A page about new module designs built into Aries 300 module frames

The Wiard Zero Prototype

Bimorphic Filter Research Prototype

There are so many good filters in the world. I wasn't even sure I was going to make one. A system isn't complete without a filter though. But what new twist can I bring to filter design? One thing I'd like to see is voltage control of filter type. The way this is done is to take the sections of a filter (called "poles") and surround them with a switch matrix so they can be rewired into useful filter types (lowpass, bandpass, highpass and phase shift). An analog to digital converter is used to control the switch matrix, giving voltage control of the type.

This is relatively easy to do, but, the first thing you discover is that using the same filter settings for each type isn't that musically interesting. What's far more interesting is to have two individual filter types, each with it's own settings, and switch between these. The next thought which comes to mind, is what happens if instead of switching between them, we crossfade between them. New filter types are then created by mixing between dissimilar filter setups. Because a mathematical plot of filter design has very different shapes, the unit is named "Bimorphic". Bi meaning "two" and morphic meaning "shapes" = "two shapes".

I have implemented the unit successfully in prototype. While the circuitry is quite complex, it produces very unique sounds.

Tone Source Research Prototype

This module is where I debugged ideas for oscillator design. I wanted to develop a high quality oscillator core board that could be used with many types of waveshaper and wave generator boards. After studying all the available literature until my eyes bled, I arrived at a design that I am quite happy with in terms of features and performance. The oscillator core has these features:

• Twenty octave range with coarse and fine tune controls
• Good thermal stability
• Accurate 1V/Oct. tracking over standard keyboard range
• AC coupled linear frequency control input
• Variable strength synchronization control

To this is added the tone source shaper board. This board is designed to address wave forms in musical terms (harmonic content) rather than technical (wave shape). The section starts with a low distortion sine wave. Two other waveforms are generated, one containing only even harmonics and the other only odd harmonics. A pan control is provided to pan continuously between all even harmonics - both - all odd harmonics. The sine wave fundamental can be blended with this panable mixture under voltage control.

The action of the classical VCO-VCF signal chain is to provide dynamic harmonic spectra under voltage control. A typical transformation is from a waveform with high harmonic content to one with less harmonic content over time. The same effect is produced by dynamically controlling the balance of fundamental and upper harmonics and sounds like a low resonance filter sweep, but different. This, used in conjunction with a filter, can produce new types of sounds where the harmonic density is moving inversely to the filter cutoff.

Faux AR-345 VC Envelope Generator

A PAIA CEM3310 experimenters board wired up as an AR-345 voltage controlled envelope

Mixolator Research Prototype

This module came from combining all the best ideas for VCA design in Electronotes magazine.

The module contains two "Mixolators". A mixolator has the following functions:

• A VCA based around the CA3280 for improved signal to noise ratio over CA3080 designs.
• The VCA response is continuously panable from linear to logarithmic.
• The unit will mix, pan, crossfade or switch any two +20dbv signal inputs.
• Either mixolator can be switch selected to be a ring modulator.

Sequantizer Module Research Prototype

A sequencer is an essential part of a good synthesizer. Because they are fun! I think (at minimum) a sequencer should have these features:

• At least eight stages
• Stage indicator lamps
• Individual gate outputs
• A semi-tone quantizer
• Direct 0-10 V outputs
• A reset input for sequences less that 8 steps

One of the best feature I have seen, and one that is not included in most units, is voltage controlled stage select. The ability to dial in a stage with a knob makes tuning very easy and allows "playing" the unit from the control. Voltage stage select also allows the unit itself to act as a quantizer, so "Sequantizer".

The unit has two types of stage select, a digital counter and a three bit analog to digital converter. Since these are digital signals the normal method would be to "OR" them together which forms a digital "mixer". Instead I have chosen to combine them by "exclusive OR" gates. What happens is that normal order of the digital counter can be permuted by the setting of the A/D converter. This produces different orders of stage selection depending on the setting of the "Select" knob and mimics (in a more controlled fashion) the "Random" switch on an ARP Model 1613.

The use of XOR gate was actually suggested by their use as the ring modulator in the ARP Odyssey. When the "Step" and "Select" inputs are both fed audible rate signals, the equivalent patch is of a signal individually ring modulated by three different octaves of another signal. Quite rich.

Envelator Research Prototype

The envelope generator is probably the most under-rated module in a modular system. People tend to take them for granted, as a "utility" module and not very interesting. Actually,they have more to do with the usability of a system than any other single module.

