posted 30 October 2000 01:40            

bowedkarplus-strong.kym

I got a really good Karplus-Strong bowed sound using a MemoryWriter for feedback. A couple of questions arise...

1. I notice that the tuning is dependent on the LPF cutoff frequency. By setting its cutoff to 12 times the KeyPitch I can get it pretty well in tune across the keyboard. Why is this? And how do I keep it in tune with different amounts of spectral feedback?

2. I want to allow some polyphony, but when I put a MidiVoice at the right of all of it, the system complains that the MemoryWriter's wavetable is being written more than once. Since the name of the wavetable for the MemoryWriter is decided at compile time, how do I write its name so that multiple voices can allocate independent wavetables?

Cheers,

posted 01 November 2000 10:52            

That little script did the trick and I understand now how it works! I was able to get 4 voices out of it before running out of realtime. It looks like something funny going on in the last DSP, because all the others are loaded only to about 40%.

The portamento you mentioned also puzzled me but I took care of it by delaying the trigger of the bowing noise source. It looked to me like the delay line had to take at least a full-length delay cycle in order to adjust its scaling.

The filter tuning still puzzles me, but I found that by dropping the filter order to 2 I could use a darker cutoff of 9x instead of the 12x needed by a 4th order filter. No doubt it has something to do with phase shift through the filter, because in order to tune a real waveguide instrument you need to insert a fractional cycle delay using an all-pass filter. I didn't have to do that here since Kyma allows interpolation in the delay scale, and the LPF must be adding its own two cents...

Thanks again!