ALAC to FLAC conversion - big size difference

[doginabag]

I am currently trialling dBpoweramp to see if I can use it to convert my iTunes ALAC library to FLAC and avoid re-ripping all of my CD's. It's taking a while to work out the naming stuff but I think I am getting there, so decided to have the first go at converting he entire library.

The iTunes library is 180Gb, but the FLAC equivilent after conversion is 480Gb. Does that sound right, is FLAC that much less efficient?
The only setting I can see is for the lossless encoding. I set that to uncompressed thinking that as the files were already in a compressed but lossless format that should be ok, but I am now thinking I have that wrong.
Now I think more about it, as FLAC is a lossless compression, why are their various levels of compression available?

[Dat Ei]

Re: ALAC to FLAC conversion - big size difference

You mix up lossless data compression (like flac or zip) and lossy audio compression (like mp3).


Dat Ei

[garym]

Re: ALAC to FLAC conversion - big size difference

You mix up lossless data compression (like flac or zip) and lossy audio compression (like mp3).


Dat Ei

Correct. You chose "uncompressed" FLAC, which is basically the same size as a WAV (uncompresssed) file. So it will be more than double the size of your ALAC files. That's not what you want. All levels of a FLAC file are LOSSLESS. The encoder has to work a bit harder to encode with more compression (compression, NOT lossy as Dat Ei points out, these are different things). But on the decode (playback) side, it doesn't matter. I personally use the FLAC "5" level compression. Good compromise between file size and time to encode. (note that the "uncompressed" FLAC seems to be the dbpa developer providing an option for the audiophiles that (mistakenly) think that even FLAC lossless compression is affecting sound quality on playback. Basically like giving a sugar pill to hypochondriacs. ;-)

[doginabag]

Re: ALAC to FLAC conversion - big size difference

You mix up lossless data compression (like flac or zip) and lossy audio compression (like mp3).


Dat Ei

Correct. You chose "uncompressed" FLAC, which is basically the same size as a WAV (uncompresssed) file. So it will be more than double the size of your ALAC files. That's not what you want. All levels of a FLAC file are LOSSLESS. The encoder has to work a bit harder to encode with more compression (compression, NOT lossy as Dat Ei points out, these are different things). But on the decode (playback) side, it doesn't matter. I personally use the FLAC "5" level compression. Good compromise between file size and time to encode. (note that the "uncompressed" FLAC seems to be the dbpa developer providing an option for the audiophiles that (mistakenly) think that even FLAC lossless compression is affecting sound quality on playback. Basically like giving a sugar pill to hypochondriacs. ;-)

Thanks guys, poor understanding on my part then. I shall re-run the conversion and see how I get on.

[doginabag]

Re: ALAC to FLAC conversion - big size difference

And just to confirm, I re-ran it at the highest compression and virtually matched the ALAC folder size.

[Dat Ei]

Re: ALAC to FLAC conversion - big size difference

Hey doginabag,

Thanks guys, poor understanding on my part then.

just for your understanding of those two different kind of compression:

1) data compression (lossless)

This is a method we see in file types like flac or zip. An algorithm looks for the possibilty to reduce the file size by finding data patterns which can be found several times in the original file, and which can be described in a shorter way. I.e.: instead of writing 1000x "Don't drink and drive." in a row, which would be around 24.000 characters long, one could write A="Don't drink and drive.", 1000*A, which is only 32 characters long. As you see you can convert both forms forth and back without the loss of any information. This is just a very simpel example to transport the idea. In real life things are evene more complicated.

2) compression by reducing the content (lossy)

This is a method wee see in file types like mp3 or jpg. An algorith analyses the content and throws away information which is unnecessary from the point of view of the algorithm. In case of mp3 this can be frequencies which are assumed to be not hearable or to quiet to be heared by an average guy. But once the algorithm has thrown away this information you can't reproduce those information, i.e. if you try to convert it back to the original file format.
Those techniques are not bad in general, but you should make up yourmind, what you want and what you are up to. If you rip your CDs, a lossy target format is a no go. If you convert your lossless audio files for your iPod or car stereo, a lossy format is ok.


Dat Ei