LPCM=PCM=WAV=CD ?? Techies HELP!?

[RWANDREWS]

Techies please clear up my confusion. It is my (mistaken?) impression that LPCM files are the same thing as PCM which are the same as .WAV which are the same as CD files.

Is there a real difference between them? Someone on another thread said PCM is a compressed format. It it so?

Is it possible to directly encode a CD soundtrack on top of a .m2v video file & have it be DVD compliant? What would have to be done , if not?


--Questions, questions, questions flooding the mind of the concerned young person of today.--Frank Zappa

[uxbridge]

LPCM stands for Linear PCM.
DVD video supports linear PCM tracks at 16 to 24 bits at 48 Khz sampling. PCM stands for Pulse Code Modulation in general and allows lower resolution and sampling such as CDDA.

A WAV file is the format PCM data is converted into file without any compression. PCM is usually uncompressed although some deviations can feature some sort of compression such as ADPCM.

You can encode a CD soundtrack (16bit PCM @44Khz) into a DVD linear PCM track, however you'll use a lot of disk space and you'll have to upsample from 44 Khz (standard CD) to 48 Khz. One way to do it is to rip the CDDA to wav(s), and then use an audio editor (Goldwave, CoolEdit...) to upsample.

Ciao

[Cornucopia]

The WAV file format is a type of RIFF header/container file. So basically, waves look like this:

[WAV Info Header][WAVE Data..............................][Wave Footer?]

The WAV data is usually PCM data, specifically Linear PCM, but it can be other things (ADPCM, Mp3, AC3, DTS, other codecs).

So, barring certain exceptions, LPCM=PCM=CDDA and WAV=PCM+wrapper.

This is also true of AIFF files, although the bytes are reversed.

Scott

[EddyH]

PCM = LPCM (maybe a slight difference in the dynamic response mapped onto it, but still PCM)
PCM also = CD
LPCM = CD-style audio on a DVD
WAV = general purpose sound file that can contain pretty much anything, much like an AVI. However in general use it contains uncompressed PCM audio - not always cd quality, often far worse - so yes.

Other common things you may find inside WAVs...
MP3s, as MP3-Wavs (a useful halfway house for inserting mp3s into vanilla virtualdub)
ADPCM, ADvanced PCM, dont know why they called it that. A very old and basic form of compression, slower to encode than MP3 but far faster on decode. Only about a 4:1 compression though (basically, 16 bits down to 4), like making 352kbit mp3s for CD stereo, or 64k for mono voice recording.. Two flavours, Microsoft and IMA (erm).
((Possibly ADPCM is what you were getting confused with))
A-law and mu-Law - even older, less efficient compressions. Squish 16 bits into 8. A bit useless really.


Compressed sound on DVD is either MPG1 (as in MP2), AC3 (dolby digital, MPG2?), or DTS.

[Cornucopia]

EddyH, you're pretty much stating the same thing I just said, but you're off-base with ADPCM.

It stands for: Adaptive-Delta PulseCodeModulation.
It's supposed to be a way to give very close to the same quality and resolution as PCM, but with much less bits being used. However, in practice there are problems with noise vulnerability and lack of editability along with the quality never getting quite there.
And now there are much better lossless and lossy compressed audio
formats that are smaller and yet still sound better. It is NOT slower to encode--I find it much faster--especially if you're trying to make your file have the highest perceived quality that it can for that bitrate.

There are other types of "modulation":
Delta-Modulation, Pulse-Width Modulation, Sigma-Delta Modulation (as used in DSD/SDDS/SACD I believe)...

And A-law and mu-law have their non-useless place, even today. Part of my work is doing phone-on-hold messages and music. Much of that is mu-law files on compact-flash chips now (used to be cassette loops).

Making sure the right story gets put out...(sorry for the dig)
Scott