A-129 Vocoder Subsystem

no longer available


Working principle of a
the Vocoder

The term vocoder is derived from the words voice and coder. A vocoder is an audio processor that captures the characteristic elements of an an audio signal - normally a human voice - and then uses this characteristic signal to affect another audio signal (e.g. a synthesized sound like VCO or Noise). The technology behind the vocoder effect was initially used in attempts to synthesize speech. The effect called vocoding can be recognized on records as a "talking synthesizer", made popular by artists such as KRAFTWERK. Pioneers of electronic music took this concept and turned the vocoder into what it is now - a tool for creative sound design. The vocoder works like this: The sonic character of the analysis signal - i.e. normally human voice - is extracted and transforms the signal at the vocoder's synthesis input. For this, a set of filters, envelope followers and voltage controlled amplifiers are needed, making good analogue vocoders very expensive.
More detailed the vocoder works like this: The voice signal is fed into the vocoder's analysis input (A-129/1). This signal is sent through a set of parallel filters with successive envelope followers that create a "signature" of the input signal, based on the frequency content and level of the frequency components. The signal to be processed (e.g. VCO or Noise) is fed into the synthesis input of the vocoder (A-129/2) and sent through an identical set of parallel filters with a separate VCA (voltage controlled amplifier) behind each filter. The envelope follower outputs of the analysis section are used to control the VCAs of the synthesis section. The filter signature created during the analysis of the human voice is used to filter the synthesized sound with a frequency responce similar to the voice. Consequently the output of the vocoder contains the synthesized sound modulated by the filter created by the voice. One hears a synthesized sound that pulses to the tempo of the voice with the tonal characteristics of the voice added to it: the synthesized signal "talks".

For most of the standard vocoders the control voltages generated by the analysis section (envelope follower outputs) are connected to the VCA control inputs of the synthesis section. For the modular vocoder A-129 the control voltage outputs of the analysis section A-129/1 and the control voltage inputs of the synthesis section are available as jack sockets. This enables the user to process the control voltages with other modules (e.g. the slew limiter/attenuator/offset generator (see A-129/3 and A-129/4) to obtain functions not possible with a non-modular vocoders. Another advantage of the modular concept is the possibility to exchange or shift frequency bands. And the modular vocoder could be "abused" in many ways, e.g. by controlling, modifying or creating the control voltages with other A-100 modules (e.g. LFOs, S&H, Random CV, Shepard voltages) or even to record the "vocoding" with CV-to-MIDI and MIDI-to-CV interfaces (e.g. A-192 and A-191).

The modules of the Vocoder subsystem A-129

A129-1 A129-2

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Analysis Section A-129/1

Synthesis Section A-129/2

The A-129 series of modules forms a modular vocoder. The basic components are an analysis section (A-129 /1) and a synthesis section (A-129 /2). As mentioned above the vocoder needs two input signals: a voice element which serves as the raw material for the tonal shaping, and is patched into the analysis section; and a carrier signal, which is patched via the instrument input into the synthesis section.
The speech signal is chopped up and analysed in the A-129/1 module, and then combined with the carrier signal in the A-129/2 synthesis section. As a result of this procedure, the carrier signal assumes the tonal character of the speech signal, but with its own pitch maintained.
Since the A-129 is a modular vocoder, and the connections between the analysis and synthesis section are external, using patch-leads, you can use this interface to patch in your choice of modules (eg. attenuator, slew limiter, CV-to-MIDI / MIDI-to-CV interfaces,, inverter, etc.).
There's also the possibility of connecting the frequency bands of the analysis and synthesis sections arbitrarily, so that, for instance, a low frequency band in the speech signal can control a high frequency band in the carrier signal.
The A-129/2 synthesis section can also be used as a stand-alone voltage-controlled filter bank - or in combination with a MIDI-to-CV interface as a MIDI-controlled filter bank.

The A-129/1+2 both use 15 high quality narrow filters: 13 band pass filters, 1 low pass and 1 high pass filter:

Frequency response of the 15 filters used in the A-129/1+2

For more detailed information please look at the English user's manual of A-129/3 and /4: A1291man.pdf

no longer available 

Sound examples

Here some examples that were made with the basic modules of the vocoder system (A-129-1 and -2). For all examples a looped male voice was used as speech input.

In the first example the sawtooth output of a VCO is used as carrier signal. After each cycle the positition of the octave switch is changed:


In the second example a polyphonic carrier is used (four VCOs mixed together in an A-138):


The following example shows the noise signal of an A-118 as carrier:


... and now the 6 Oscillators output of the A-117:


In the last example a polyphonic signal is used again (several VCOs) but the pitch of the VCOs is changed by a sequencer and the number of VCOs is increased (beginning with one, then two, then three)::



The Five-way VC slew limiter / offset generator / attenuators (A-129 /3) and Slew controllers (A-129/4) are particularly designed for this purpose. Module A-129 /3 includes 5-way Attenuators, 5-way Offset Generators, and a Slew Limiter (which works on all the voltages at the five CV inputs simultaneously). Using the A-129 /3 just on its own, two functions are available:

  • Attenuator: whatever signal is patched into the CV input can be attenuated by your chosen amount before being sent to the CV output. The attenuation is set with a control knob.

