The SN-Voice Project: Applications and Operations
Applications
The SN-Voice would make a dandy module for your synthesizer - it supplies two VCO waveforms, a sweepable noise generator, and two different control voltage signals. It also reacts to signals from your synthesizer, keyboard, midi-to-CV converter, joystick, touchstrip, earthquake detector or windmill.
Or, perhaps you would like to turn it into a stand-alone unit in its own right - a sort of cigar box synth,if you will. Or, perhaps, marry it to a small keyboard and make a mini-synth out of it. The SN-Voice can be operated without one, but it does lack a voltage controlled filter, so you if you plan to make a stand-alone synth out of it, you might consider choosing a design for that - there are a number of filters out there that not only would work quite well, but perhaps give your SN-Voice based contraption a personality of its own. How about a Magic Smoke Thomas Henry Mankato, a Ray Wilson State Variable or 24 dB low pass, a Ken Stone Steiner Synthacon or a René Schmitz Late MS-20? Another device I've found to be very effective with it is Ken Stone's CGS29 Wave Multiplier. Route the SN-Voice VCO triangle wave through it, and control it with the LFO or EG signals. The variation in timbre can be quite astounding.
Perhaps one may even want to add an additional VCA, or a simple sample and hold. Or just put the circuit in as it is without any addition at all - it can do quite a bit on its own. If you've got a modular synth or a Ray Wilson Sound Lab, it can be interfaced just fine with those devices.
For more info on the devices mentioned above, visit these links:
SN-Voice Operational Blocks
In order to understand operation of the SN-Voice, it helps to remember that there are four main sections to it:
| The Voltage Controlled Oscillator (VCO) | The VCO provides two separate outputs - a fixed amplitude triangle wave and an EG controlled variable or fixed square or pulse width modulated wave. |
| The Voltage Controlled Noise Generator | The noise generator supplies a sweepable digital noise signal that shares an output connector with the Square/Pulse Width Modulated VCO output. Its amplitude can be EG controlled or fixed. |
| The Low Frequency Oscillator (LFO) | The LFO provides a manually controlled variable frequency triangle wave output and is normalled to provide linear frequency modulation to the VCO. |
| The Envelope Generator (EG) | The Envelope Generator controls amplitude of the Square/PWM VCO and Noise outputs and provides an external EG signal as well. |
The VCO: Controls and Connectors
| VCO Coarse Tune Control | The VCO Coarse Tune Control allows you to tune the VCO throughout the output frequency range of the SN-Voice VCO (0 to approximately 7.5 kHz). This control affects both the square and triangle wave outputs of the VCO. This control is used to set the general initial frequency. |
| VCO Fine Tune Control | The VCO Fine Tune Control allows you to tune the intial VCO frequency over a much narrower range than the VCO Coarse Tune Control. This is useful setting the operating frequency of the VCO to an exact point. |
| 1V/Oct Input Jack | The 1V/Oct Input Jack is the main VCO frequency control voltage input, and is generally intended to be connected to a keyboard, sequencer or other control device that is used to generate musical intervals. A control voltage at this input will increase the frequency of the SN-Voice VCO as the input CV is made more positive and decrease the frequency of the SN-Voice VCO as the input voltage is made more negative. The frequency response is 1V/Oct. In other words, the VCO frequency with a 2V input will be one octave higher than the VCO frequency with a 1V input at this input. There is no level control for this input. |
| EXP FM Input Jack | A control signal applied at the EXP FM Input Jack provides the same type of exponential response as the 1V/Oct input, with the difference being that the applied control signal passes through the EXP FM Level Control. The EXP FM Control allows you to alter how much of an effect the control voltage at this input will have on the SN-Voice VCO frequency. This input is generally intended to provide frequency modulation to the SN-Voice VCO. A medium slow LFO (around 7.5 Hz) will provide a pleasing vibrato to the VCO frequency when applied to this input. An audio rate signal can be used to produce FM effects when applied to this input. An envelope generator applied to this input can shift the frequency of the VCO with each note. There are other control sources that can be used here, but you get the picture. |
