Re: Patched foo_input_sacd version for high-quality DSD->PCM (88.2/96 k
Reply #31 – 2024-02-09 21:56:31
Nothing is that simple. All digital filters have a tradeoff between steepness of cutoff and "steepness of time". If you insist on a very steep cutoff you'll smear the signal in time (preringing, etc.) If you insist in a perfect impulse response (i.e. total time alignment) you'll have a shallower frequency response cutoff. So pick your poison. Thank goodness that most of the filtering necessary in sigma delta conversions (loosely all but upsampling from 44.1 or 48k) have room for a more relaxed cutoff and you have more freedom of choice. Perhaps swamping all of the above you just have to be careful with your math. No particular selection of double vs single precision floating point or any fixed number of fixed point bits is a panacea. The worst thing to do is to make some assumption like "if I always use double precision floating point I'll never loose info...", that's the mindset that leads to the most errors. All of that said, the filtering needed to go from 1 bit DSD to 24 bit PCM can be done well with careful single precision floating point or more easily with double precision. But personally I'd choose careful fixed point: the math to prove numerical accuracy is much simpler for fixed point filters. You'll have to judge the sound differences (if any) for yourself. Personally I write all of my own upsampling and downsampling and have a preference for IIR filters but they have their own math problems Adobe Audition 3.0's lowpass scientific filter set for a > 6th order Bessel response with a corner at 50k to 80k is reasonable for an offline conversion of 1 bit DSD to 2.8224MHz PCM. Then you can use your favorite sample rate converter (including Audition's) to finish the job. In a pinch I've gotten fine results doing just that tho I'm pretty sure no-one does it that way. No particular spec is useful for comparing DSP algos: Unless you do it yourself you're at the mercy of the skill of the coder of your DSP... Thanks for your valuable post - even after almost 11 years... - It took me a while to get interested in the subject again because I finally have speakers that reward me with custom resampling.