Wavetable scanning in LGPT


So I’ve been spending some quality time with LGPT lately. I like it a lot. There are some definite weak points (no prelisten, filter/pitch oscillation is .. Not great), but I’m warming up to it.
I noticed that herr prof, over at chipmusic.org, uploaded a bunch of wavetables for LGPT last year. Good stuff 👍. I was expecting single-cycle waveforms, but they are actually things like the wavetables from Animoog. They were designed to be scanned through, so you can have a dynamic wavetable synthesizer, instead of a static sound.

It turns out that you can move through a wavetable, in LGPT, using the LPOF command. Pretty cool!

A few caveats I’ve found: with wavetable synthesis, reducing noise is a common concern. LGPT has only linear interpolation, so higher frequencies will be hard to make sound good, without a lot of oversampling. So you may have to work with long files. 256 cycles, at 2048 samples per cycle, at 44.1kHz is ~11.89 seconds long! That’s a big wav file.

Also, the fastest rate at which you can update the wavetable position is on every “tick” [read here if you don’t know what that is]. So it helps if you turn up the tempo, and use more ticks per step. If you’re ok with having a “steppy” sound, then you don’t have to.

And, of course, you must increment the loop position by a multiple of the cycle size, otherwise you will be looping from the middle of a cycle, instead of the beginning. So if your cycle size is 2048 samples long [0x800 in hex], you would stick:

00 LPOF 0800
01 HOP 0000

…in your instrument table. That will move through one cycle per tick. Change it to LPOF 1000 [4096 samples in decimal], and it will progress at two cycles per tick.

Still trying to get backwards motion working right.

Just make sure you know how long the cycles are in each wav file, and you’re good to go!

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