Subject: Re: [linux-audio-dev] using SB Live (emu 10K1) for realtime sample rate conversion?
From: olaf_AT_expansions.nl
Date: Tue Aug 06 2002 - 15:54:44 EEST
----- Original Message -----
From: Martijn Sipkema <msipkema_AT_sipkema-digital.com>
To: <linux-audio-dev_AT_music.columbia.edu>
Sent: Tuesday, August 06, 2002 2:33 PM
Subject: Re: [linux-audio-dev] using SB Live (emu 10K1) for realtime sample
rate conversion?
> > Right now we're looking at the smartest way to do realtime sample rate
> > conversion (ie change playing speed) on 2 mp3 audio files at once, which
> > should be good quality (ie good anti aliasing filters), low latency
> (beneath
> > 12ms), stable, fast and the output should be send to 2 independent
> analogue
> > stereo outputs. (yes yes, *another* DJ'ing device ;)
>
> Should both streams' pitch be changed independantly?
> Perhaps there is hardware that can do this, but you can do it in software
> also.
>
yes they should be changed independently. The fact is that we want to use an
embedded PC for the hardware, so the less CPU usage we have the better,
that's why we prefer a hardware solution.
> Some hardware supports changing the DAC pitch, but most does not. Also
> most hardware probably uses the same clock for all inputs/outputs. Note
> that changing the DAC pitch this changes I/O latency since it is constant
in
> samples.
>
oops...i didnt think about that but your prolly right in that when changing
sample rates on a multi out soundcard it will change for all the outputs at
once...
> > For our proof-of-concept prototype we were looking at using a simple
> > Creative SB Live 1024 card with the emu 10K1 chipset on it. The specs of
> > this chip show us 2 independent stereo outs and on-chip sample rate
> > conversion including anti aliasing filters. Does any of you know if it's
> > possible under Linux/FreeBSD to do this? Ie use 2 stereo outputs
> > independently, and/or do sample rate conversion on the chip in steps of
> 0,1%
> > (base rate will be 44.1 KHz i think, so the sample rate should be able
to
> > increment or decrement around this 44.1KHz)
>
> I'm not familiar with this hardware, but although it may be capable of
doing
> what you
> want I doubt that is what it was designed for.
>
the Emu 10k1 was designed for this kind of things, there is an interesting
white paper on it, but i am afraid Creative implemented the chip in a
restricted way on their SB Live soundcard...
> I'd say changing the pitch in software is the better approach for this
> application.
it might be a good approach (there is plenty of source-code around that
shows how to change pitch of audio in realtime) but as said above we want to
do as much in hardware as possible to keep the CPU free for other tasks. I
guess it's a payoff between coding it in software and finding an embedded PC
board with enough juice to do pitch-changes for 2 independent audio streams
plus mp3 decoding plus all the other tasks without interruption and running
to hot, or designing our own 2 stereo out DA hardware with samplerate
convertors and anti-aliasing filters....
thanks for the feedback
Olaf
>
> --martijn
>
>
>
>
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