[Flac-dev] FLAC 24 bit test results

Josh Green josh at resonance.org
Thu Apr 5 09:48:06 PDT 2007

On Thu, 2007-04-05 at 02:27 -0700, Brian Willoughby wrote:
> Josh (Green),
> Seems like the longest example in your list is a 15-second file.  I  
> would like to see the same problem exhibited in a file that is of a  
> normal length.  I have been recording full performances lasting  
> hours, and flac always compresses the files below 70% of the original  
> size.
> Another thing to note is that "--best --no-padding" will not create a  
> file that is larger than the original.  Perhaps the only reason  
> you're seeing the file grow when flac-compressed is that you're  
> allowing the default padding to add to the file size.  I am not  
> familiar with WavPack, but perhaps it does not add empty padding for  
> metadata.
> One of the other volunteers looking at this problem produced a 3- 
> minute track that was supposed to have the same problem, but it ended  
> up compressing quite well ... 58% of the original size.  He's looking  
> into why he remembered having problems in the past.
> If we can't reproduce this problem with normal-sized songs, then  
> perhaps the best solution is to recommend that users simply turn off  
> padding if they need to compress extremely short audio samples.
> Brian Willoughby
> Sound Consulting

Yes, it would be nice to have some longer poor test cases, I'll see if I
can come up with something.  I've got lots of 24 bit samples I've
recorded, but a lot of them contain lots of silence, so I'd expect them
to compress well.

It seems that generally Wavpack does a little better than FLAC at
compressing audio.  But that is generally within a rather small margin.
20% margin seems a little large to me though.  There may indeed be no
problem with the FLAC reference implementation in regards to 24 bit and
its just having trouble compressing certain types of audio that Wavpack
does much better on.  But I think its worth having an understanding of
what exactly is going on, in case there is something that can be
improved in the FLAC reference implementation.

I'll see about finding some larger poor compressing examples.
	Josh Green

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