| Linear FM Input Jack | A control signal applied to Linear FM Input Jack will control the SN-Voice VCO in a linear manner. The frequency response to this voltage is a V/Hz function. As opposed to the V/Oct response of the 1V/Oct and EXP FM inputs, this voltage does not double the frequency for each additional volt of input, but rather increases or decreases the VCO frequency a fixed amount of Hz for each volt applied. Because the human ear is trained to discern changes in frequency on an exponential scale, this type of response, though linear, will appear to the human ear as having less effect for a given control voltage level at higher frequencies than it does at lower frequencies. The Linear FM Control allows you to alter how much of an effect the control voltage at this input will have on the SN-Voice VCO frequency. Like the EXP FM Input, this input is generally intended to provide frequency modulation to the SN-Voice VCO. Because of the difference in response, a different effect will be discerned for a given control signal when applied to this input in comparison to applying the same signal to the EXP FM Input Connector. Linear audio FM has a distinctly different flavor than exponential audio FM. Slower modulation, as in the range of vibrato, will have a more pronounced perceived effect at lower frequencies than higher frequencies. One additional note: the SN-Voice LFO is normalled to this input. In other words, if no plug is inserted into the Linear Modulation Jack, the LFO signal is applied to this input. Inserting a plug from a patch cable into this connector automatically switches the LFO signal from the input and applies whatever signal is on the plug to the input of the linear modulation circuit instead. |
| Linear FM Level Control | The Linear FM Level Control allows you to adjust how much of an effect the control signal applied to the Linear Modulation Input Jack will have on the SN-Voice VCO frequency. This allows you to control the depth of modulation the linear FM signal will provide. With the Linear Modulation Level Control set full CCW, the signal applied to the Linear FM Input Jack will have no effect on the SN-Voice VCO frequency. As the control is rotated CW, the signal will have an increasingly greater effect on the VCO frequency, until at full CW, the effect will be at maximum. The Linear FM Level Control is actually a sort of dual purpose control. As mentioned in the Linear FM Input Jack description, the SN-Voice LFO is normalled to the Linear FM Input Jack. This means that, if no plug is inserted into the Linear FM Input Jack, the SN-Voice LFO is fed automatically to this input. In this case, the Linear FM Control allows you to control how intensely the SN-Voice LFO will modulate the frequency (or not modulate it at all). In other words, this control allows you to add linear vibrato to the SN-Voice without using a patch cable! |
| Linear FM AC/DC Switch | The Linear FM AC/DC Switch allows you to either AC couple or DC couple the signal applied to the Linear FM Input Jack. AC coupling removes the DC component of the input signal - in other words, if a fixed voltage is applied to the Linear FM AC/DC switch while the switch is in the AC position, that constant voltage will have no effect on the SN-Voice VCO frequency. If the voltage is AC, I.E. changing in voltage, the change in voltage will affect the frequency of the VCO. A slow moving, smoothly changing signal, such as a triangle LFO will have less and less effect the lower in frequency the LFO oscillates and greater effect the faster the LFO oscillates. Quickly changing components in slow moving LFO signal, such as the rising and falling portion of a pulse wave will effect the VCO frequency more greatly while the fixed component of the same signal (the 'horizontal' DC component of the signal) will have no effect. Applying a pulse wave LFO to this input while it is AC coupled will cause a spike upward in frequency, then a spike downward in frequency, at the rate of the LFO. Placing the Linear FM AC/DC Switch in the DC position allows both DC and AC signals to affect the SN-Voice VCO in a linear fashion. The main intended purpose of this control is to provide a variation in audio rate linear FM of the SN-Voice VCO - AC coupling the input audio signal will result in a different effect than if the signal is DC coupled. As demonstrated above with the pulse wave example, it is a potential source for interesting non-audio rate modulation as well. |
