Re: [LAU] surround sound with stereo usb DACs?

From: nescivi <nescivi@email-addr-hidden>
Date: Sun Jan 11 2009 - 07:52:10 EET

Hiho,

On Saturday 10 January 2009 02:16:04 Justin Smith wrote:
> On Fri, Jan 9, 2009 at 10:59 PM, Bearcat M. ªandor
> <HomeTheater@email-addr-hidden-soul.com> wrote:
> > Folks,
> >
> > I'm slowly building a hi-fi surround system around Trends Audio products.
> > They have a nice, little, stereo usb DAC. I am really only looking at
> > wanting 4 channels for now. I have something like 8 usb2 ports on this
> > computer so i have plenty.
> >
> > Can i have my player (xine or mplayer or what have you) decode the
> > signal be it dolby digital, dts, or the blu-ray formats (ha) into
> > channels and then send (right and left) out of one usb port and (right
> > rear and left rear) out of a second usb port to a pair of these stereo
> > DACs. I assume if i eventually wanted an 8 channel system i could so the
> > same thing with more channels?
> >
> > Is this feasible? Any drawbacks?
> >
> > Also, those Trends Audio TA-10.1 are awesome.
> >
> > Thanks.
> >
> I am under the impression that with multiple sound cards you have the
> issue of clock drift, the audio channels would eventually go out of
> sync, and this would get worse and worse over time. When only one
> sound card is being used, the application can sync the video playback
> to the audio device, since video speed is not as evident a distortion.
> With multiple audio devices with separate clocks, you would most
> likely get annoying phasing and comb filter artifacts, if not a
> distinct echo. There are firewire cards that can share a clock in
> order to eliminate this problem, but I have not heard of USB cards
> that share a clock pulse.

There are a couple of issues: can the audio software keep things in sync,
without having problems writing to the different devices. There clock drift
is an issue and I'm not sure how well ALSA deals with combining several
usb-audio devices.

Another question is how well the USB subsystem deals with several high traffic
streams. Are the Trend USB devices USB1 or 2? The latter would be novel,
since there aren't many audio USB2 devices out there that adhere to the USB
audio standard (and thus work on Linux). You can get this info with (possibly
as root), when the device is attached:
lsusb -v

Then depending on how you place your speakers, how good your speakers are and
which channels from which USB device you use for which speakers.
I imagine it would be a bad idea to have the front stereo pair of a dolby
surround come from two different devices. Rather separate the devices into
back and front.

If you have an acoustically perfect room and have very accurate speaker
placement, or are trying to do things like ambisonics or wave field
synthesis, then no, it's not going to work.
If you use this setup in a normal living room setup, where you have to
compromise between a free path to the kitchen door, speaker placement and the
dogs basket, then you might get acceptable (but not perfect) results using
the separate USB devices.

sincerely,
Marije
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Received on Sun Jan 11 08:15:02 2009

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