[linux-audio-dev] Amount of analog channels with nonuncompressing demux on ENVY24HT-S based cards

Hans Davidson harley42 at passagen.se
Fri Mar 18 01:45:47 UTC 2005

Hello !

I want to setup a multichannel audio environment for use
together with software that synthesize the waveforms for
each channel.

My newest audio card is a "Hollywood at home 7.1" card based on the
ENVY24HT-S chip.

I have managed to use the card to output mono and/or stereo sound
under Slackware 10.1, but still want to find out if the card
supports the conversion of uncompressed multichannel audio (for
example 6 or 8 16-bit (or 24-bit) samples per frame from a FIFO
through operating system and hardware) into analog signals ?

If this is not possible with the internal DACs of the card, then
I hope that it at least will be possible through ALSA with external
DACs connected to the card's optical output, that seems to be of
a high speed kind and expected to support ADAT (a standard
established by Alesis, I think).

I am not so interested in encoding the audio in DTS or some
Dolby Multichannel format or simmilar, since i want the channels
to be handled independently. For example I do not want to label a speaker
as "left" or "right" and then select the speaker by assosiating a direction
to the sound. Instead I want to be able to assign D/A channels to MIDI file
tracks or MIDI channels and then placing the speakers there I want them
(not there any multichannel decoder expect them to be).

If I try to use several cards, then a lot of synchronization
problems need to be solved, to avoid divergation in FIFO usage
between cards and to maintain phase coherency. In addition to
arrangements, like pathing cards to use a common chrystal
oscilator and/or reserving some DAC-channels for synchronizaion
purposes, I also need to convince the motherboard to accept several
sound cards without causing problems during resource allocation
(for example around IRQ mapping) or distributing the cards between
several PCs connected together with maybe 100Mbps network cards.

When I have solved these questions, then I may have to think more
about the best algorithms to synthesize sound, by looking at
existing open source programs and/or implementing additive synthesis
with or without the use of FFT or some other optimized code.

I am new to this list, so please excuse me if the answers to my
questions are hidden in any recent messages in the archive.

Thanks in advance for feedback/answers !
Hans Davidson

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