Polyvox sound effects, rebuilt from the factory list

The factory passport of the Polyvox (Polivoks, Поливокс), the spec sheet that came with every 1982 unit, has a list of things the instrument can do. Next to the musical sounds it names wind, sea surf, gunfire, rain and a steam locomotive. None of them needs anything the panel does not have: a noise source, a filter that can be band-pass, two envelopes that can loop, and one lever that holds the gate open.

Below, each effect is patched in Duovox, our reconstruction, with the plates shown and the knobs that matter playable. Five more follow that the factory did not list: a UFO, a laser zap, a satellite beacon, a landing saucer and a feedback howl. Every one ships in the FX bank under the name used here.

On the 1982 panel, at the bottom right of the amplifier plate, there is a lever marked «ВКЛ.», "on". Vladimir Kuzmin, who designed the instrument, explains in his own account of the project that it sends the gate to every block and starts the envelope generators, as if a key were held down. Duovox labels it GATE ON in Latin lettering and keeps «ВКЛ.» in Cyrillic.

For effects this lever does two jobs. A drone or a noise bed keeps sounding while your hands are on other knobs. And an envelope set to the periodic mode (the ΛΛ icon on its lever) loops for as long as the gate is high, so the sound keeps moving with no key at all. Kuzmin describes that mode too: with sustain at 0, the envelope repeats its attack and decay, and each cycle takes the attack time plus the decay time.

Three of the ten patches here use the lever. The others want a key, because the key press is the event: a shot, a zap, a beep.

Set the MIXER to noise only: VCO I and VCO II at 0, NOISE at 6. On the FILTER plate flip the mode lever to BP, set CUTOFF around 2.7 and RESONANCE around 4.2. Put the ENVELOPE amount at 0, so only the modulator moves the filter. On the MODULATOR plate choose the triangle and turn RATE all the way down. Then bring up the filter's MODULATION knob to about 2.7. Set the amplifier SUSTAIN to 6 and flip GATE ON.

The band-pass is the Polyvox filter's second output: 6 dB per octave on each side of the cutoff, according to the schematic. It takes a narrow slice out of the noise, and the triangle walks that slice up and down. The depth knob decides how far.

On these clips the level swing across a gust grows from 2 dB at depth 0 to about 11 dB at the preset's 2.7. The speed of the gusts is the modulator rate. At MIN it runs at 0.7 Hz in Duovox, one gust every 1.4 seconds. Rate is on a bent curve, as owners describe the original pot: the first half of the travel barely moves it, the top rushes.

Resonance is the difference between air and a whistle. It also changes level a lot: on this player the MIN clip is about 14 dB quieter than the one at 5.1, because a narrow resonant band passes more energy at its peak.

Surf is the same noise without the modulator. Switch the filter back to LP, cutoff around 2.4, resonance low. Now flip both envelope mode levers to periodic, set both SUSTAIN knobs to 0 and give both envelopes a long ATTACK (about 4.3) and a long DECAY (about 4.7). The filter envelope amount goes to 2.4.

Each wave builds over the attack and drains over the decay, then the loop starts again. In the preset a wave arrives about every 2.8 seconds. The filter envelope opens the sound as the amplifier envelope swells it, so the top of every wave is brighter as well as louder. The player turns both decay knobs together.

Measured on these clips, the wave rate goes from about one per 1.1 seconds at 2.7 to one per 3.3 seconds at 5.4. If the two envelopes get slightly different times they drift apart, and the waves stop lining up with their own brightness, which sounds more like a real beach.

One shot is a noise burst through a filter that snaps open. Noise at 6, LP, cutoff around 2.4, filter ENVELOPE at 6 with a short decay (1.8 on the panel) and sustain 0. On the amplifier: attack at MIN, decay 1.8, sustain 0. Every key press is one shot.

For the machine gun, flip only the amplifier envelope to periodic. While the key is held the amplifier loops its short attack and decay, about 16 times a second in the preset. The filter envelope stays one-shot, so the first round is the brightest and the rest settle.

