In GarageBand I'm using a software instrument called "Screamlead" which has several knobs as follows:

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Some of these, like "glide" and "overdrive," remind me of adjustments on synthesizers. Is "harmonic" also a synthesizer specific adjustment? Or is does it apply to software instruments more generally? What exactly does it do? Can I emulate its effect on a subtractive (or other) synthesizer?

  • 'Harmonic' isn't a common name for a synthesizer control, and even knowing what 'harmonics' are doesn't make it obvious exactly what this control does. Is this an instrument that comes with garageband?
    – topo morto
    Dec 27 '17 at 20:00
  • @topomorto yes, this instrument comes with GarageBand. Your concern is exactly why I'm wondering what it does. There doesn't appear to be a tooltip or anything that tells me.
    – intcreator
    Dec 27 '17 at 23:00

A harmonic is a pitch that is an integer multiple of the fundamental frequency. In other terms: on an acoustic string instrument, when you play a note, say 110 Hz, the string would resonate mostly at 110 Hz, but it would also have simultaneous resonances at approximately 220, 330, 440Hz and so on, that get progressively weaker. Those simultaneous resonances are harmonics. Here is a graph that somewhat explains it, the x axis is Hz, the y axis amplitude (volume) Now on your softsynth, there are three things that knob could do:

  1. Amplify all harmonics, or some of them. This would make the sound brighter, to put it simply.
  2. Change which harmonics are accentuated. This would change the character of the sound, hard to be any more specific.
    1. Change the pitches of the harmonics. This is unlikely. It would certainly allow for some weird sounds.

I suggest playing with your knob, see what happens to the sound. If necessary, use a spectrometer to figure it out. Or if there is a manual of the thing, maybe that could help.


Don't worry too much about the labels on this sort of instrument. The knobs do what your ear tells you they do. I think we can assume 'Harmonic' boosts high frequencies, 'Depth' low ones. Am I right? They aren't standard terms from classic subtractive synthesis, where you basically have a choice of waveforms, a filter and ADSR envelopes to play with.

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