Originally Posted by BIslander
To the OP - movie soundtracks are mastered as multichannel PCM, which takes up a lot space on a disc. In order to save space, without sacrificing quality, studios useless lossless data compression - essentially a zipping process. They feed the track into a TrueHD or dts-MA encoder, which squeezes it down to a smaller size. The decoder unsqueezes the file, turning it back into PCM that is bit-for-bit identical to the original soundtrack.
It is not correct to call TrueHD or dts-MA "uncompressed". They are codecs, an acronym meaning COmpressionDECompression. Similarly, it is not correct to call PCM "lossless." Lossless refers to the type of data compression used to reduce the size of the file and there's no data compression involved in a PCM file.
Thank you for clarifying this, BIslander.
I like the "zipping" analogy. For instance, I can ZIP (compress) a spreadsheet or word processing document and save 90% of space. But to view the document, I must UNZIP (decompress) to view in its normal "raw" state.
Image files, on the other hand, are already compressed. Well... some of them are :-)
Take a JPG image file, for example. I could take a few jpg images... and further compress them with ZIP. I don't save very much additional space at this point (since the image files are already compressed), but more useful is the fact I'm sending ONE "simple" file rather than several. Even so, I usually see a slight reduction in size too - so it is compacting them slightly further.
Back to Finding Nemo...
The lossy Dolby Digital track was high in quality @ 7-9 MBps.
The lossless Dolby True HD track was VERY high in quality @ 25-35 MBps.
The lossy DTS track played from the "DTS MA option" (probably the hidden easter egg for backwards compatibility)
was average in quality at 2-3 MBps.
It seems to me there really is no difference in sound quality between DTS-MA, and DtrueHD. Because there is no data compression involved (at all) with LPCM, I wonder if there can be a very slight noticeable difference (even with just a scope or other hardware equipment)... meaning... is it possible there may be some miniscule distortion from the compress / uncompress state? If the audio was analog, I would imagine that would be the case. But since it's digital, probably not. I heard some amazing audio tracks in LPCM that were incredibly BOLD with a lot of punch (i.e., Scorcese's THE DEPARTED for example).
The bottom line is that I was SHOCKED to how spectacular the audio track was from using the digital coaxial (and... hearing Dolby Digital 5.1 even though the audio file chosen was Dolby True HD 7.1/5.1 - lol).