[flac-dev] some report on type 3 wav

Erik de Castro Lopo mle+la at mega-nerd.com
Thu Jan 21 22:09:18 PST 2016

Federico Miyara wrote:

> Dear all,
> I have a wav file that when I try to encode with the FLAC Frontend, I 
> get "ERROR: unsupported format type 3".

WAV format 3 is 32 bit IEEE float which is not supported by FLAC.

> When I open it with an audio editor I find it is 44100 / 32 bit.

32 bit *floating point* values. WAV files can also contain 32 bit (integer)

> I 
> requantized it to 16 bit using the default dither and then compressed it 

Maybe requantizing to 24 bit might have made more sense (and 24 bit PCM
is handled by FLAC).

> However, as a last attempt, I used Winrar on the original file and to my 
> surprise it was compacted to 79 Mb, only about 33% more than the FLAC 
> version representing a file with half the data.

If the orignal 32 bit IEEE float file had been normalized so that all
sample values are between -1.0 and +1.0 then the exponent part of each
floating point value (8 bits out of 32 bits) would have been identical
resulting in a very significant opportunity for a data compressor like
WinRAR to do it's work.

A much better (fairer?) comparison would be to compare how WinRAR compresses
a 24 bit PCM WAV file in comparison to FLAC.

Erik de Castro Lopo

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