AC3 2.0 downmix

[mumdigaueln]

Hello,

In general, I author my DVDs with AC3 2.0 audio tracks preserving Dolby Surround information if available.

Recently, I streamed a movie with two audio tracks: First is Dolby Digital (AC3 5.1), second MPEG2. I see two possibilities:

1.) AC3 5.1 to AC3 2.0 downmix. For quality reasons, I don't like BeSweet and ffmpeg. Can anyone recommend a transcoder with excellent/very good quality?

2.) MPEG2 to AC3 2.0 encoding. I've got a very good encoder (Sonic Audio Transcoder from Scenarist).

But how do I determine if the MPEG2 stream is Dolby Surround or pure stereo? If it's Dolby Surround I'd encode the MPEG2 stream, otherwise I 've to downmix the Dolby Digital stream.

Many thanks for any info.

mumdigaueln

[Kisa_AG]

1.) AC3 5.1 to AC3 2.0 downmix. For quality reasons, I don't like BeSweet and ffmpeg. Can anyone recommend a transcoder with excellent/very good quality?

Try Sonic Foundry Soft Encode. It has an option to decompress ac3 to WAV PCM with downmixing. And it's a Sonic product with native Dolby engine, so it'll do your job with the best quality. Then encode this stereo WAV to ac3 with your Sonic Audio Transcoder. It's definetely the best ac3 encoding software.

PS: By the way, why don't you want to leave ac3 5.1 track as it is? I think it's the best way....

[mumdigaueln]

Try Sonic Foundry Soft Encode. It has an option to decompress ac3 to WAV PCM with downmixing. And it's a Sonic product with native Dolby engine, so it'll do your job with the best quality. Then encode this stereo WAV to ac3 with your Sonic Audio Transcoder. It's definetely the best ac3 encoding software.

PS: By the way, why don't you want to leave ac3 5.1 track as it is? I think it's the best way....

I used Sonic Foundry Soft Encode until 3 months ago for encoding wav to ac3 2.0. But it didn't work with large wav files (several GB), so I switched to Sonic Audio Transcoder (part of Scenarist). I wasn't aware that Sonic Foundry Soft Encode can also transcode ac3 5.1 to 2.0. Thanks for the info.

Do you have an answer to my 2nd question, as well: How to determine if a layer 2 mpeg stream is dolby surround encoded?

To answer your P. S. is quite simple: In general, I leave ac3 5.1 as it is and let the dvd player downmix it to 2 channel (I do have only stereo equipment). But at the moment I have a dvd project with two movies which only fit on a dvd if I replace the ac3 5.1 streams by ac3 2.0.

mumdigaueln

[mumdigaueln]

@Kisa_AG

I just reinstalled Sonic Foundry Soft Encode. I then loaded the AC3 5.1 file (decoded to wav) which surprisingly ended up with a two channels wav. As decode option I used 'source input mode', so I'd expect it will show up with six wav channels which I then could downmix to AC3 2.0 as desired.

Did I miss something?

mumdigaueln

[Kisa_AG]

I just reinstalled Sonic Foundry Soft Encode. I then loaded the AC3 5.1 file (decoded to wav) which surprisingly ended up with a two channels wav. As decode option I used 'source input mode', so I'd expect it will show up with six wav channels which I then could downmix to AC3 2.0 as desired.

Did I miss something?

Yes, it seems to me that you've missed to setup proper decode settings. Go to Options->Decode settings and setup what you need at Audio Coding mode line. If you will set "Use source coding mode" than you'll get as much channels as your AC3 file contains. If you will set 2.0, than you will get downmixed stereo file. etc.

[mumdigaueln]

Yes, it seems to me that you've missed to setup proper decode settings. Go to Options->Decode settings and setup what you need at Audio Coding mode line. If you will set "Use source coding mode" than you'll get as much channels as your AC3 file contains. If you will set 2.0, than you will get downmixed stereo file. etc.

That is exactly what I did : I used "Use source coding mode", input is AC3 5.1 (checked that with DVDMaestro and HeadAC3he: both report 6ch Dolby Digital), but file opens with two wave tracks (left and right). 'Stream settings' show

Audio Coding mode: 2/0 (L, R) Dolby Surround encoded

I really don't know what Soft Encode is doing here.

mumdigaueln

[Kisa_AG]

That is exactly what I did : I used "Use source coding mode", input is AC3 5.1 (checked that with DVDMaestro and HeadAC3he: both report 6ch Dolby Digital), but file opens with two wave tracks (left and right). 'Stream settings' show Audio Coding mode: 2/0 (L, R) Dolby Surround encoded
I really don't know what Soft Encode is doing here.

I don't know. I always believe Sonic products. Do you have Scenarist or DVDLab? If so please try to test with these programs. Even beter is to test it on the real Dolby digital reciever.

PS: But it can be wrong ac3 stream. Let's say it's a real 5.1 stream but the stream information is 2.0. If so, you need to find a way to edit it...