Synthesizer Programming 2

Synthesizer Programming 2

Now we work with synthesizer polyphony, ring modulation, and the low-frequency oscillator.

We will start from scratch again with SubTractor.

  1. Make a new Reason song file with one SubTractor.
  2. DO THIS: Begin with an Init Patch for SubTractor. (Click on SubTractor, then choose Edit > Reset Device.)

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.

  1. 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.

    SubTractor legato and polyphony controls

    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.

    SubTractor portamento time dial

    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.

Ring Modulation

  1. Ring modulation is a very simple synthesis technique that has been around since the earliest days of electronic music. You take two oscillators and multiply their outputs. The result is a new audio signal that contains frequencies that are the sums and differences of the frequency components of each oscillator. For example, let’s say that both oscillators use a sine waveform (which has only one frequency component, the fundamental). If one oscillator plays 500 Hz and the other plays 100 Hz, then the ring-modulated result will contain 600 Hz and 400 Hz (500 + 100 and 500 - 100).

    Normally, the outputs of the two SubTractor oscillators are added (or mixed) together. If you tick the Ring Mod box, and turn the oscillator Mix knob all the way to the right, you get ring modulation.

    SubTractor oscillator ring modulation setup

    To make this work, the pitches of the two oscillators must be different. Play around with different waveforms and tunings for the two oscillators. Make sure that Osc 2 is turned on!

    DO THIS: Your patch should use ring modulation, with the two oscillator pitches tuned differently and using whatever waveforms you like. Don’t forget to turn on Osc 2 and turn the Mix knob all the way to the right!

Modulation with a Low Frequency Oscillator

  1. 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.

    SubTractor low-frequency oscillator controls

    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.

Control Vibrato with the Modulation Wheel

  1. Use the modulation wheel for its original purpose: to control the depth of modulation. In Part 1 of this assignment, you used the mod. wheel to control the filter cutoff frequency. To make it control the LFO instead, turn up the LFO1 knob next to the mod. wheel.

    SubTractor modulation wheel control governing amount going to low-frequency oscillator depth

    For this assignment, please set the F. Freq knob to its center position, so as to keep the mod. wheel from affecting the filter cutoff frequency.

    The Amount knob in the LFO 1 section functions as an offset, and the modulation wheel changes the LFO depth relative to this offset. To have vibrato only when you raise the mod. wheel, turn the Amount knob all the way down (a depth offset of zero).

    DO THIS: Use the modulation wheel to control the modulation depth, so that when the wheel is all the way down, there is no vibrato.

    NOTE: Some people use the word modulation in a broader way to refer to changes you make to a parameter using any type of control source, not just a cyclical source like an LFO. That’s why SubTractor has a Mod Envelope: an envelope you can use to modulate something else.