ogg-audio-to-AC3-SPDIF-Filter !?

[Okraml]

Hi everybody!

is it possible to code a filter, that gets a 5 channel ogg-audio from an ogm and converts it to AC3 and send it to the SPDIF as a real AC3 Signal?
The Besweet-Develloper have an AC3-Encoder implemented, so why not such a filter??

What do you think?

:-) Okraml

[Latexxx]

Don't know about that, but downmix your audio to dolby pro logic 2 (surround2). Then encode it to 2 channel vorbis(ogg is just the file format "container"). When playing connect your pc's line-out to your home theater set and set it to dolby pro logic mode and enjoy surround audio.

[Okraml]

as i know there ist a 5.1 channel ogg-Format.
and it contains 5.1 real channels like dd5.1 does but needs less space.
There it would be nice to play it as a DD5.1 AC3 Stream to my DD Receiver.

:-) Okraml

[Defiler]

Your best bet is just to do 6-channel analog output from your PC to analog inputs on your receiver. Your PC can make better decoding decisions anyway, even though I've not run into any software that truly takes advantage of that fact.

[DSPguru]

i could write that filter, but here's the implication :
you have an AC3 source
you decode it
you encode it to 6ch vorbis
you decode it
you encode it to 5.1ch AC3
your reciever decodes it.

by than, quality should suck badly.

wouldn't it be better to directly transcode your 448kbs AC3 into 256kbps AC3 ?
on a side note, i really doubt that Vorbis is currently a good codec for multichannel audio.


Cheers :),
Dg.

[Okraml]

@DSPguru
first THX for your Answer.
Now here my thoughts about it:
1. if i devide 448/5 i get 89,6kbit per channel for a AC3
with this Bitrate OGG gets 2 Channels in a very good quality.
so with half of the Size you get the same quality like the AC3; with half Bitrate AC3 you get a poorer quality or?

When the filter then encodes back an AC3 you can encode it back as a 448kbs AC3 Stream without to much lost quality.

2. Wenn i play a Movie from DVD and let my PC decode it and send it analog to my Dolby Digital Decoder, i get poorer Quality as if i send the AC3 Stream directly to my Decoder.

3. Not every Decoder has Analog Input, but most have AC3 input (Coax or Light), so on some Decoders there would only be a Stereo or a Dolby Surround Signal from the Multichannel Vorbis-File (i think).

so if you could write that filter and its not to much work for you, please do it *g*

:-) Okraml

[DSPguru]

@Okraml
why won't you simply give it a try ?

1. take a 448kbps AC3,
transcode to 6ch vorbis,
decode to multichannel wave,
encode to 640kbps AC3
decode with your home equipment

2. take a 448kbps AC3,
transcode to 256kbps AC3
decode with your home equipment

Dg.

[Okraml]

Ok
i will try and post my results...

:-) Okraml

[Okraml]

i wanted to try, but have a problem...

first: i wanted to transcode the AC3 to a lower Bitrate like Doom9 Tutorial (http://www.doom9.org/ac3machine.htm) but in AC3Maschine 0.4 that i use, there ist no funktion to transcode to AC3. What is wrong???
But ich Decoded it with another Prog and encodet it with Sonic Sound Foundry to 224kbit AC3.

second: i transcoded the AC3 to Multichannel OGG, but how can i transcode the ogg to 6 Wav-Files (with Graphedit i could only trancode it to a 6 Channel Wav), so that i can encode another AC3???

:-) Okraml

PS: the Multichannel Ogg sounds good (but i can only hear the Stereo Channels)

[31 Flavas]

Originally posted by Okraml

Ok, i will try and post my results...
Heh, the second Star Wars EP1 was on dvd there were asian bootlegs of it with DTS. Guess what the bootlegers used as the source for the DTS track?

Please don't tell me you would want a copy of your movie (with the same kind of DTS track) because of the DTS logo....

-flavas

[ChristianHJW]

Have a look here : http://forum.doom9.org/showthread.php?s=&threadid=27718 .

In the end i am convinced we will have a nice 150 kbos Vorbis 5.1 track and we can send it to the external receiver using a 556 kbps AC3 encoded on the fly ...

[Neo Neko]

Hmmmm. Yes. Transcoding is awful when you want to lower the bitrate. But when going the other way it is not quite so bad. DVD AC3 is very good quality to begin with. Compress that to multi-channel Vorbis. Then send it back out as high bitrate AC3. There "will" be some transcoding degredation on the final step. But it should be minimal. By that time the AC3 and Vorbis codec should have discarded all the audio they are going to. So that last step up to high BR AC3 should not be a problem other than the CPU hit. If you have the time to play with it DSG give it a go. It does sound feesable. Not perfect. But workable. I think it could find alot of use.

_________________________________________________________________
A bit OT here. Does anyone know of any good lossless codecs with ACM interface? Something like Monkey's, LPAC, FLAC, etc. I would like to find something like this for my captures. :) If they don't exist could someone create if they get the time? ::)

[Emp3r0r]

well just so you guys know, i did a small test encoding to vorbis 5.1 and then playing it back using my HARDWARE AC3 encoder in my nForce southbridge... results are very promising! I'm assuming AAC works just as well if not better. Time to start playing with AAC. I have a theory that DP2 sent out AC3 will all but make getting new a new DP2 reciever pointless.