  • Offset Generator: whatever signal is patched into the CV input will have an offset voltage added to it before being sent to the output. The offset is variable with a control knob.

The Slew Limiter function is only available if the Slew Control Input of the module A-129/3 is controlled by the Slew Limiter Controller A-129/4 (see below).

For the maximum extension of the vocoder three modules A-129/3 are required as the A-129/3 contains only 5 units but the complete vocoder has 15 frequency bands. Usually, the A-129/3 is patched between the CV outputs of the analysis section A-129/1 and the CV inputs of the synthesis section A-129/2. You can also use module A-129 /3, particularly in combination with A-129/4, for other purposes. For example, using the A-129/2 synthesis section only, you can make a filterbank.

Module A-129/3 can also be used out of a vocoder to attenuate any signal in the A-100 and to add a fixed offset voltage (e.g. to expand the features of the dual low cost VCA A-132, the Quantizer A-156 or the Sampler A-112). 

Module A-129/3 is suitable only for the processing of control voltage signals. It cannot be used to process audio signals.

For more detailed information please look at the English user's manual of A-129/3 and /4: A1293man.pdf

no longer available 

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Slew Limiter/Attenuator/Offset Generator A-129/3


To use the Slew Limiter section of the 129 /3, you need to have module A-129 /4 (Slew Limiter Controller) as well. It has several dedicated functions, and gives you control over the following slew limiter functions:

  • Manual control of the slew rate

  • CV control of the slew rate, with an input attenuator

  • Choice of three functions: "Follow", "Slew" and "Freeze"

  • Freezing the output voltages for the duration of a gate

This set of functions is operated by the Slew Limiter Controller, A-129/4. For this the Slew Control Outputs of the A-129/4 are connected to the Slew Control Inputs of up to three A-129/3. 

For more detailed information please look at the English user's manual of A-129/3 and /4 A1293man.pdf.

no longer available 

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Slew Limiter Controller A-129/4


The Voiced / unvoiced detector (A-129/5) can recognise voiced and unvoiced sections in the speech signal, and switch the carrier signal accordingly. The incoming speech signal is processed through a pre-amplifier with adjustable gain and a treble boost unit. The treble boost improves the vocoder effect. The voiced/unvoiced recognition system controls a voltage controlled switch (like A-150) which is used to switch between the voiced and unvoiced carrier signal (e.g. VCO and Noise). Additionally the voiced/unvoiced information is available a a gate signal. A LED displays the unvoiced state.

For more detailed information please look at the English user's manual A1295man.pdf.

no longer available 


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Voiced/Unvoiced Detector A-129/5

A special MIDI-interface for the vocoder system is planned. The basic functions are a 16-way CV-to-MIDI interface and a 16-way MIDI-to-CV interface (way 16 will be used for other functions like controlling slew-rate or voiced/unvoiced). The CV-to-MIDI section converts the CV outputs of vocoder analysis into MIDI controllers which may be recorded by a computer sequencer. The MIDI-to-CV section converts incoming MIDI controller information into CV's for the vocoder synthesis section. Additionally we plan to store some factory and user definable 'vocals' in the MIDI interface so that you may call up complete vocals (like 'a', 'e', 'o', 's', 'sh' and so on) by MIDI program change events (may be we use another MIDI event type for this purpose). Thus the vocoder system will become a universal MIDI controlled filter system not limited to the standard vocoder features.

Overview: Prices / Width / Depth / Current of all A-129-x modules:


Price [Euro]
with red LEDs

Price [Euro]
with blue LEDs

Width [HP / mm]

Depth [mm]

Current [mA]

no longer available 


370.00 (no extra charge)

20 + 12 HP = 32 HP / 101.3 + 60.6 mm

60 mm

+180mA (+12V) / -180mA (-12V)

no longer available 

(has no LEDs)

(has no LEDs)

16 HP / 80.9 mm

60 mm

+40mA (+12V) / -20mA (-12V)

no longer available 



8 HP / 40.3 mm

40 mm

+30mA (+12V) / -10mA (-12V)

no longer available 



8 HP / 40.3 mm

45 mm

+30mA (+12V) / -20mA (-12V)

The price in US$ depends upon the exchange rate between Euro and US$ at the payment day. Free currency converter:
All specifications and prices are subject to change.

A-129/1 und /2 are available only together. 
The additional price for each blue LED is Euro 2.00.
The maximum extension of the vocoder requires these modules: 1xA-129/1+2, 3xA-129/3, 1xA-129/4 und 1xA-129/5.

no longer available