Ok, so first lets dig into the tutorial patch.
basically, it create a noise burst, controlled by a VCA, which writes into the delay buffer, and also out to the output.
the feedback loop is where it gets interesting...
working 'backwards' we can see it reads the delay line (using linear interpolation), and thats mixed in, sent to the output, and written back into the buffer. (hence the feedback loop)
at the start of this chain, we can see that delay/mtod is used to calculate the length of the delay line used (its a % of the buffer size, determined in the write object)... and then uses linear interpolation to go from k-rate to audio rate.
ok, this basically makes sense... but the bits I'm still investigating are:
- the mtod tuning reference... my assumption is this has to be configured so that it matches the delay buffer specified in delay write BECAUSE the delay time is a function of frequency but the input for delay read is a % (actually a ratio, but equiv for discussion purposes) of the buffer. BUT in practice if I tune this with a tuner, I don't see the numbers I expect.
- maths/-c not sure what this is for, it could be an offset to allow for feedback sample, but its unclear, and seems to make little difference in practice when i tested with a tuner.
- conv/interp is this required? I think this is only required if the pitch changes over time e.g. a pitch bend? otherwise pitch is constant, so no interp required. or perhaps its just 'tidier' to do this when going from k-rate to s-rate.
the main area of investigation is my understanding of MtoD and the tuning reference and how it relates to the buffer size in write... and ensuring that the resulting output is correctly tuned
(a bit concerning there is a comment that there is a bug in the tuning reference... hopefully if I figure this out, then I can 'fix it' )