A-126-2 Frequency Shifter

Doepfer A-126-2 Eurorack FREQUENCY SHIFTER Module

Fully analog frequency shifter from Doepfer! Unlike a pitch shifter, which multiplies the frequency of every overtone in a sound by the same ratio (thereby retaining harmonic spread) a frequency shifter will shift each overtone by instead adding to it's frequency, thereby greatly changing the harmonic spread. Frequency shifters are related to AM techniques like Ring Modulation and can be used to create ring mod like sounds and more! When processing a signal, feedback a small amount of the output back into the input for phaser like sounds! Per Doepfer:

Module A-126-2 is a fully analog frequency shifter for audio signals. A frequency shifter is an audio processing unit that shifts each frequency of the incoming audio signal by the same frequency. If the shifting frequency is e.g. 200Hz an incoming audio frequency of 1000 Hz becomes 1200 Hz, 2000Hz becomes 2200 Hz, 3000 Hz becomes 3200 Hz and so on. Pay attention that this is different from pitch shifting where all frequencies are shifted proportional (e.g. 1000>1200Hz, 2000>2400Hz, 3000>3600Hz)

The frequency range of the internal quadrature VCO is about 8 octaves (about 20Hz ... 5kHz). If required an external quadrature VCO can be used.

The module is equipped with these controls, inputs and outputs:

Frequ. 1: first manual control of the shifting frequency (factory setting: coarse, range about 20Hz - 5 kHz)
Frequ. 2: second manual control of the shifting frequency (factory setting: fine)
by means of internal jumpers the sensitivity of Frequ.1 and 2 can be swapped (i.e. Frequ.1 = fine and Frequ.2 = coarse)
the relation between coarse and fine control is about 25:1 (corresponding to about 8 octaves to 1/3 octave)
FCV In (socket) and FCV (small control without knob): control voltage input with attenuator for the external voltage control of the shifting frequency
Mix: manual control of the up/down shift panning unit, fully CCW = down shift, fully CW = up shift, in between a mixture of down and up
Mix CV In (socket) and Mix CV (small control without knob): control voltage input with attenuator for the mixing unit for external voltage control of the up/down mixing
Audio In (socket), Level (small control without knob) and Overload (LED): audio input with attenuator, typ. audio in level = 1Vpp, the level control has to be adjusted so that the overload LED just begins to light up a bit, when the LED is fully on clipping/distortion occurs, when the LED is permanently off the input level is too low and the signal-to-noise ratio increases
Audio Out (socket): audio output of the frequency shifter
Squelch (small control without knob): controls the squelch function: fully CCW (Env.) the output VCA is controlled by the envelope signal, which is derived from the audio input signal, fully CW (open) the output VCA is permanently open (no squelch function), in between the squelch intensity can be adjusted
Quadrature VCO Outputs (sockets Sin and Cos): outputs of the internal quadrature oscillator, about 12Vpp level (+6V/-6V)
Ext. Inputs Sin and Cos (sockets): required when an external quadrature VCO (e.g. A-143-9 with a wider frequency range or A-110-4 with thru zero feature or A-110-6 with different waveforms) is used instead of the internal quadrature VCO, the levels of the external VCO should be about 10Vpp (8...10Vpp are OK) and the signals have to be symmetrical around zero Volts, the sockets are normalled to the internal quadrature VCO (i.e. the sockets are equipped with switching contacts that interrupt the internal connection as soon as a plug inserted)
VCA ext. CV (socket): used when an external control voltage (e.g. from an envelope generator) should be used to control the output VCA instead of the internal squelch unit, the socket is normalled to the output of the squelch control (i.e. the socket is equipped with a switching contact that interrupts the internal squelch connection as soon as a plug inserted). From about +8V external control voltage the VCA is fully open.