Getting audio to a pc crossover

GestaltH

Member
2008-01-21 6:44 pm
Hi,

I have seen a lot of people that are using a dedicated pc for DSP and crossover duty. I was wondering how are people getting the audio data from their main pc to the dedicated box? I am interested in 7.1 solutions. I am also interested in relatively low latency so that it could be used for things like video games also.

SPDIF pass through seems like a good choice for music and movies, but then what about video games? They're not encoded in Dolby Digital or DTS.

Anyone have any ideas?
 
Hi,

On the "player" PC I'm using a sound card with multiple digital outputs and connecting them to multiple digital inputs on the crossover PC. Surround decoding is done on the player, so the crossover system only ever has to worry about one format of audio.

Provided you have enough I/O on your cards I don't think there are any reasons not to do things this way, and given the limitations of available software I think it simplifies things a lot.
 

GestaltH

Member
2008-01-21 6:44 pm
Thanks for the feedback.

I was thinking of something like this. The only cards that I saw that had a lot of digital I/Os were the RME and M-audio cards although I'm sure there are more. The main problem with these for me are that they are quite expensive for an audio card. Anyone know of some affordable ones?

I was wanting to do DSP room correction and crossover for a 7.1 or 7.2 system. That would mean 3x7 + 2*1 = 23 digital outputs (for 3 way speakers) on the DSP system (I want to locate the DACs on the actual speaker, so I can't use analog outs). That would necessitate at least two of the higher cost cards for just output plus one on the source system. This is way too expensive. I was thinking about trying to DIY up a simple firewire card for use in Linux that just uses I2S for all of the I/Os. I'm still researching whether this is feasible or if I should just save up my money and buy the commercial products.

Wingfeather: I would be curious to know what your setup is. Are you using DSP or just crossover? Are you using Linux or windows? What sound cards are you using, etc?
 
Hi GestaltH,

Sorry for the late reply, I totally lost track of this thread.

My player PC has a Lynx AES16 in it which is a 16-in, 16-out all-digital card. My crossover PC has a Lynx TWO-B which has a digital input and the analogue outputs for my 3-way speakers. The TWO-B functions as the clock source for the system.

Lynx cards are expensive, but if you live in the UK (as I do) then the excellent exchange rate means that buying them directly from the US gets you them for about half the UK list price (shhh!). Lynx cards are rock solid and sound fantastic - I would say they are worth the money (at the low price), if you're willing to pay it. RME are a bit cheaper in general; their AES-32 looks pretty much equivalent to the Lynx AES16, and their HDSP9632 seems about equivalent to the Lynx TWO-B. Cards from both manufacturers can be used in multiples (I think, up to four of the same type of card in one machine) if lots of channels are required.

I'm only actually using this setup for two-channel playback, as the single TWO-B I have only has 6 analogue outputs. But I do know that the AES16 works perfectly with multichannel outputs from DVD player software and suchlike 'cos I've tried it.

My crossover PC runs Windows, and I use a VST host called Bidule to run the processing itself via VST plugins. The processing is essentially just driver EQ and crossover - no room correction or anything like that.

DIYing a Firewire interface sounds like a lot of fun! I'd love to do a project like that someday, but right now I just don't have the knowledge of OSes and drivers and things.

As for locating the DACs on the actual speakers - that's a nice idea. One thing that springs to mind with it though is clocking practicalities. Everyone moans all day about the jitter made by AES/EBU and S/PDIF, and the easiest way to get rid of it is to have the DAC serve as the clock master for the digital system. This isn't possible if you have separate DACs in all the speakers. I think I would personally prefer to have a big box of DACs located centrally, all running from a single clock and providing a reference clock for the source. If you give it balanced outputs then I don't think you'll lose much by connecting to the speakers (which will still have power amplifiers in them) via cables. But that's just me :)
The other jitter-busting option is of course to have multiple PLLs with a FIFO buffer at each DAC. But I think that's a lot more effort overall and theoretically doesn't totally remove jitter.