Quote:
Originally Posted by Michael Carnes  I've experimented with some dirty stuff (I didn't die--I'm just not at Lex) and found it to be pretty challenging. The real things that add the dirt are not always obvious and seem to rely on a somewhat 'compromised' data pathway from start to finish. |
My guess is that a lot of the dirt stems from some of the coefficient quantization issues that were described by Oppenheim & Schafer back in 1975. A fixed point filter will have noise and distortion. The 1st order filters used by the older algorithms tend to be cleaner than 2nd order filters, but a little bit of noise, times a few hundred passes through a delay feedback loop, can result in a lot of noise.
A possibility: This noise would definitely be different between output channels. I know that adding some bandpass filtered noise to the output channels, with decorrelated noise sources for each channel, can create a wider stereo image if used subtly. Maybe this coefficient quantization noise adds "depth" to the hardware reverbs. Or maybe not. Just thinking as I type here.
Quote:
|
Floating point just doesn't lend itself to that sort of stuff. Don't get me wrong--you can add schmutz, but it doesn't sound the same. I'm probably not going to spend any more time on that experiment for quite some time.
|
Program everything in fixed point MMX or SSE, and you could probably get the schmutz back. You would need to do a lot of bitwise operations to get the wordlengths and saturation headroom correctly. I've thought about doing this, then thought "nah."
I've programmed things on a fixed point DSP that is fairly close to the fixed point Lexicon hardware (the Spin Semiconductor FV-1), and I don't hear any particular "magic" versus the floating point that makes moving over to fixed point worthwhile. Maybe I need to listen to this with fresh ears.