Triple VCO

Triple VCO

the range for the primary oscillator is 10 octaves with an offset range of +2 octaves for osc2 and osc3 adjustable in both quantized semitones and non-quantized values switch selected.

in recent years the pursuit of many analogue synth builders has been towards the development of vcos that achieve accurate pitch tracking, and low drift tuning specifications. this has been seen as the holy grail of vco design in answer to the complaints of users unhappy with drifting pitch especially problematic during live performance. it is now commonplace to have highly stable oscillators with excellent tracking over a wide range.

an unfortunate side effect in this pursuit of perfection is that some users find the results "sterile" sounding and lacking in musicality when compared with early vco contributions from Moog and EMS etc.

there is nothing inherently "sterile" when comparing a single cycle waveform like a sawtooth from one vco to the next. a sawtooth is a sawtooth no matter how it is generated. it would require a considerable amount of distortion to the basic ramp shape to change the sound significantly. none of the older vcos do this in a meaningful way. it is more likely a consequence of subtle tuning errors that creates this perception of warmth in older designs. the "beating" effect of several vco signals shifting phase against each other can provide a pleasant animation to a patch particularly if concentrated in the bass notes and to a lesser extent in the higher frequencies.

a small amount of linear detuning has been added to the exponential pitch control of oscillators 2 and 3 when quantize switch is set to off or osc1 in an attempt to replicate the animation effect mentioned above. it is disabled in the all position.

another tuning related issue with early vcos which could be attributed to noisy power supplies, temperature drift and a host of other sources, produces minor deviations in tuning frequency over time equivalent to a slow random modulation of pitch. the resulting subtle pitch wobble effect is regarded as a possible ingredient for simulating the sound of early vcos. the perceived by-product of drifting pitch in a multi vco configuration is also related to "phase beating" and can contribute subtle tonal variation between notes in a sequence or add complexity to sustained notes. a small amount of random modulation applied to the phase of vcos two and three, if pitched higher than the fundamental vco, can add color to the sound without adversely affecting the perceived fundamental pitch and precise tracking of the main vco. the triple osc adds a smooth cosign interpolated random noise modulation to simulate this effect. not easily generated by external methods (unless you have a quad lfo 61b).

triple vco features:
three wide range vcos in one module.
100khz sample rate 16bit sawtooth,triangle, sine and pulse wave forms with band-limited alias-suppression
pulse width modulation control by cv
built-in vca with cv control
wave pairs available on separate outs
20hz-10khz range in hi mode-10 octave range. 0097hz-10hz in lfo mode-10 octave range
on-board 3way vco mixer with both knob and cv inputs. mix is scaled so volume is same for 1 or 3 vcos
3 quantization modes: 1.off, 2.vco1 only, 3.all 3 vcos. modes 1 and 2 add the tuning effects discussed above.
unique hard sync function allows vcos to sound even when master frequency is greater than slave.
crystal tuning stability with +/-0.005% pitch tracking accuracy over 10 octaves.
switch selected semi-tone quantizer built-in
12hp wide approx. 1" deep
firmware by Bruce Duncan

specs:
frequency range: 10 octaves
10hz-10khz
output: +/-5v or 10vpk-pk @1kohms
input cv 0-10v @100kohms
current: 80ma@+12v, 10ma@-12v

http://modcan.com/emodules/triplevco.html