Subject: Re: [linux-audio-dev] using SB Live (emu 10K1) for realtime sample rate conversion?
From: olaf_AT_expansions.nl
Date: Wed Aug 07 2002 - 11:01:39 EEST
----- Original Message -----
From: Frank van de Pol <fvdpol_AT_home.nl>
To: <linux-audio-dev_AT_music.columbia.edu>
Sent: Tuesday, August 06, 2002 11:36 PM
Subject: Re: [linux-audio-dev] using SB Live (emu 10K1) for realtime sample
rate conversion?
>
>
> On Tue, Aug 06, 2002 at 02:54:44PM +0200, olaf_AT_expansions.nl wrote:
> >
> > 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.
>
> Hi Olaf,
>
> most (if not all) soundcards that feature downloadable wavetable synths
> feature a number of phase accumulators to perform the sample rate
> conversion. As a bonus these voices typically also provide (resonant)
> filters :-). Routing individual voices to different busses (to get your 4
> distinct outputs) could be an interesting challenge. On the other hand the
> emu10k driver supports reverb/chorus 'effect sends' per voice, so it can
> address at least 4 busses (mix L/R + eff 1/2).
>
> The voice should be set to loop; while your program replaces the
> to-be-player portion of the buffer with the appropriate fresh data.
>
> An example of the implementation of wavetable support can be found in the
> alsa synth subsystem (in alsa-kernel). The Gravis Ultrasound Classic
driver
> could serve as an example where the synth is used to playback a pcm
stream.
> I know code exists to play audio files through the emu8k synth but have no
> experience with it
(http://www.maz-sound.com/archives/awewaveplayer-03f.tgz)
>
>
> Of course all this hassle makes your mp3 box very hardware dependend and
not
> very portable. If CPU power is no objection I would opt for the software
> solution (which could give you also the possibility to scrub/play the
sample
> backward like on a normal deck (turntable). (see alsaplayer /
terminatorx).
>
unfortunately CPU power is a problem, so it doesn't seem an option to do
high quality sample rate conversion and anti-aliasing in software as our CPU
will probably run out of juice... btw, there is also hardware that can do
the scrub thing these days, my idea was as most DAC's (like the Crystal DA
converters) offer sample rates from 2kHz up to 100kHz by setting the
masterclock freq this could also be done using a hardware solution...
wat i don't understand right now: f.e. the EMU 10K1 chip also offers custom
sample rates by setting a master clock, but non of the drivers i've seen
seems to have implemented this...i think this is because of the fact that
the Creative hardware on which the emu chip is used doesn't cater for
non-regular sample-rates?
thanks for all the feedback!
Olaf
> Cheers,
> Frank
>
>
>
> --
> +---- --- -- - - - -
> | Frank van de Pol -o) A-L-S-A
> | FvdPol_AT_home.nl /\\ Sounds good!
> | http://www.alsa-project.org _\_v
> | Linux - Why use Windows if we have doors available?
>
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