Re: [linux-audio-dev] Linux Alsa Audio over 1394 - a Thesis

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Subject: Re: [linux-audio-dev] Linux Alsa Audio over 1394 - a Thesis
From: Martijn Sipkema (msipkema_AT_sipkema-digital.com)
Date: Wed Feb 26 2003 - 18:05:30 EET


> > Well, I'll shut up about it. I still think it is a mistake. I haven't
heard
> > any
> > convincing (to me) arguments why an application should not handle
variable
> > sized callbacks.
>
> Because it makes certain types of processing viable, which they are not
> really in variable block systems (eg. LADSPA, VST). Have a look at an
> phase vocoder implementation in LADSPA (e.g.
> http://plugin.org.uk/ladspa-swh/pitch_scale_1193.xml) or VST and see how
> nasty and inefficient they are.

If I understand that code correctly then you wait for 'FFT frame size'
samples
to be available and then process that entire FFT frame. This will not
introduce
a variable amount of processing time/sample and will not work for large FFT
frames. Adding en extra FFT frame delay and processing asynchronously
would solve this. I'm not saying this is easy, but I don't think an
algorithm
like this should rely on a callback being one (or more) FFT frame long.

> Conversly we haven't heard any convincing arguments about why we should
> have variable block sizes ;) I don't think that allowing (some?) USB
> devices to run with less latency counteracts the cost to block processing
> algorithms.

I think is at least as valid an argument as a possible increase in
performance
for some algorithms on some hardware.

> I dont know what EASI xfer is.

EASI is a hardware abstraction framework from Emagic. It was meant to
be a open alternative to ASIO. It didn't make it and now that Emagic
has been acquired by Apple it is no longer supported by Emagic I
guess, as I can not find anything about it on their site anymore.

http://www.sipkema-digital.com/~msipkema/EASI_99may25.pdf

--ms


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