On the rate player the loop rate measured from the clips falls from about 42 cracks a second at 0.9 to about 4 at 3.0.

Rain uses the modulator's fourth shape, sample and hold: noise sampled at the rate you set and held until the next step, so each step is a new random voltage. Send it to the filter and every step lands the band-pass somewhere new. Noise at 5.4, filter on BP, cutoff 3.6, resonance 4.2, filter MODULATION 3.6. The modulator on S&H at 5.3, which is 19 steps a second in Duovox.

The extra ingredient is VCO I as a triangle at 2 feet, the highest range, at 3 in the mixer. It puts a pitched tick inside the hiss.

Slow steps are single drips: at 2.4 the band moves about twice a second. Past 5 the steps run together. Across the player the swing of the clip's brightness shrinks from about 1.3 kHz to 0.9 kHz.

This is the effect that shows off the two looping envelopes best. Noise at 6, LP, cutoff 2.1, resonance 1.8. Both envelope levers on periodic, both sustains at 0. The amplifier envelope makes the chuff: attack 2.1, decay 3.3. The filter envelope loops at a different speed (attack 1.8, decay 3) with the ENVELOPE amount at 3. GATE ON holds it all.

In the preset the amplifier loop runs at about 2.6 cycles a second and the filter loop at about 3.7. Because the two never line up, the bright moments wander across the chuffs. Turn the amplifier loop on its own and the engine changes speed under a filter loop that does not.

The amplifier loop measured from 7.8 cycles a second at 2.1 down to 0.4 at 4.5. To make the train pull away, sweep all four timing knobs from long to short. The clip below does it over eight seconds with the plug-in's own parameter ramps, as you would by hand.

These three use the oscillators instead of noise, and they lean on the modulator's square wave. On the Polyvox that square is unipolar: Kuzmin describes it as positive pulses only. Pitch modulated by it jumps from the played note to a note above and back, a trill, where most synths would wobble around the note.

UFO

VCO I on the triangle at 4 feet, MODULATION 3.9 with the modulator on the square at about 2.6 Hz. VCO II on the square at 8 feet, but at 0 in the mixer: you never hear it directly. Instead its VCO II FM knob on the VCO I plate bends VCO I's frequency at audio rate.

Laser zap

A saw at 4 feet into a low-pass closed almost all the way (cutoff 0.7), resonance up at 5.4, filter ENVELOPE at 6 with a decay around 1.9. Each key throws the cutoff to the top and lets it fall back, and the resonance sings the fall.

Sputnik beacon

A triangle at 4 feet, filter mostly open, the square wave on VCO I's pitch with MODULATION 4.3 and the rate at 4.1, about 6.5 Hz. The deep unipolar trill reads as beeps between two pitches.

The last two take the oscillators away. For UFO Landing, every mixer knob is at 0 and RESONANCE is at MAX, so the filter oscillates by itself and becomes the sound source. A slow triangle (about 1 Hz) on the filter's MODULATION at 3.3 makes it waver, GLIDE at 4.8 slides it between keys, and the rear panel's key tracking is turned up to 80 % so the pitch follows the keyboard more closely than the 62 % default.

Feedback Howl uses the fourth mixer input. On the 1982 unit «ВНЕШ.» (EXT) was an external input on a DIN socket at the back. Duovox has no audio input, so its EXT knob listens to the plug-in's own output instead, the way a patch cord from the output to the input would. The preset has a square at 16 feet at 4.5 in the mixer and EXT at 4.5.

We measured the share of energy that sits off the played note's harmonics on each clip. Up to 5.1 it stays under 1 %. At 5.5 the second note jumps to about 90 %, and at 6 both do. The preset sits just under that edge, so a small move of the knob tips it over.

The player runs the same key pattern through all ten presets, level-matched. Gunfire and Laser Zap come out quieter than the rest because their peaks hit the limit first.

The looping envelopes behind surf and the train get a lesson of their own in the looping envelope, the square-wave trill behind the beacon is in modulator trills, and the sound playground has a player for nearly every knob on the panel.