Sawtooth Waveform Animator
September 29, 2003
The SWA is the brainchild of Bernie Hutchins, publisher of the Electronotes Newsletter. In 1977, Bernie published his original design of the SWA which is a circuit that inputs a single sawtooth wave and makes it sound like many. The user need only use a single VCO and the animator to simulate the sound of many VCOs all sounding approximately the same pitch.
The SWA consists of several triangle wave LFOs each of which drives an algebraic phase shifter. Each LFO is added in a special way to the original input sawtooth and creates multiple sawtooth flyback points which move backward and forward in time. The result is a waveform that looks and sounds like many sawtooth oscillators which are slightly detuned. In a word, fat.
In 1979, Lester Ludwig improved the design economically by cleverly removing redundant components and also tried to address the problem of controlling the LFO frequencies. Originally, Bernie ran 8 LFOs at 8 widely spaced frequencies in an attempt to make the animator sound good no matter what the input saw frequency. That early design suffered from too much animation at low input frequencies (which sounded vulgar), and too little animation at high frequencies (which sounded thin). Lester added one tunable LFO in an attempt to shift the "weight" of the LFO bank up and down. This sort of works, but it is a manual adjustment.
The Cynthia SWA makes use of a bank of 4 voltage controlled LFOs that respond linearly to the incoming sawtooth frequency. Low input frequencies mean slower LFOs and high frequencies mean faster LFOs - all of them. The result is that the animation aesthetic that you dial in remains constant up and down the pitch range - a major improvement. You can also drive the LFOs with an external voltage, resulting in the totally new technology of voltage controlled animation.
You lucky devils get two separate sawtooth animators in this module which function identically. This description is for half of the module.
The "saw in" jack requires a 5 volt peak-to-peak continuous waveform of some type, preferably a sawtooth, although other waveforms such as triangle or sine will work. Squares and pulses do not work. The input is AC coupled, so the DC offset of the wave does not matter. The saw output consists of the original waveform plus 4 phase-shifted sawtooth waveforms added in, so one oscillator is made to sound like five (by using both halves of the module, you can make one or two VCOs sound like 10!) The apparent detuning of these added waves is a result of the speeds of the 4 LFOs that create them. Turning up the "fat" knob creates more detuning and this detuning will track the frequency of the incoming wave. Turning the "fat" knob all the way down will stop all the LFOs resulting in a frozen, non-animated timbre which will be different every time the LFOs run and stop.
Additionally, three of the LFOs are used to drive three pulse width modulators against the incoming wave which are summed and output at the pulse jack. This triple PWM wave sounds similar to the saw output, but has less amplitude variation and more bottom. It also responds to the fat controls.
You can create dynamic depth animation by using the "VC fat" input jack with its attenuator. A fast acting envelope here can place animation on only the attack of a note. An LFO will result in animation tremelo (for lack of a better name). Experiment, experiment.
Three of the triangle wave LFOs are presented at the A, B, C (and X, Y, Z) jacks for your asynchronous modulating pleasure. Remember, these LFOs will speed up and slow down with the incoming sawtooth frequency, or you can drive them yourself by placing a positive voltage on the "VC fat" input. If the sum of the LFO control voltages is zero or negative, the LFOs will stop as described.
The fattest fat that can be had with this module is by putting the same waveform into both inputs. Set one animator for moderate animation and the other animator for more, then mix the two saw outputs together for pure chainsaw massacre. Try it in stereo!
"It's absolutely clear that this is a world-class timbre fattener"
$ 375.00 US
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