On Mon, 2007-01-15 at 11:12 -0700, Bearcat M. Sandor wrote: > On Monday 15 January 2007 08:54 in an email titled "Re: > Multi-channel audio with a computer front end" Paul Davis wrote: > >in other words, i'm totally confused by your goals. > > > >--p > Thanx Paul. Here is what i am trying to do. I want to use my computer as a > front end in a multi-channel system with a little as possible between it and > the amplifiers for purities sake. I do not want D/A conversion inside the PC > as that is noisy and jittery. I do not want to use spdif or toslink as those > are also jittery (or so i understand). > > The Slim Devices (squeezebox or Transporter) are fine for stereo but will not > work for multichannel due to latency issues. You can send a digital signal to > a pre/pro from them but that adds a pre/pro in the mix and i'd rather not. > > So that leaves me with usb or firewire. you still seem very confused. or i am. or both. first of all, D/A conversion associated with the computer does need to be noisy - there are many devices with external breakout boxes now - and it does not need to be jittery if you are willing to spend money on good equipment. i would agree that doing it inside the chassis case is probably not the best arrangement, but thats not much of an issue these days. secondly, s/pdif is not inherently jittery - jitter is determined by the sample clock, and that can be extremely low jitter or extremely high jitter depending on where it is coming from (i.e. who makes it). toslink is not an alternate protocol, its a physical connector+cable. you can use toslink to transmit S/PDIF or ADAT or a few other things as well. > Can my system send all the channels to one of these devices via usb or > firewire and have the device break them out and send them to the appropriate > speakers. for example, i run an RME digiface, which has 26 channels in and out. the i/o box is external to the computer, connected by a 4m firewire cable (though it doesn't use any standard firewire protocol). the digiface is digital i/o only, so i then route its i/o to and from a couple of 8 channel frontier design Tango24 converters which are in turn connected via a patchbay to the analog part of my setup. the RME multiface is an alternate breakout box that has D/A converters built in for 8 channels. RME solutions have too high a channel count for you, however. > These devices know nothing about DTS, DD and the like so the > computer would have to determine what sound goes into what channel and send > all that to the device. I know that were i using a mixing like Audacity or > Audour it could be done, but the question is can the media player engines > (gstreamer or xine) do that as well? if they can emit ac3 encoded audio, it be sent passthru over any s/pdif connector. if they can't, then you're stuck with a multi-channel signal stream. > If that answer is "no", then i can move the attention down to stereo USB > devices. Since linux can use multiple sound cards i could purchase 3 stereo > USB devices. Could I have Xine or Gstreamer send the front channels to one, > the centers to another and the l/r rears to another? If so, am i going to > run into a problem with timing issues between the 3 devices? Is USB going to > cause such latency problems? any configuration involving more than 1 digital audio device *must* include a shared sample clock source in order to avoid sync issues. no exceptions. > then i am limited to what the pre/pro understands and i want to play with > things like ambiophonics and such. I'd also like to do a little mixing and > recording and a pre/pro isn't meant for that. pre-amps in the pro-audio sense have no role to play here. by the time the signal leaves a D/A, its already line level. unless you mean "preamp" in the home stereo sense, which is basically just a volume control, source select and optionally tone controls. i can see no role for a transporter in anything you've described. what you need is a PCI audio interface with multiple channels and an external breakout box. if the interface only does digital i/o, then you need an additional external multichannel D/A box as well. the transport is a device to use network protocols, either over a physical ethernet or wifi layer, to move audio data from the computer disk to the D/A's built into the transporter, or to be resent using s/pdif via its digital outs. it is a two channel device, and so plays not role in a multichannel set up. --p
