TMPGenc common audio question

[james_stewart]

This is just a simple audio question from TMPGenc, when you are using the wizard and you select the DVD template you then can select different audio types one is mpeg 1 layer II and the other is PCM. What is the difference and what do these terms mean?

[ZippyP.]

PCM is uncompressed and takes up a lot of space on a DVD, up to 1 GB for a typical movie. Mpeg1 layer-2 is also called MP2 (kinda like MP3) and takes up a lot less space leaving more room for video. More room = higher bitrate = better video.

The only drawback with MP2 is that it isn't in the DVD spec if you're making an NTSC disk. Many DVD players (most?) will still play it, though I understand some Pioneer DVD players have problems

[james_stewart]

This is only if you're encoding the video and audio together right? what if you're encoding the video and the audio separately, is this audio comparable to AC3, (file size & quality?)

[FulciLives]

LPCM WAV audio has a fixed bitrate of about 1536kbps and provides the best sound quality of all DVD formats. However it takes up a huge amount of space and therefore many people don't use it.

MP2 uses a much lower bitrate. Usually 224kbps is the lowest setting you would want to use. The next setting is 256kbps then 320kbps and the max that MP2 can be is 384kbps which is pretty good quality. MP2 sound quality is not as good as LPCM WAV nor as good as AC-3 so when people do use it some prefer to use the highest setting which is 384kbps.

AC-3 is better than MP2 and when using a high enough bitrate can sound just about as good as LPCM WAV audio. AC-3 like MP2 can also range in bitrate with 192kbps usually being the lowest you would want to use. Some people will use a higher bitrate like 224kbps or 256kbps but since AC-3 compresses so well (better quality than MP2) you would never have to use anything higher than 256kbps ... at least for normal mono or stereo 2 channel sound. Note that most stand alone DVD recorders that record to 2.0 AC-3 format use 256kbps but most commercial DVD discs tend to use 192kbps although some will use 224kbps or even 256kbps

In short MP2 can sound good but it is not official for the NTSC DVD spec so you are much safer using either LPCM WAV audio or AC-3 audio.

TMPGEnc DVD Author has an AC-3 plug-in that will convert MP2 or LPCM WAV audio to AC-3 and does a very good job of it. That is probably the cheapest AC-3 encoding solution ... that actually works well.

- John "FulciLives" Coleman

[FulciLives]

One more thing I wanted to point out ...

Audio size is determined by the bitrate.

So MP2 at 224kbps will be the same size as AC-3 at 224kbps however AC-3 is a higher quality format so assuming a high quality audio source the AC-3 will sound better than MP2 when using the same bitrate.

- John "FulciLives" Coleman

[james_stewart]

if I have i have a wave file that I extracted using virtual dub and the source is 128k, then i convert it to AC3, can i upconvert it to 224 or should i just leave it at 128k?

[FulciLives]

if I have i have a wave file that I extracted using virtual dub and the source is 128k, then i convert it to AC3, can i upconvert it to 224 or should i just leave it at 128k?

I'm assuming the source was a MP3 audio file?

Well converting it to WAV format is more-or-less a good thing but it is overkill so yes I would convert to AC-3 and you definately don't want to go lower than 192kbps

Personally I use 256kbps for AC-3 audio encoding.

- John "FulciLives" Coleman

[james_stewart]

the source was a Divx movie with the audio at 128kb i then extracted the audio into a wave file (1.1 gb) then converted into AC3 but i left it at 128kb, should i of increased the bitrate to 224??

[FulciLives]

the source was a Divx movie with the audio at 128kb i then extracted the audio into a wave file (1.1 gb) then converted into AC3 but i left it at 128kb, should i of increased the bitrate to 224??

At the very least you should do 192kbps

Remember you have a heavily compressed (128kbps) audio file to begin with. You are then converting it to a WAV and now you are compressing it yet again to AC-3 format.

Guidelines say that even a very clean source should be 192kbps or more and yet you made your AC-3 128kbps

So you see what I'm saying?

Double compression. So use the least amount of compression that you can for the AC-3 format since this is compression number 2.

If it were me I'd do 256kbps AC-3

- John "FulciLives" Coleman