[dale116dot7]

Originally Posted by Casey

What are you modulating?

I've done a bit on various portions - taps, allpasses, loop size. But if I turn modulation off, I don't get nearly as smooth of a response as, say, any of the algorithms on my PCM91 with their chorus functions also turned off. I check for chorus being turned off by watching for modulation with a tone. Sometimes strange things will cause chorus enabling like using spread and shape in the random hall algorithm.

I can modulate up to eight taps at once. I have not set up a queue structure, though, to allow modulation or glides of more than eight taps 'in turn' - where eight things modulate simultaneously, then you sub out something that is modulating with another tap that is frozen - rotating the modulations. I could do that, I just haven't written the code to do that because I thought that eight modulating taps should be enough.

Are any taps in the feedback portion of an allpass?

I've done it both ways. With high allpass gains (any higher than about 0.6) the signal in the feedback portion appears a bit odd. But at allpass gains less than about 0.4, the audio in the feedback portion of a lattice allpass appears pretty useable - it doesn't really sound odd to me.

Or are you first getting your basic loops set up with out allpasses?

Yes, and I do find that the combing comes and goes with or without allpasses. It has to be created by interference between tap locations. At high gains, the allpasses have a 'grainy' or 'ringy' sound to them with impulses. It doesn't sound allpass but it measures that way. You can hear them get 'excited'. With real audio, that mostly goes away. But if I run the same test with the PCM91, there is still a repeating pattern, but the grain goes away and that makes the excited frequencies not sound so much. It does even without chorus turned on. Should I be changing the feedback gains on the allpasses based on the allpass length or size?

Would a valid way of figuring out reasonable allpass gains would be to change the allpass into a comb by imbalancing the feedback and feedforward terms, then adjust the gains to flatten the frequency response of the combined combs? I have a feeling that if I can manage to get a flatter allpass response, I should have a better sounding algorithm. Or perhaps feed an impulse in it and do an FFT of the result and adjust the gains to flatten it?

It is certainly possible to have a single set of taps with constant ratios that are scaled with size, or used with any number of RT values.

I would have guessed that it should be done that way - the RT should change the recirculation gains, and size should be able to just resize the array linearly. But I've been struggling a bit to get it all to work - not from a technical perspective because that is just plain coding - but from an sound point of view - something that sounds good.

For reference, I set up the 'infamous' Dattorro/Lexicon algorithm, and that algorithm does sound pretty good using the same building blocks as what I am using for the newer algorithms. I did that just as a sanity check to make sure that the base building-block algorithms are doing what I expect them to do. It sounds similar to (though not exactly like) a PCM91 'Room' setting.

-Dale