Any way to convert 24-bit PCM to a usable format?

[baseband]

I've run across a bit of an odd situation. I purchased a music video DVD and the AC3 audio is messed up. The volume seems to fluctuate randomly throughout the songs. I searched online, but nobody else seemed to be having any problems with the disc, so I don't know what to think. Everything else plays fine. The problem occurs both in WinDVD and on my standalone.


Well, I noticed the DVD also had a 24-bit PCM stream in addition to the AC3, with identical content. I tried ripping just the PCM audio with DVD Decrypter, which left me with a VOB file that played in WinDVD and sounded great. No weird audio quirks. On viewing the properties in WinDVD, I noticed that the program converted the audio to 16-bit on the fly.

So my plan was to convert the 24-bit PCM stream to 16-bit, then convert that to AC3 and re-author the DVD with the new, non-screwed-up AC3 audio. The problem is that I'm having tremendous difficulty finding a program that can do this.

Opening the 24-bit audio file in GoldWave and SoundForge just yields junk audio. A program called Awave claimed to support conversions of this type, but instead just churned out a file with 16-bits of the same junk audio heard in the other programs. I've tried extracting the audio with DVD Decrypter, Vstrip, and VOBrator, but always with the same results.

It seems that if WinDVD can do this on the fly, there would be programs out there to do the conversion, but I can't find them, or any kind of decent information on this subject.

I'm aware of audio capture programs for the PC, and I'm aware of the analog hole, but those are last resorts. I'd really like to get the DVD I paid good money for fixed right. Any help would be much appreciated.

[johns0]

One way you can convert to 16 bit is set your recording to `what you hear` and start recording with goldwave and start playing the music,it may be a slow way doing it in realtime but at least its a way til you find the proper conversion method.

[baseband]

Thanks for taking the time to reply, but that's simply capturing the audio. See the last paragraph of my post.

[awlchu]

big endian vs little endian?

Did you try both import mechanisms in Goldwave?

[petar]

Have you tried dBpowerAMP Music Converter? It has the option to convert 24bits to 16bits. I've never tried it because I've never needed it so I don't know if it works well. For what I use it (MP2 to WAV and change frequency 44.1kHz to 48kHz) it's really excellent and unbelievably quick.
Give it a try. It's free.

[baseband]

big endian vs little endian?

Did you try both import mechanisms in Goldwave?

I have no idea if it's big or little endian, or how to find out. Also, I didn't know that there was more than one input mechanism in Goldwave. The only way I can figure out to open files is File->Open. Searching for input in the Goldwave help yields nothing useful.

Have you tried dBpowerAMP Music Converter? It has the option to convert 24bits to 16bits.

I gave it a try, but, like Awave, it claimed to be able to do it, but just gave me a 16-bit junk file.

[awlchu]

baseband,

I believe Goldwave allows you to specify the byte order (big or little endian) for PCM files that do not have a legit header.

If you pick the wrong endian the display is not a sound wave but a block of trash.

big endian vs little endian?

Did you try both import mechanisms in Goldwave?

I have no idea if it's big or little endian, or how to find out. Also, I didn't know that there was more than one input mechanism in Goldwave. The only way I can figure out to open files is File->Open. Searching for input in the Goldwave help yields nothing useful.

Have you tried dBpowerAMP Music Converter? It has the option to convert 24bits to 16bits.

I gave it a try, but, like Awave, it claimed to be able to do it, but just gave me a 16-bit junk file.

[baseband]

Ah, okay, I understand what you mean now.

Well, between the various programs I've tried to extract the audio, I've gotten files with three different exensions: PCM, RAW, and WAV (headers added by smartripper).

When I load the WAV in Goldwave, it doesn't ask for any information, but I get the good 'ol block of trash. When loading the RAW, it asks, but I get trash whether I specify little -or -big-endian. Oddly, when I load the PCM file as big-endian, I get a left channel of music and a right channel of junk! When i load it as little, it looks like a few seconds is junk and the rest is okay on the left channel, and all junk on the right channel.

The same audio sounds fine in both channels in a VOB played in WinDVD.

[tompika]

ffmpegGUI ?

[baseband]

ffmpegGUI ?

RAW: "'Bad000' is not a valid integer value" error on loading file

PCM: "Floating Point Division by Zero" error on loading file

WAV: Produces another nice junk file, this one in non-compliant AC3!

[FOO]

You don't suppose it's 12 bit PCM in stereo ? 24 is ridiculous

[autodidact]

The nature of the problem as I understand it is that WinDVD supports Linear PCM, 24-bit or otherwise, when properly multiplexed in the VOB structure and can downsample as necessary for playback. Hence your ability to play the audio while still in the VOB file. However, once you de-multiplex the audio from the VOB it is basically a headerless Linear PCM file which does not contain the normal propeties information necessary for standard playback or conversion. There is a utility on the RareWares website called LPCM24 which will process the file into a standard wave from which you can then downsample and convert as required. It does require a careful and specific ripping procedure but the Readme.txt included walks you through it. I've had success with it.

Sorry for the verbose reply.

[baseband]

Sorry about the lateness of the reply. I was pretty busy yesterday.

You don't suppose it's 12 bit PCM in stereo ? 24 is ridiculous

I'm not terribly knowledgeable about digital audio. I'm just going by what it says in the properties for every program that sees this audio as something other than junk (e.g. WinDVD, ripping programs). If you'll check out WinDVD's web site, it claims to support the 24-bit audio, and the same claim is printed on the front of my friend's standone DVD player. It's apparently not too ridiculous for them...

The nature of the problem as I understand it is that WinDVD supports Linear PCM, 24-bit or otherwise, when properly multiplexed in the VOB structure and can downsample as necessary for playback. Hence your ability to play the audio while still in the VOB file. However, once you de-multiplex the audio from the VOB it is basically a headerless Linear PCM file which does not contain the normal propeties information necessary for standard playback or conversion. There is a utility on the RareWares website called LPCM24 which will process the file into a standard wave from which you can then downsample and convert as required. It does require a careful and specific ripping procedure but the Readme.txt included walks you through it. I've had success with it.

Sorry for the verbose reply.

Sorry? Hell, that's exactly the kind of knowledgeable information I'm looking for! Thank you so much for setting me on the right track! I'm going to check that program out as soon as I get a chance.

[FOO]

I've been misquoted. How did you do that.
24 bits in one channel IS ridiculous. I don't even think it's possible.