Unfortunately, the early synthesizers used standard keyboards as controllers and most envelope generator technology is linked to keyboard design. It goes something like this: When a key (on the keyboard) is pressed, the keyboard interface outputs three signals. One is a control voltage corresponding to the position of the key on the keyboard. Another is a fixed voltage level (called a gate signal) indicating that some key is depressed and remaining active until all keys are released. The last is a short pulse (called a trigger signal) which is output when ANY key is depressed. This is used to differentiate between staccato and legato playing. The standard mode is to generate a new trigger pulse every time a new key is pressed, even if the last key has not be released. A switch is often provided to select a mode where a new trigger is generated only if all keys are released before a new one is pressed.

An envelope generator that uses only the gate signal as an input is called an "attack - release" generator and it has logic that works like this: When a any key is pressed, the voltage at the output of the envelope generator rises towards a final fixed voltage, at a rate set by the sum of the front panel "attack" control and an external "attack" rate voltage. If the gate signal goes away before the output reaches the fixed voltage level, the output voltage immediately begins to head back toward zero volts at a rate set by the sum of the front panel "release" control and an external "release" rate voltage. If the gate signal does not go away before the output voltage reaches a fixed level, it will remain at that fixed level until the gate signal does go away and then heads back toward zero volts at a rate set by the sum of the front panel "release" control and an external "release" rate voltage. The portion after the output voltage has reached the fixed voltage and remains there, is called the "sustain" portion of the envelope. Because the "attack" portion is dependent on having enough "sustain" time to complete the attack, the amplitude of the envelope changes when the gate time is less than the "attack" time. This is useful for expressive, legato playing.

An envelope generator that uses only the trigger signal is called an "attack - decay" generator and it has a logic that works like this: If a new key is pressed, the voltage at the output of the envelope generator rises towards a final fixed voltage, at a rate set by the sum of the front panel "attack" control and an external "attack" rate voltage. Since a trigger pulse is very short, there is no "sustain" portion and the "attack" would never complete unless we use some logic gates. We use a simple one bit memory called a "latch". The latch is set (turned on) by the trigger pulse, and generates a signal just like a gate signal, until it is reset (turned off) by some other signal. When the latch is reset, the output voltage immediately begins to head back toward zero volts at a rate set by the sum of the front panel "decay" control and an external "decay" rate voltage. The signal that turns the latch off, could be a number of things, lets take the example of testing to see if the voltage has reached some reference voltage. In this case, the amplitude of the envelope is independent of the duration of the note. This is useful for rapid, staccato playing. Also, the output of the latch itself is useful, since when it goes off, it marks the end of the decay portion.

There are a lot of possible ways to make a circuit that will meet either one of these descriptions. In the case of the "attack - release" generator, a rectifier followed by a simple filter with independent positive and negative going time constants will work. This takes two diodes, two pots, a cap and an op-amp. If we put a circuit on the input that limits the input to 0-+10V we can also feed an audio signal in the gate input and use it as an envelope follower. Since the circuit has a gain of 1, we can feed a control voltage through the gate input and use it as a lag processor with independent up and down portemento times. This is the basis for the envelope generators supplied in the oscillator modules (Waveform City, Classic VCO and Tone Source).

That's fairly simple to do and covers the case of legato playing. But people don't play all legato, nor do they play all staccato. Real human playing style is a combination of both. Ideally we would like to have an envelope generator smart enough to adapt to it's input. Lacking that, we can try to combine the two types of response in some musically useful way. A simple approach would be to start both types of envelopes going at the same time, and be able to mix the two together. Early units did just that through simple pan pots that panned between the two responses. This began the ADSR (attack, decay, sustain, release) envelope generators. Early units were a sub-patch on a modular, but when monophonic synthesizers appeared they needed to save room on the front panels. So the number of controls needed to be cut down.

I have reversed that trend and brought back all the knobs and then some. These envelope generators are intended to be as versatile as they can be made.
Each Envelator:

• Can function as a voltage controllable attack-release or attack-decay envelope generator.
• It can function as a voltage controllable LFO with Triangle, Sawtooth, Square and Pulse waveforms.
• Attack and Decay/Release times are 1V/octave controllable from approx. 1 millisecond to approx. 20 seconds
• Positive and negative going outputs are both provided. Using combinations of feedback, virtually any linear or exponential envelope can be generated.
• An additional output provides voltage controlled panning between the two outputs. This is normally used for the "sustain" portion of ADSR envelopes. If the first section is off and the second section is set to oscillate, it acts as a classic VCO-VCA voice.

Voltage Controlled Votrax Babble Box

Tom Henrys Deluxe VCO circuit with a phase locked Votrax SC-01 Phoneme Synthesizer

PAIA MIDI2CV Interface

John Simontons excellent MIDI to CV converter mounted in an ARies 300 frame, with voltmeter and jack multiples. Binary encoders are used to replace the DIP switch for MIDI channel and Mode.

Digital Noiseshapers

Starting with a basic VCO board add an A/D controlled CD4089 Binary Rate Multiplier and a Buchla Model 266 Quantized Voltage Source