for remembering good patches and set-ups.
P Draw in patchleads with colored
pens.
Draw or write control settings in the little white circles.
A-125 VCP
VC PHASE SHIFTER
Audio In
10
0
10
CV
Audio Out
0
10
0
10
0
10
0
Level
Shift
CV
Res.
Mix
A-125 VCP
VC PHASE SHIFTER
Audio In
10
0
10
CV
Audio Out
0
10
0
10
0
10
0
A-125 VCP
Audio In
Level
Shift
CV
CV
Res.
Audio Out
Mix
VC PHASE SHIFTER
Level
10
0
Shift
10
0
CV
10
0
Res.
10
0
Mix
10
0
7
A-125
VC Phaser
System A - 100
doepfer
8
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