Subject: Re: [linux-audio-dev] protux, stereo and interleaving
From: Richard Dobson (rwd_AT_cableinet.co.uk)
Date: Fri Feb 09 2001 - 21:15:54 EET
Paul Davis wrote:
>
> >Fair enough - what file format do they use though? It is a public one?
> >How do you stream/play the thing, if you have to get through 40mins of
> >channel one, to get to the start of channel 2? Can you do it with
> >'ordinary' disks? This is the big argument, about streaming formats v
> >archive formats. For example, WAVE is streaming, SDIF is archive.
>
> i would have thought that the general context of LAD over the last
> year would have answered most of these questions :)
Pity that I haven't been on the list that long! :-(.
> the files are 1 per-channel, just like protools and samplitude.
yes, a lot of programs do this (even CEP); is this out of choice, or
because of the assumption that WAVE/AIFF can't support multi-channel
data? CEP will read a m/c file, but can only write it as multiple mono.
So it is impossible to play the composite result outside the
application. This is what interests me - while I can readily appreciate
the 'editorial' advantages of separate mono files, to be able to render
the final piece independently of the application, a 'standard'
interleaved format also needs to be supported, for both reading and
writing.
>
> the file format is raw: float data, normalized to [-1.0 ... 1.0]. i
> may consider adding a WAVE header at some point, though very few
> programs will handle WAVE floating point files, so its not clear that
> there is a lot of point in doing this.
Well, there is quite a lot of point for users of WIN2k and Win98SE, as
WAVE-EX has a floating-point equivalent to WAVE Type-3, and AIFF now has
AIFF-C FL32 (now supported by Cubase 5 )and if you stream that format to
the card, Windows will render it even if the card is only 16 or 24bit.
I am half-way through making a play program for Linux that will support
WAVE Type-3 and WAVE-EX (still have no m/c card for Linux though!), and
once that is proven, the code can be added to sox, Snack, etc.
Maybe the forthcoming AES 31 standard for portable audio file exchange
(in which EDLs figure prominently) will be useful as a baseline; they
are inclining towards Broadcast WAVE at the moment; I don't know yet how
they are approaching multi-channel. The result of all this
committee-work will be a file format enabling complete transfer of audio
projects (EDLs included, and including a spec for the disk format,
probably FAT32) between applications, and across platforms. If nobody on
this list is a member of AES, it would be well worth someone such as
yourself joining. Not as cheap as CMJ, but more than twice the number of
Journals per year. Even if you end up with a Linux/Ardour-only file
format and structure, supporting AES-31 in the fullness of time might be
a good stategic move. And I can expand my multi-channel toolkit to help
glue all those mono files together again!
Richard Dobson
-- Test your DAW with my Soundcard Attrition Page! http://www.bath.ac.uk/~masrwd (LU: 3rd July 2000) CDP: http://www.bath.ac.uk/~masjpf/CDP/CDP.htm (LU: 23rd February 2000)
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