MP3 over S/PDIF via Dolby Digital not PCM

[RAzOR]

I can play MP3s over my S/PDIF but I am pretty sure it is in PCM. When I play DVD formats, the audio goes Dolby Digital.

The problem is with PCM that the volume settings on the laptop (playback device) affects the volume of the PCM signal to the decoder. With Dolby Digital it has no effect. This is what I want. The player to simply be a source and nothing else.

So what I really need is a real time CODEC that takes MP3 and/or PCM stream and converts it to Dolby Digital in real time then out the S/PDIF.

Any ideas? I use the VLC open source media play on XP.

[andy]

You don't want to do that beacuse you will be taking one lossy format (MP3) and then recompressing it into another lossy format (DD). Just leave the volume on your computer at maximum.

[RAzOR]

That makes sense but I was under the impressions that once a file is digital, digital to digital conversions are lossless.

I have been doing more digging and I think I need an AC3 CODEC that has more bells and whistles.

[andy]

That's not true when you convert between lossy compression formats like MP3, and Dolby Digital. Each time you convert from one to the other you lose some quality.

If you want to encode DD in real time, you need something called Dolby Digital Live. This will require a new sound card. It might not solve your volume problem though. The reason you can't control the volume when outputting DD is because your sound card simply passes along the DD stream exactly as it comes off the DVD. It can't adjust the volume because it doesn't understand the data. A sound card that's encoding its own DD signal will probably be able to adjust the volume of it.

[RAzOR]

Aren't they only lossy when compressing? I thought conversions were lossless. And thanks, I thought you might recommend DD Live. I will have to consider potential losses should I try this out.

[andy]

Aren't they only lossy when compressing? I thought conversions were lossless. And thanks, I thought you might recommend DD Live. I will have to consider potential losses should I try this out.

The problem is that in order to convert it from MP3 to DD it has to decompress it to PCM, then recompress it as DD. There's no way to do a lossless conversion. You may not be able to hear any difference, but it's not the best way to go if you can avoid it. The only reason to use DD live is if you want to send surround sound to a DD decoder.

[whoaru99]

Have you tried using kernal streaming or ASIO drivers? These, I think, bypass the (assume) Windows mixer.

[RAzOR]

The problem is that in order to convert it from MP3 to DD it has to decompress it to PCM, then recompress it as DD. There's no way to do a lossless conversion. You may not be able to hear any difference, but it's not the best way to go if you can avoid it. The only reason to use DD live is if you want to send surround sound to a DD decoder.

Ahhh, so yes, double loss. Did not know they didn't directly convert. I will try to avoid that for sure then.

[RAzOR]

Have you tried using kernal streaming or ASIO drivers? These, I think, bypass the (assume) Windows mixer.

No, I have not. What are those exactly? Protocols?