Polyphony and Monophonic Legato Mode

The term polyphony, literally meaning “many voices,” refers in synthesizers and samplers to the maximum number of notes you can play simultaneously.

Early synthesizers, like the Moog modular series, could play only one note at a time — they were monophonic. If you held down one key, and then played another key before releasing the first, the first note would cut off suddenly, and you’d hear the second note alone.

The early synths had a feature that helped you to play a single line expressively: portamento — sliding smoothly from one pitch to the next. Using portamento, if you pressed a key before releasing the previous one, the sound would slide from the first note to the second. You could control the speed of the slide.

You can hear a very clear example of this technique near the end of Emerson, Lake, and Palmer’s song, “Lucky Man,” played on a Moog modular system in 1970.

3. You make a SubTractor patch monophonic by reducing its Polyphony to 1. If you want overlapped notes to run together smoothly, then use Legato mode, rather than Retrig mode.

   

   Retrigger mode is the default; it restarts the envelopes every time you play a note. Legato mode restarts envelopes only when there is a gap between the release of one note and the attack of the next. If there is not a gap, then the pitch changes when you play a different note, but the envelopes continue their progress as if you were still holding down the first note.

   

   To make the pitch slide from one note to the next, use the Portamento knob to increase the amount of time it takes to slide.

   DO THIS: Your patch should be monophonic, with legato mode engaged and a non-zero portamento time.

Modulation with a Low Frequency Oscillator

5. We’ve been using the modulation wheel all along, but what does modulation really mean? Modulation is a cyclical change made to some aspect of a sound. For example, if you modulate the frequency of an oscillator, it means the frequency moves up and down in a repetitive way. If you do this smoothly and slowly, you get vibrato, a characteristic of many different instrumental or vocal sounds. If you modulate the amplitude of an oscillator, then the loudness will fluctuate repetitively — an effect known as tremolo. You could modulate other parameters, such as the cutoff frequency of a filter. Modulation is one of the best ways to create dynamic and animated sounds. To learn more about modulation, run the interactive Modulation app.

   To set up any kind of modulation, you use a control source called an LFO, or Low Frequency Oscillator. This works like any other oscillator, except that the waveform it generates oscillates relatively slowly, at a sub-audio frequency — that is, a frequency below the lowest frequency that humans normally can hear (about 20 Hz). You don’t listen to the LFO output directly; instead you use it to vary some other aspect of the sound that you can hear, such as the pitch, amplitude, or filter cutoff.

   

   Let’s say we want to add vibrato to our SubTractor patch. Use LFO 1 as a control source, and choose as a destination one or both of the audio-rate (i.e., audible) oscillators. Do this by pressing the Dest (destination) button in the LFO 1 panel so that Osc 1,2 lights up.

   You have to turn up the Amount knob to hear any change to the oscillator pitch. This knob controls the depth of modulation — in this case, how much the LFO pushes the frequency of an audio-rate oscillator above and below its offset. The greater the modulation depth, the wider the vibrato. Use the Rate knob to adjust the LFO frequency — the speed of the vibrato. Choose an LFO Waveform. The bottom two waveforms (the ones represented by squiggly lines) are random, rather than strictly periodic. Experiment!

   DO THIS: Your patch should use an LFO to modulate the frequencies of both oscillators. Select any waveform type and any rate for the LFO.