[linux-audio-user] Re: Resampling Audio Libraries & Sinc

i happened to have a short glimpse on your posting, david. i don't want to insult anyone, but there is a bit more to evaluating accuracy than comparing sample values at fixed locations ;--))))))) consider a few of these things : a) non-causal algorithms introduce a natural delay. for windowed sync interpolators this is half of the filter kernel. ok, the algorithm could skip those samples of course (that's what fscape is doing by the way, if i remember correct). b) the algorithm could introduce a gain factor different from 1.0, this is in fact very likely, consider resampling 44.1 khz to 22.05 khz, a 0 dB headroom file would be distorted if there is no gain compensation. c) the crucial point about windowed sync is that it's naturally also a lowpass filter (for upsampling which you were doing in your example). so, those filters are windowed sync filters, they are linear phase and show an effect called gibbs effect which means "edges" show pre and post ringing phenomena. this is not necessarily "bad" and with not extremely long kernels it's not audible, too. in fact, when you run a software synthesizer you will most likely want band limited oscillators, i.e. those with gibbs effect. now, no realizable filter is infinitely steep, so you'll have a passband etc. summa summarum it's very likely that for an arbitrary input sound, resampling with an integer factor will *not* produce equal sample values with the factor spacing in the output. without blowing up this stupid discussion, i suggest to do two things : a) *listen* to the results for an aural comparison. this is in fact the most important point, because for different ears different algorithms are better or worse. i, for example, use bandlimited resampling in most cases and in real resamping cases (e.g. 48 kHz -> 44.1 kHz), but sometimes i prefer the additional colouring and brightening (= distortion) of say cubic interpolations or even linear interpolations which produce the hardware-sampler-kind-of-timbre. b) read a book about audio analysis, and perform some more appropriate tests, for example calculate the harmonic distortion (try your example with a sine tone!). best, -sciss- ___________________________________________________________ Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos - Hier anmelden: http://mail.yahoo.de