acquiring digital music

[Joseph Sinclair]

FLAC does indeed run about 50% the size of a WAV file (at least all of my FLAC files are around 50-55%), although not for the reason you're citing.  There is a comparison of lossless codecs at (http://flac.sourceforge.net/comparison.html) which includes a comparison of compression ratios, and most of the lossless codecs run 40-50% of original filesize (which makes sense, since it's fairly easy to show that LZ compression is canonical WRT typical audio data in WAVE format using LPCM coding, so any lossless codec should produce results similar to LZ compression of a WAVE file, or around 50% compression).  Note that if the WAVE uses a different coding (such as ADPCM, µ-Law, or A-Law), the compression ratio may differ significantly.

For the common LPCM encoding, the specification at (http://www.tactilemedia.com/info/MCI_Control_Info.html) indicates that only a single sample is stored for each channel for each sample interval.

On a CD, Reed-Solomon encoding is used to introduce error correction, this is far more space-efficient than doubly encoding each sample, and actually catches, and corrects, more errors. (In fact two RS codes are used, RS(28,24) followed by RS(32,38) meaning there is a 33% overhead for ECC on a CD)
On a CD as much as 13% of the data can be damaged and the CD will still play correctly. There's a good discussion of RS encoding on CD at (http://66.102.7.104/search?q=cache:ogabeH3HliwJ:web.usna.navy.mil/~wdj/reed-sol.htm+CD+Reed-Solomon&hl=en) (google-cache, since the original seems to be gone)

Note, WAV is actually a RIFF file containing audio data, CD's do not, technically, contain WAV files, they contain CD tracks which are encoded as LPCM samples with error correction directly on disc, not using any container file format.

==Joseph++

der.hans wrote:
> Am 06. Oct, 2005 schwätzte Dragos Neagu so:
> 
> 
>>On 10/6/05, Craig White <craigwhite at azapple.com> wrote:
>>
>>>Flouting my laziness - now that I have an ipod and actually have started
>>>to learn what WAV - AAC - MP3 formats are - does anyone want to tell me
>>>what FLAC is?
>>>
>>>Craig
>>
>>http://www.vorbis.com/ (flac in the top right)
>>flac, in short is a lossless compression (iirc, ~70% the size of a WAV file)
> 
> 
> 70%? Hmm, I was told ( the FAQ doesn't say, though ) that WAV files have
> two data points for each piece of data and the average is used. This
> supposedly makes it somewhat scratch resistant because both pieces of
> data have to be wiped out to lose that chunk. FLAC then is supposedly the
> average of those two points ( and therefore 50% the size of WAV ) as you
> shouldn't be losing part of a digital file :).
> 
> Heck if I know...
> 
> ciao,
> 
> der.hans