[Phanton_13]

de digital imput in the receiver not only is for ac3 or DTS, but they acept uncompresed audio, i can conect my old DAT recorder to my receiber and I haven't any problem, the problem is create a driver for it.

[spyder]

I think you will see very little quality loss if you output at the highest possible AC3 bitrate(640kbps I think). Do any recievers support raw PCM in 6 channels?

[Emp3r0r]

nope, 6ch requires compression

[Tes]

I think that having at least 6 discrete channel inputs on receivers is pretty much a standard on newer models, at least mine has them. But if you want to use the analog inputs on a receiver then a good quality soundcard is required (and it must also have 6 analog outputs).

EDIT: Oops, saw that the original question was for PCM inputs not analog. I have never heard of a receiver with 6 PCM inputs. Although a 6 channel WAV could probably be sent over a single digital connection I doubt that a receiver would know how to decode it properly.

[MaTTeR]

@Emp3r0r

I'm seriously thinking of getting the nForce for my HTPC. Can you confirm the board will pass a 5.1 AC3 properly without re-encoding or molesting it? I like the whole concept of hardware encoding on the fly but I would only use it for 2ch Vorbis or MP3 sources most likely.

Any chance the software allows you to delay certain channels? I could only wish:D Sorry to revive this old thread but you sound like the nForce expert here.

[Emp3r0r]

Can you confirm the board will pass a 5.1 AC3 properly without re-encoding or molesting it?Well, technically I can't confirm this but I can say it appears that the nforce is doing the pass-through correctly. I say this because when I play an AC3 file, my decoder's lights will flash as if a break in the stream which leads me to believe it is passing it correctly. Vorbis and MP3 playback had a very positive impression the first time I heard it from the nforce. I remember listening to a Dave Mathews Band MP3 and being very impressed with the audio quality. I can say that the nforce does some sort of DSP enhancement to the rear channels putting sound there that may not have been intended to be there in the original pro logic source but I can't confirm this.Any chance the software allows you to delay certain channels? I hear there is new versions of nforce drivers and since I built the nforce computer for my brother, I haven't had a chance to test the new drivers. The older ones had few if any options and no delay options IIRC.

[MCFish]

Well Matter, seems like he has same soundpicture as i had then....
Is hard to tell if nforce is encoding or not if u can not try same movie passed trough spdif as i should. Then u wouldnt know if it was right or wrong. For me it sounded like the ac3 from nforce was way off that im used too.
Same what he says about maybe rear channels have sound not meant to be there. Seemed that way to me too....
We need to sort these things out.

Emp3r0r: Hi, are u using a ac3filter like intervideo's iviaudio.ax or ac3filter? Eh remember u dont have it available now, but can u remember if u did use a ac3filter, in which u selected spdif?
Or did you just select spdif in the drivers controlpanel?

Fish

[MaTTeR]

Originally posted by MCFish
Well Matter, seems like he has same soundpicture as i had then.... Hrm..I might have misread it but I think pass-through is working fine. It seems to me if you turn off the "DD Encoding" tickbox then pass-through should be just fine. It wouldn't make sense for nVidia to make a board that always wants to re-encode an AC3 file. If that's the case I guess I could always stick the trusty Santa Cruz board in it :-)

The rear channel sound Emp3r0r mentioned was in regards to encoding a 2ch MP3/Vorbis file (Dave Matthews) to 5.1 AC3 using the nForce hardware. I think you said you heard the same effect when doing the 2->5.1 conversion.

Emp3r0r,
Correct me if I misunderstood your post. Thanks for your insight.

[OT] I wore my Bama hat to the Louisville game the other night, got some wicked looks from a few UK fans :D Roll tide!

[MCFish]

MaTTeR:
Yes, that makes sense about NVidia making it like that.
But all i know is that sound wasnt like it should be on that movie with DD encoding on. And when turning it off, amp lost the ac3 stream. Thats all i know :)

Yes it was a 2ch>5.1 i did,but ac35.1 also sounded wired to me.

Fish

[MaTTeR]

MCFish,

I know it will be a hassle but maybe you could try using AC3filter or Intervideo this time with an AC3. Without a proper DirectShow filter installed, I doubt the AC3 stream was being passed to your amp (Denon) properly. It's worth a shot;)

I'm off to work unfortunately...

[MCFish]

Matter:

yes, now i have to try it :)

Enjoy work, talk later.

Fish

[Emp3r0r]

The rear channel sound Emp3r0r mentioned was in regards to encoding a 2ch MP3/Vorbis file (Dave Matthews) to 5.1 AC3 using the nForce hardware. I think you said you heard the same effect when doing the 2->5.1 conversion. Right, for clarity, when playing back any non AC3 file, the nForce encodes it to AC3. Of course when playing an AC3 file you must have your AC3 filter set to SPDIF output for it to pass the bitstream correctly (which I'm positive it does). I really like the nforce and think that non AC3 material sounds great even if does seem to do some kind of surround enhancement to it. It makes a great sounding surround system come to life. I'm going to download and install the new drivers for my brother tonight and play some of those Dolby Digital trailers.

edit: [OT] Heh, I'm an Auburn fan and very much enjoyed beating Alabama this year in the Iron Bowl. War Eagle!