Jim Moritz wrote:

The curious thing is that if clipping occurs before the signal reaches
the sound card, the results are better than if clipping occurs in the
sound card - I would expect the effect of clipping would be similar
wherever it occurred between the IF filter and software FFT algorithm,
but apparently not so.

Hmm... This is surprising, interesting and confusing... Could it be a strange
kind of ADC or some DSP stuff on that soundcard that "wraps around"
instead of clip at 0x7FFF and 0x8000? I was playing with an ADSP2181
DSP a few years ago and I before I got the filter coefficients scaled
properly, I had problems with overflow in FIR filters. The "summing point"
overflowed resulting in a _horrible_ sound. Fortunately I found a bit called
something like "enable saturation" which made the MAC accumulator
clip instead of wrap around.

73
Johan SM6LKM