A-100 Patch Examples

Random Melody

This patch creates an automaticially random melody. The sound source is a VCO (A-110) that is processed by a VCF (A-108 in this example but each VCF or VCA will work). The quantized random control voltage for the VCO is generated by the A-118 random output that is processed by one of the A-129/3 Attenuator/Offset Generator and the lower section of the A-156 Quantizer. The rate of change is controlled by the Rate control of the A-118. The basic tone/note is adjusted by the offset control of the A-129/3 and the spread (distance between high and low notes) by the attenuator control of the A-129/3. The setting of the three switches of the A-156 define the type of the random melody (all semitones, only minor or major scale, only tones from chords and so on). The trigger output of the A-156 is used to trigger the A-140 envelope generator for the filter. It is possible to synchronize the patch e.g. with a sequencer. For this the trigger input of the A-156 has to connected to the main clock source.

Sequenced Wavetables

In this patch the two potentiometer rows of the A-155 sequencer are used to control the pitch (upper row) and the momentary wavetable (lower low) of an A-112 Sampler/Wavetable Oscillator. And this is how it works:
The rectangle output of the A-145 LFO generates the Clock for the A-155 sequencer (any other clock source will work as well) . The A-155 CV output of the upper potentiometer row is connected to the pitch CV input of the A-112. The A-155 CV output of the lower potentiometer row is connected to the CV input of the A-112 that is used to address the wavetable. The A-112 has to be in the wavetable play mode (the picture above does not show the correct settings of the three switches, the upper switch has to be in the S1 or S2 position, the middle in the Play position, the lower in the Wav Position). The Gate-Input has to be connected to as positive signal (e.g. an unused output of an A-165 or A-176) so that the A-112 is permanently triggered (not shown). The audio output of the sampler is processed by a filter (the A-124 Wasp filter in this example, but any other VCF or VCA will work too). The envelope for the VCF is generated by a A-142 Voltage Controlled Decay (any other envelope generator will work too). The trigger for the A-142 comes from the upper Trigger section of the A-155. The Decay is modulated with the Gate row of the A-155 so that shorter or longer longer decays can be controlled with the gate switches. It is not necessary to load the A-112 sampler with wavetables. One obtains very interesting sounds even with a normal sample (e.g. a recorded human voice) that is chopped by the A-112 in the wavetable mode. For each step of the sequence another section of the sample (defined by the lower sequencer row) is cutted out and looped. With the scaling control the spread of the addressed wavetables can be limited. The patch can be expanded e.g. by an A-129/3 to define the position (offset) and spread (attenuation) of the wavetables.

Toggling Sample&Holds

This patch was inspired by the Buchla 266 Source of Uncertainty (SOU). It shows how the sample&hold function of the 266 can be emulated with A-100 modules. And this is how it works:
The incoming trigger signal (rectangle output of an A-145 LFO in this example) is divided by the A-160 clock divider. The /2 output is used to trigger the upper section of the A-148 S&H. The /2 output is inverted by the A-165 trigger modifier and the inverted signal triggers the lower S&H. For both inputs the same voltage source  is used (random output of an A-118 in this example). At the two S&H outputs of the A-148  the random voltage of the A-118 is "stored" alternately. This is the same function as the alternating S&H outputs of the Buchla 266 (the normal CV out of the 266 works as a normal, non-alternating S&H). Even the alternating pulse outputs of the 266 are available (i.e. the /2 output of the A-160 and the inverted output of the A-165). Of course another trigger source (instead of the A-145) and/or another voltage source (instead of the A-118) is possible. We think about a module that integrates all functions of this patch within one unit - provided that there are sufficient inquiries for such a module. 

Additional "emulations" of the Buchla 265/266 Source of Uncertainty (SOU) will follow soon. The integrator section of the 266 is nothing but the Voltage Controlled Slew Limiter A-171. Only the "Quantized Random Voltages with 2ⁿ and n+1 states" and the "Stored Random Voltages with adjustable probability distribution" could be emulated with already existing A-100 modules (as of December 2003). This is why the A-149-1 Quantized/Stored Random Voltages was developed.

New: The toggling S&H function can be realized much easier with the new module A-152 Voltage/Clock addressed Switches/S&H (available ~ summer 2004).

Fluctuating Random Voltages

This is another patch inspired by the Buchla 266 Source of Uncertainty (SOU). It shows how the "Fluctuating Random Voltages" of the 266 can be emulated with A-100 modules. And this is how it works:
The random output of the A-118 Noise/Random source is used to modulate the frequency of the A-147 Voltage Controlled LFO. The basic frequency of the A-147 (i.e. without CV coming from the A-118) has to be about 100Hz to emulate the Buchla 266. The triangle output of the A-147 becomes more or less "noisy" as the random voltage modulates the frequency. Use short random rates (Rate control of the A-118 in the left area). The "noisy triangle" is fed into the lower section of the A-148 Dual S&H. The S&H is triggered by the rectangle output of a second A-147. The output of the S&H is smoothed by the A-171 Voltage Controlled Slew Limiter. In the Buchla 266 the trigger sampling frequency and the slew time are controlled by only one knob. This is why the A-176 is used to generate one common voltage to control both the second A-147 and the A-171 simultaneously. If the simultaneous control of both functions is not necessary the A-176 can be omitted and both the second A-147 and the A-171 can be replaced by a "normal" A-145 LFO resp. a "normal" A-170 slew limiter (upper section). Another modification - if no A-147 is available - is to mix the triangle output of a normal A-145 LFO with the random voltage of the A-118 and to use this mixed signal as S&H input. But in this case an additional A-138 mixer is required.
The advantage - or disadvantage (depends upon your point of view) - of this patch compared to the original 266 is that one has more controls available than the 266. The disadvantage is that you need six modules. We think about a module that integrates all functions of this patch within one unit - provided that there are sufficient inquiries for such a module.
We may develop a separate module (A-149-3 ?) for the "Fluctuating Random Voltages" if there is sufficient need for such a module. In the meantime the above patch will solve the problem.

Chaotic patch based on the so-called logistic equation X_n+1 = k*(X_n  - X_n²) with k = 3.57 ....4.00. The X_n²  term is realized with the first VCA (A-130) by feeding both the CV and signal input with the same signal coming from the S&H output (A-148). The subtraction is made with the voltage inverter (A-175). The S&H is used to sample the last voltage X_n that is used to create the new voltage X_n+1. It is triggered by a voltage controlled LFO (A-147) that determines the rate of the system (controlled by the external Rate CV). The second VCA is used in combination with the A-136 to create the factor k (3.57 ... 4). As the max. amplification if ~1 for the VCA an additional amplifier has to be used (A-136 with a fixed amplification  ~ 4). Even a modified VCA (with modified max. amplification >4) or a VC polarizer (with modified max. amplification >4) could be used. The graphs below show the results for 3 different settings of k.

(attention: so far the patch is theory only, i.e. we did not yet try this patch, comments are welcome to hardware@doepfer.de)

Vocoder with triggered vocal freezing, coming soon .....