[jkeny]

I have been told that as multichannel audio (AC3 etc) is a lossy compression format it is worse quality than PCM audio.

Has anyone a measure of this degradation? Would it equate to MP3 128 kbps, 164 kbps or what level?

I am thinking of using a PC to do a digital crossover. Using BruteFir to do the crossover (and later room correction) and then using realtime AC3 encoding (using Nvidia soundstorm motherboard or soundcard). I  should then be able to route the AC3 signal to a digital receiver (like the panasonic SA-XR*) so keeping all signal digital until speakers.

This is only worth it if the AC3 lossy compression is of a suitable high quality. Any ideas

John

[ted_b]

What kind of MCH audio are you looking to use AC3 for?  Movies, games, music?  If it's movies or games, yes, AC3 is the standard (or DTS) and it's lossy compression is inferior to PCM, but to equate it to 128MP3 is probably too pessimistic.  Certainly DTS is a 400-800k type of vehicle; DD is 384-448kbps.   But if it's music you are after, why use AC3?

Ted

[JoshK]

I am thinking of using a PC to do a digital crossover. Using BruteFir to do the crossover (and later room correction) and then using realtime AC3 encoding (using Nvidia soundstorm motherboard or soundcard). I  should then be able to route the AC3 signal to a digital receiver (like the p ...

This doesn't answer your question as I don't have such measurements on hand, but in truth there is more to it than one clearly trumping the other.  My comment is related to the above substatement.  Are you aware of the required processing power you are going to need to do FIR, room EQ and encoding all on the fly?  It is going to be tremendously difficult to do without hiccups.

[jkeny]

JoshK,
My first approach is to check if this can be done and then check how realistic itis. You're right this would require a lot of processing power although I intend to use a soundstorm sondcard which will do realtime AC3 encoding in hardware. I beleive BruteFir can do Xover and room correction on less powerful PCs.

John

[dwk]

I answered on your other thread (I'm not quite sure why this needed a brand new thread), but I think you need to do a bit more learning before jumping into this.

Simply put, DD/AC3 is just a BAD idea for what you're trying to do.  The whole point of doing DSP crossovers and running them via digital out would appear to be to get a 'high quality' solution. You'd be throwing away whatever quality you were attempting to achieve and then some by compressing the audio.  Even with the somewhat degraded performance of the Panny analog inputs, you'd be WAY ahead of the game by running 4-channel analog outputs from a decent soundcard into the Panny analog inputs rather than putzing around with realtime compression.  Remember, one of the things that got the whole Panny receiver buzz going in the first place was the guy from Newform doing a digital xover using the DCX2496 running into the Panny analog inputs.
 

Furthermore, in an extension to what Josh said above, a digital xover with BruteFir is not a point-n-shoot solution. You have do to a lot of measuring and spend a lot of time in filter design etc to get decent results.  I don't want to be to negative, but given the basic level of the questions you're asking I think it will take you a fair bit of time to come up to speed to the level needed to make that work.

Given that you appear to be very new to this area, I'd suggest one of these options things to get you going:
- just get a Behringer DCX2496. With the price drop it's only $250. Tack on maybe $60 more in adapters/cables, but you have a system that will give you a shot at something that works pretty easily as these things go.
- investigate the KX-project drivers and an Audigy based card. There is a pretty decent crossover plugin that works with these drivers. There is a lot of info on diyaudio on this.  You'll end up resampling to 48kHz, but it'll still sound 'decent'.
- similar to the above, look at the xover plugin for Foobar.

If you *really* want to 'stay digital', then the ONLY currently viable option is a soundcard with multiple spdif outputs, running into multiple Panny receivers.  The Emu 1820 should get you there if you use Foobar via ASIO, and set up your PatchMix routing properly.

I'll also suggest that the Panny might not even be the best way to try to tackle this problem anymore. I have spend a fair bit of time planning a system around multiple Panny receivers running digitally, and I'm close to bailing out on it. With the various Tripath amps available for incredibly cheap prices, I think a *good* soundcard (eg Emu 1820M) (or even a DCX2496 for that matter) and some Tripath amps is a very viable approach, for about the same price as two Panny receivers.

[geofstro]

I for one am glad jkeny started these threads since I'm learning some valuable info from the responses, especially yours dwk.

I have an E-MU 1212m which is upgradeable to an 1820 and I'm thinking of employing a software XOVER solution just to separate the subwoofer from the main speakers which are single driver horns. This will be for ASIO playback of music, so I will check out the Foobar xover plug-in you mentioned. I would also like a solution for movies if anything exists on the Win XP platform. I'd be content with an analog solution, since the sound via analog out from the E-MU is so good.

Do you know of a way I could play external sources through the PC and apply the software XOVER for those in realtime as well?

Also, do you have an idea of how well a software XOVER solution compares to an electronic XOVER such as those from Marhand or even a Behringer?

Any other tips will be appreciated. Apologies of this is taking the issue slightly off topic.

geoff

[AphileEarlyAdopter]

dwk,
you can use the Tripath amps, but you still have to solve the multi-channel volume control problem.
The XR50 analog stereo inputs seem to be very transparent. You can try two of the XR50s or if you dont mind the slight degradation you can try one XR50 with DVD Multi IN.

[jkeny]

Thanks for your replies guys and all the info. Sorry about the posting on other sites - some don't respond - I didn't know if I would get a response here.

DWK - thank you for your help I take on board what you are saying - I have two sonic impacts on order but I saw a cheap panny and wondered about this all digital approach.

Why did you give up on panny? Have you seen this thread in another forum? http://www.diyaudio.com/forums/showthread.php?s=d667e6533d08c29f4c5f2f46e4fe92a8&threadid=22741&highlight=