| Triangle Output Jack | The Triangle Output Jack outputs the SN-Voice VCO triangle waveform at a constant level of 10 Volts Peak to Peak, centered about ground. This waveform does not pass through the internal SN-Voice VCA, and is unaffected by the SN-Voice envelope generator. The frequency of this output is 0 to approximately 7.5 kHz. |
| Pulse/Noise Output Jack | The type and amplitude of the signal present on the Pulse/Noise Output Jack is determined by settings of the following SN-Voice Controls:
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Voltage Controlled Noise Generator: Controls and Connectors
| Initial Noise Frequency Control | The Initial Noise Frequency Control determines the initial frequency of the clock that drives the Digital Noise Generator. This control will manually sweep through the entire range of the Digital Noise Generator, from a random blip every second or so to a high frequency noise. The sweep itself is quite filter-like in its sound. |
| KBD Input Jack | The KBD Input Jack accepts a voltage that controls the noise clock in an exponential manner. This input is intended for use in the same manner that the 1V/Oct input of the VCO - a keyboard or other stepped musical device can produce satisfying intervals of control. |
| VC Noise Input Jack | The VC Noise Input Jack provides the same type of exponential response as the KBD input, with the difference being that the applied control signal passes through the VC Noise Level Control. The VC Noise Level control allows you to alter how much of an effect the control voltage at this input will have on the SN-Voice noise generator frequency. |
| VC Noise Level Control | The VC Noise Level Control allows you to adjust how much of an effect the control signal applied to theVC Noise Input Connector will have on the SN-Voice noise generator frequency. As with the EXP FM Level Control's effect on VCO frequency, this control allows you to control the depth of modulation this signal will allow on the SN-Voice Noise Generator. With the VC Noise Level Control set full CCW, the signal applied to theVC Noise Input Connector will have no effect on the SN-Voice noise generator frequency. As the control is rotated CW, the signal will have an increasingly greater effect on the VCO frequency, until at full CW, the effect of the control voltage will be at maximum. |
| Noise Filter Control | Before the noise generator signal is routed to the output, it passes through the digital noise filter. The digital noise filter is a variable bandwidth low pass filter. The setting of the Noise Filter Control determines the cutoff frequency of this filter. This control allows you to manage the timbre of the noise generator. The range of the filter is from 2700 Hz to 270 kHz. With the Noise Filter Control set to full CCW, the cutoff is at the lowest frequency (2700 Hz). Turning the Noise Filter Control CW steadily increases the cutoff frequency of the noise filter until it is at maximum cutoff (270 kHz) at the full CW setting. |
LFO: Controls and Connectors
| LFO Rate Control | The LFO Rate Control is used to manually vary and set the frequency of the SN-Voice LFO signal. It is used in conjunction with the LFO Range Switch. The LFO Range Switch determines the range of LFO frequency the LFO Rate Control will adjust. Setting the LFO Rate Control full CCW will provide the slowest rate available for the selected LFO range. Turning the LFO range control will increase the frequency of the LFO until the LFO Range Control is at the full CW position, whereupon the LFO frequency will be at the maximum frequency of the selected LFO range. |
| LFO Range Switch | The LFO Range Switch sets the general operating frequency range of the SN-Voice LFO. The LFO Rate Control will vary the LFO frequency within the range set by the LFO Range Switch. There are three positions to the LFO range switch: Low, Mid and High. Setting the LFO Range Switch to the Low position allows the LFO Rate Control to vary the LFO frequency from just below .2 Hz to just above 2 Hz. Setting the LFO Range Switch to the Mid position allows the LFO Rate Control to vary the LFO frequency from just below 2 Hz to just above 20 Hz. Setting the LFO Range Switch to the High position allows the LFO Rate Control to vary the LFO frequency from just below 20 Hz to just above 200 Hz. |
