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I've been trying to mimic a high-treble instrument I heard in a song where it basically goes between octaves in a wavy, smooth pattern. To do this on a piano you hit the note F3 then F4 repeatedly. But I want to make it automated and much more smoothly in Ableton Live.

Do you get the effect I'm going for or is a soundclip needed? I can produce one and post it to vocaroo or someplace.

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2 Answers

The generic term for this is vibrato, though it wouldn't usually move 'between octaves' but rather in smaller increments like semitones.

Applying a low-frequency oscillator to the pitch pin on a tone oscillator would achieve the effect. The amplitude of the LFO would control the degree of pitch shift over time, and its frequency would affect how rapidly it shifts.

In Ableton Live, you can do this using the LFOs on any of the Ableton synthesizers or on the Simpler instrument (if you're working with samples).

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If OP compares it to piano (where this is actually referred to as a kind of tremolo) then vibrato is certainly not the right way to go about this. Vibrato / LFO-FM over a whole octave sounds extremely weird and disruptive and you loose all tonal definition (unless you use a square-wave LFO, in which case there is again no smoothness). –  leftaroundabout Dec 11 '13 at 7:01
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I you want this to alternate pitch over a whole octave, but can't have the glide over all notes in between, then this is actually not vibrato but tremolo. The obvious way to achieve it is to set up two oscillators (possibly two entire synths) and modulate both in amplitude, with exactly opposite phase. You might for instance achieve this by having two instances of your synth in two tracks, one tuned an octave up, panned hard-left/hard-right, both routed to the same group channel with an auto-pan (auto-balance, actually) effect to achieve the antiphasal modulation, and then both channel mixed by removing the stereo width. In better synths, you patch together an equivalent simply with two oscillators.

That's still not very efficient! For a rather more sophisticated solution, you can, instead of "explicitly" generating the octaves, use the fact that in a normal synth the octaves are already present anyway, as harmonics. So all you really need to do is modulate the ratio of their amplitudes. This could in principle be done with a modulated EQ, but that would be even less efficient than the two-synths solution. A single comb filter will also do the trick. Doing this externally is still cumbersome because you need to track the pitch; but it turns out most digital synths actually have a comb filter built right into their oscillators! It's called a "sync" parameter. Modulating that should be the ideal solution.

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