[flac-dev] some report on type 3 wav

Federico Miyara fmiyara at fceia.unr.edu.ar
Sat Jan 23 08:07:40 PST 2016


The file indeed reached +/- 1 (one channel is the output of a magnetic 
switched device, the audio signal is not strictly on-off but it has a 
characteristic pattern that saturates).

I performed the test you've suggested. I used Audacity to convert 
32-float to 24-signed. The original size of 347 Mb reduced to 260 Mb, 
the expected 3/4 reduction. Then I compressed it with FLAC, getting a 
120 Mb file, and with Winrar, getting a 54 Mb file.

However this may be an anomalous case, since I've tested other (16 bit) 
audio files and FLAC outperforms RAR.



On 22/01/2016 3:09, Erik de Castro Lopo wrote:
> 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)
> PCM.
>> 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

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