| LFO Output Jack | The LFO Output Jack provides the LFO signal to the outside world. The LFO signal is a triangle wave at 10V peak to peak, centered about ground, at the frequency selected by the LFO Rate Control and LFO Range Switch. |
Envelope Generator: Controls and Connectors
| Gate Input Jack | The Gate Input Jack is used to control the SN-Voice envelope generator when the Envelope Lock Switch is not set to 'Lock'. The Gate Input Connector accepts +5V gate signals from any source, such as a keyboard or sequencer clock. It is also capable of accepting gate signals from a 10VP-P, centered about ground, pulse or square wave LFO. Using an LFO signal provides a method to continually and rhythmically gate the SN-Voice. Varying the pulse width of such an LFO allows varying 'on time' of the envelope generator. When the EG is not locked, a gate signal rising to +5V will gate the EG on at the rate set by the Attack Control. The EG signal will rise to +5V and remain at +5V until the gate signal goes low. Once the gate signal goes low, the decay portion of the EG will begin and the ouput of the EG will drop to 0V at the rate set by the Release Control. The Envelope Generator controls the amplitude of the Noise or Square/PWM signal present at the Noise/Square Connector, and also generates the envelope generator output signal present at the Envelope Output Jack. |
| Envelope Lock Switch | The Envelope Lock Switch provides a means to lock the SN-Voice envelope generator at its highest output (+5V). When the Envelope Lock Switch is set to 'Lock', the envelope generator is held high and any signal applied to the Gate Input Connector is ignored. In the locked mode, the selected signal present at the Noise/Square Output Connector is held constantly on, and the signal present at the Envelope Output Connector is a constant +5V. If the Envelope Lock Switch is not set to 'Lock', the gate signal applied to the Gate Input Connector controls the envelope signal, as set by the Attack Control and the Sustain Control. |
| Attack Control | The Attack Control adjusts the time it takes for the SN-Voice envelope generator to rise from full off (0V at the Envelope Out Jack) to full on (5V at the Envelope Out Jack) when the signal at the Gate Input Jack switches from 0V or below to +5V. With the Attack Control set at full CCW, the attack time is shortest. As the Attack Control is rotated towards CW, the attack time becomes increasingly greater. When the Attack Control is full CW, the maximum attack time of approximately 6.5 seconds is attained. If the gate signal goes low before the attack cycle has completed, the envelope generator will fall to 0V from its current level at the rate set by the Release Control. |
| Release Control | The Release Control adjusts the time it takes for the SN-Voice envelope generator to drop from full on (5V at the Envelope Out Jack) to full off (0V at the Envelope Out Jack) when the signal at the Gate Input Jack switches from 5V or to 0V or below. With the Release Control set at full CCW, the release time is shortest. As the Release Control is rotated towards CW, the release time becomes increasingly greater. When the Release Control is full CW, the maximum release time of approximately 6.5 seconds is attained. If the gate signal goes high before the release cycle has completed, the envelope generator will again rise from its current level to +5V at the rate set by the Attack Control. |
| Envelope Output Jack | The Envelope Ouput Jack provides the SN-Voice envelope generator signal to the outside world. Its amplitude is 0 to +5V. When the EG is locked, this signal remains at a constant +5V. |
A Word About Expected Control Voltage Input Levels
The SN-Voice Control Voltage inputs can all tolerate -5V to +5V inputs.
Thomas arranged the Voltage Controlled Noise generator inputs so that a wide range of signals could be used with it. This was done in anticipation of varying level standards from various devices, as well as providing headroom for inverted control signals (for example, an envelope generator operating with it's 'off voltage' at +5V and 'on' voltage at 0V).
As mentioned before, the envelope generator gate operates on 0 to 5V gates, but a pulse wave signal operating at -5V to +5V will also gate the envelope generator - internally, the SN-Voice simply 'chops off' the range of voltage from below 0V to -5V.
