>The output from this contains a single sample -32768 spike about a third of
>the way in for no apparent reason.


steve, your orchestra produces a perfectly clean sine sweep for me too
(winsound 3.53; gabriel maldonado's directcsound 2.70, based on csound 3.52
i think). so check your version of csound.

anyway, i don't think it's the best to put:

ilevl = ampdb(96 + p4)

according to the manual, ampdb returns a raw value of 32000 for 90dB, thus
if you take 0dB as your maximum output, a value of 90 would give almost 0dB
for 16 bits (-0.3 in fact) and not -6 dB as you seem to want.

by the way, looking at the output, ampdb doesn't seem to be extremely
precise. or is it?