Ogg and 6channel playback?

[piscator]

I just encoded my first 6-channel ogg-file from an ac3 5.1 source. Now, I would like to playback this file on 6 channels but it only plays back at two channels (vorbis decoders shows it is a 6-channel file too).

I'm using a SBLive! soundcard and it's digital output. So, my guess is that it won't work with digital outputs or am I doing wrong something else?

thanks,
Piscator

[tiki4]

Please, search the forum. That has been answered rather often. Mostly that's Creative driver related problem which may be solved by downloading ChannelDownmixer DirectShow filter form www.trombettworks.com (http://www.trombettworks.com).

tiki4

[piscator]

Thanks for your fast response tiki4. I'll try it immediately. btw, I searched the forum and the ogg faqs and couldn't find the right solutions.

greetz,
Piscator

[Emp3r0r]

Your right, it won't work with digital output. the only widely supported digital audio connections are AC3 and DTS... possibly AAC in the future. In order to play 6 channel oggs you must run 6 cables (see exception to rule at bottom)!

For example if I want to play 6ch ogg through my receiver, I must run 6 cables to the 6ch ext. input and set the soundcard to 6 channel output. If I want to play 6ch AC3 I must run one cable to my receiver and set the soundcard to SPDIF.

6ch ogg to receiver with one cable is only possible with nForce AC3 encoder (which BTW adds additional encoding and decoding)!

[piscator]

Unfortunately a big concrete ceiling refrains me from running 6 cables to my ac3 receiver. And besides, I've more than plenty of cables running around already.

So for the moment, I just stick with ac3 muxing in my divx movies instead of ogg. I just hoped for a multichannel codec to downsize the ac3 tracks a bit to favor video quality.

@tiki, I didn't want to downchannel, I wanted to hear all the channels!

greetz,
Piscator

[ChristianHJW]

You may talk to the hypercube author about a real time 6 ch to AC3 encoder, so you can feed the 5.1 Ogg decoder output to the real-time AC3 encoder and pass the AC3 via SPDIF to your receiver at max bitrate .....

[tiki4]

@piscator:

Sorry, I think I got you wrong in the first place. However, there is an issue with Creative drivers and 6ch Ogg Vorbis. The channel order is somehow exchanged and you won't hear all channels on all Creative 5.1 soundcards (I've got an Audigy and I'm affected). Channeldownmixer can solve that problem by reordering (?) the channels so that all of them land at the right speakers. What you can think of course is that I use analog out with six cables. I didn't know about digital out (does that require SP/DIF? Then I understand that it doesn't work).

So, sorry, my post wasn't meant rude, but there is a very well known issue with Creative drivers and multichannel formats...

Regards,

tiki4

[piscator]

When I look at the amount of time it requires to transcode ac3 to ogg or mp3, it looks like such a real-time encoder would take quite some processing power. But it would be nice if something like that would be around.

Piscator

[piscator]

@tiki. No offense taken. I didn't have any problems with the creative drivers so far. Until I downloaded the newest drivers yesterday. From that point on, 6ch ogg wouldn't play on 2ch output. Solution: old drivers. And indeed, I use SPDIF with digital ac3 output. 6 cables is a bit too much for me and the big concrete ceiling :-)

Piscator

[ChristianHJW]

Originally posted by piscator When I look at the amount of time it requires to transcode ac3 to ogg or mp3, it looks like such a real-time encoder would take quite some processing power. But it would be nice if something like that would be around. Piscator

Not necessarily true. In the encoding process a lot of time is used to decide how much bits to spend on each sample, depending on the PSY model, such that human ears doesnt notice there is information being left out.

A real-time AC3 transcoder, as the resulting file size has no meaning at all, could use max. allowed AC3 bitrate ( 640 kbps AFAIK ) and use a very simple PSY model requiring minimal CPU time, and still the result should sound much better than the original, being an OGG at 240 kbps or an AAC at the very same bitrate. Just imagine how excellent a 448 kbps AC3 is sounding, and then consider the sound capabilities of a 640 kbps AC3 .... you dont have to invest much CPU time to make decisions on where to spend more or less bits if you have such a big bitrate available.

BTW, AC3 may seem to be CBR to us, but i heard in fact it is not. So, there shoud be a PSY model used in the AC3 encoding process for sure, and we can skip this process almost completely for a real time transcoder ....

[CaptainCarrot]

still the result should sound much better than the original, being an OGG at 240 kbps or an AAC at the very same bitrate.
I'm just curious... how would you want to create an ac3-file that sounds better than the input 6channel-file, wether it's vorbis or anything else? magic? I'd say loosing almost no quality would be the most I'd ever expect from any transcoding. Your suggestion would basically be the same as take a 500kbps divx-file and do a realtime mpg2-conversion during playback with 10Mbit to get increased quality!?!

[ChristianHJW]

Sorry, incorrect expressions. Of course the AC3 cant sound better, what i wanted to say is that normally an 640 kbps AC3 ( when made from the master ) should sound so much better than a 6ch Ogg or AAC at 1/3 the bitrate that there is not much loss to be feared when transcoding ...