On Mon, 29 Jan 2007, Sergei Steshenko wrote: > On Mon, 29 Jan 2007 13:06:34 -0800 (PST) > Bill Unruh <unruh@xxxxxxxxxxxxxx> wrote: > > >>> I said "observe", not "hear". I am saying that to roughly estimate that >>> a signal contains a 1Hz spectral component one has to observe it (with >>> his/her eyes, or scope, supersensitive to infra low frequencies ears) for >>> at least one second. >> >> It is certainly true that a bandpass filter rings. Not sure I would call >> that a delay. If I hit a bell, is the sound that comes out a "delay" on >> the hit. I suppose you could say that. >> > > I insist on that. Take Octave/Scilab/MatLab and simulate this: > an burst (i.e. a limited number of sine wave periods) going through > an oscillating loop - the DELAY, i.e. the moment at which output > amplitude more or less reaches input one, will be abot Q periods - I'm > talking about a burst of more or less resonance frequency. > > >> But this is true always. And I assume that the reason he needs to form the >> response is to make up for deficiencies ( in the room, the speaker, >> whatever) that already have that ringing in them. And if the ringing of the >> filter is out of phase with that of say the speaker, then the two will >> cancel. >> >> I have however no idea whatsoever why he wants what he claims he wants. >> What I was responding to was his desire to replace analog circuits with >> digital Linux driven filters. I assume he already has low frequency narrow >> band filters that he wants to replace ( or maybe avoid buying). Any >> comments you make about the digital is equally true for his analog system. >> Thus IF he want those kinds of specs for his analog system, then the >> digital system will give them to him as well. It is not latency. it is the >> natural response of the system, analog or digital. Latency is the delay in >> the digital processing of signals, which is completely irrelevant at low >> frequencies. >> > > ???????????????? > > > How come latency/delay is irrelevant ? Because the digital latency is so low-- a msec at worst, which is irrelevant to low frequencies. > > Ronan is in the real of live music, so the audience will hear > both direct from the stage sound and PA one - the interference between > the two directly depends on latency/delay - nobody cares what cause > the phase shift - digital (+ FIR) latency or IIR/analog filter group delay > - the latter two are the same in their physical/mathematical nature. As I said, I assume he wants a filter board in order to compansate for problems in the chain-- speaker resonances, etc. But he has not said why he wants his ultra low frequency equaliser board. So we have no idea whether or not it is a good idea. > >> So, can he replace his analog filter board with a digital one. I would >> worry about this at high frequencies when the latency-- the time between >> reading a word from the sound card input to that byte or anything affected >> by that byte being delivered to the output of the soundcard-- becomes a >> worry. The argument that the ear cannot tell if something comes in 1/100 >> of a sec late is a reasonable one to say one should not have to worry about >> the latency. I am not sure it is right, but it could be. >> >> But latency at 10-100 Hz is completely irrelevant. > > See above about latency and interference. > >> >> (Note if you know the signal you can tell its frequency in far less than >> one cycle. If I hand you a sine wave with infinite precision you can tell >> its frequency in an arbitrarily short time.) If you have an unkown signal >> shape, then its period is both hard to define and to measure in less than a >> period. >> >> > > But sound comes with no tag attached, saying it's a 1Hz signal. And > that's why any DFT has Fsample/Number_of_samples spectral resolution. AGain that depends. If you are searching for a sine wave of undetermined period, you can determine the period far more accurately than that. I agree that the naive fourier transform will give that result. > > > Regards, > Sergei. > > -- William G. Unruh | Canadian Institute for| Tel: +1(604)822-3273 Physics&Astronomy | Advanced Research | Fax: +1(604)822-5324 UBC, Vancouver,BC | Program in Cosmology | unruh@xxxxxxxxxxxxxx Canada V6T 1Z1 | and Gravity | www.theory.physics.ubc.ca/ ------------------------------------------------------------------------- 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
