On Mon, 29 Jan 2007 13:49:00 -0800 "ronan mcallister" <bass.woofer@xxxxxxxxx> wrote: > Sergei, Bill, > > Thank you. Tempted to take this offline since it's barely in the ALSA > realm... > > For the one prosound application, I'll not be bothered with nor will I try > to reproduce subsonic frequencies (eg nothing below 20Hz) - and for the > other application (subsonic) -- it is not real-time / "live" music so I can > tolerate a fairly long delay. > > with the RME card it appears I can realize my 5Hz -- my current quandary is > I'm not sure where to go relative to the Linux/Alsa software as I need to > have some sort of GUI and ability to implement a multi-frequency parametric > (I guess IIR based) EQ and three way crossovers. > > I'm going to start with something less controversial like a three band > parametric EQ with xovers but I hope to start off on a good foot with the > best filtering package. > > Thank you again > ronan > Well, I honestly think you shouldn't care about 5Hz except to suppress it well enough - to preserve speakers and, maybe, stomach - there is body sensitivity to infra low frequency. That is, I think you need equalization (changes in individual frequency responses) in the audible range, i.e. 20Hz and above. About IIR <-> FIR - I meant IIR for live music - at least, the higher the frequency is, the smaller delay is, but IIRs can cause unnatural sound if they are very narrow band. I.e. my idea was approximate equalization using IIR with low Q bands, like 1 bad per octave, so the delays and difference between them will be small. If you are not thinking about live music (musicians on stage), then FIR is better in a sense it by design has equal delays for all frequencies. Think about IIR vs FIR this way: *) you can't fool nature - for good frequency resolution one needs big latency or delay - the order of 1/frequency_resolution; *) FIR uses worst/"worst" case approach - it makes all delays equal, which is good for signal shape and perception - you won't have drum being heard much later than percussion because delay at low frequencies is longer, so the "worst" is not necessarily worst. On the other hand, 1Hz resolution means music from your, say, will always come with at least 1 second delay - for me it wouldn't matter; *) IIR uses as much delay as it needs in every band, so, at least, you'll quickly hear piccolos and percussion (the metal plates), but the drum/base may come too late. Regards, Sergei. -- Visit my http://appsfromscratch.berlios.de/ open source project. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
