Two audio questions

[rotflol]

1. I have some DVDs that have mono sound, but the actual tracks are Dolby Digital 2.0. I feel that I could save some more bitrate for the video if I encoded these tracks as mono MP3 when doing XviD backups. Is this recommended and how do I do it in BeeSweet(GUI/Wizard)?
2. Is there a tool that can compare the channels in a stereo track and say if they're identical/duplicated?

[oddyseus]

all the Lame versions have a switch to downmix a stereo to mono file. I am sure one of them will produce an actual 1 channel audio.

As for the 2nd question, afaik only the visual method of comparison the 2 channels apply.

[manono]

Hi-

To elaborate a bit more, the switch is -m m. You can find it in the Lame 1 part of the GUI, Operational Options->Mode->Mono.

I find the second question much more interesting. Of course, all movies before a certain date used Mono audio, but the dates vary by country. IMDB can often tell you if the original audio was Mono. In addition, often the DVD makers redo the Mono audio for Stereo, and sometimes even DD 5.1, with varying degrees of success. I don't much approve of original Mono audio being reencoded for Stereo, but it's up to you whether or not to honor the change, or make it Mono again.

To find out what's on the DVD, I take a portion of the soundtrack (usually the opening, with some music), convert it to WAV, and have a look at it in a Wave Editor. For example, Cool Edit Pro, in the Analyze Tab, has both a Phase Analysis and Frequency Analysis which will help determine if it's true Stereo or just dual Mono. Often you can't tell just by looking at the waveform, or even by listening, as a true Stereo track is sometimes created from what was originally Mono, but with so little separation that you just can't tell with your ears.

Of course, there are benefits to reencoding dual channel Mono to single channel Mono, as you then free up a lot of bits to help improve the video quality. I do it all the time, and recommend it. Depending on how you play back your AVIs, you can get it playing through 2 speakers anyway, just the same as dual channel Mono. But I know of no way to do this for the AC3 (that is, just knocking out one of the channels, making it DD 1.0, playing through the center channel) without reencoding. If there is a way to do this, then someone please enlighten me. KpeX? So I convert to Mono MP3.

[rotflol]

Originally posted by manono
Hi-

To elaborate a bit more, the switch is -m m. You can find it in the Lame 1 part of the GUI, Operational Options->Mode->Mono.

Thanks, helpful as ever.

I find the second question much more interesting. Of course, all movies before a certain date used Mono audio, but the dates vary by country. IMDB can often tell you if the original audio was Mono. In addition, often the DVD makers redo the Mono audio for Stereo, and sometimes even DD 5.1, with varying degrees of success. I don't much approve of original Mono audio being reencoded for Stereo, but it's up to you whether or not to honor the change, or make it Mono again.

Yeah, well, with some movies it says 'Mono' on the cover, but others are just 'Dolby Digital 2.0'. I was thinking of asking around when in doubt; while IMDB might not help a lot (I mostly deal with Hong Kong DVDs), thanks for the suggestions, I'll play around with a WAV editor. Oh, and I know what you mean by 'varying degrees of success', some of those 5.1 mixes are downright horrid.

Of course, there are benefits to reencoding dual channel Mono to single channel Mono, as you then free up a lot of bits to help improve the video quality. I do it all the time, and recommend it. Depending on how you play back your AVIs, you can get it playing through 2 speakers anyway, just the same as dual channel Mono.

OK, just where would I not be able to play it through 2 speakers?

Thanks again, one more silly question: So when I reencode to Mono, I guess it's OK to use half the bitrate I'd use for Stereo, or maybe I shouldn't go below a certain limit?

[manono]

Hi-

When I load a Mono AVI into my DVD/MPEG-4 player, it outputs only to the center channel, until I turn on the surround. Sure, for PC playback, you'll get it out of both speakers.

Yes, you can use half the bitrate for Mono. I usually spread it between 32-96 or 112, and wind up with an average 70-80. But I'm far from an audio expert.

[rotflol]

Okay, it won't bother me on PC.
Thanks again!

[niamh]

I have a few of those Hong Kong DVD's ...I have encoded them in CBR 80 K mono mp3, and honestly, I can't hear a difference from the original (i.e. both tracks are horrible :D ). I'm sure it can be pushed lower than that if you need space. If you don't especially need mp3, you can try AAC "streaming medium quality"(IIRC) which is VBR 50-70 k and gives great quality, but don't ever use the downmix to mono button unless you like special effects ;)