"z1x2c3v4z1x2c3v4",
I think a sine wave is not the best way to test a compression algorithm
since the only uncorrelated component is the quantizing error, which is
very small.
First of all, my test for a 100 % 440 Hz tone yields 24.10 % instead of
30.66 % as yours.
Second, for 16 bit, 44100 Hz the slope is so large that if the first
sample is 0 then the second sample is about 1854 (being 100% = 32767).
This means that atenuating it to a 5 % and then multiplying by 20
probably will recover the signal accurately.
But if instead of a full scale sine wave you generate a signal that
starts being a sine wave of an amplitiude equal to
10 / 32767 = 0.00030518
(equivalent to an amplitude -70.3087 dB)
and then, after, say, 10 s, follows a full scale (100 % = 0 dB) sine
wave, then you'll find that the decoded signal is different from the
original one if you apply your method, since normalizing to a anythig
but 100 % will render the first part severely and unrecoverably
distorted. And normalizing to a 5 % actually will make the signal
vanish, so no matter by how much you multiply it, it will keep being 0.
Federico Miyara
On 19/08/2017 18:37, z1x2c3v4z1x2c3v4 wrote:
Hi FLAC team.
I feel I have found a super high compression way of FLAC. I have
tested a 1 hour WAV file of 440HTZ with a 5,25,50,75,100 normalize
volume preset. This dramatically changes the compression size of the
end FLAC file even though the WAV file size is identical for all 5 WAV
files. Only the volume is different. When you renormalize the WAV to
its original volume the file is still 100% original.
My tests are the following.
source file WAV. 1 hour 440HTZ tone. 600MB.
volume at 100. FLAC file size is 184MB.
volume at 75. FLAC file size is 166MB.
volume at 50. FLAC file size is 143MB.
volume at 25. FLAC file size is 109MB.
volume at 5. FLAC file size is 96MB.
From184MB to 96MB.
As you can see from the full 100 normalize volume to the 5
normalize volume it is half the file size.
So to put it. I think that you should have your compression of FLAC to
also include a normalize volume shift to further compress the end
product. Either have a default setting or allow a user to input an
option in the command line arguments to add a normalize volume value.
Then to uncompress it back to a WAV file FLAC would read the volume
header in the FLAC file to apply the WAV original normalize volume and
expand it back to its original state.
Then have the FLAC decoder for all the players out there to read the
volume header so to play the FLAC at the WAV original normalize volume.
I hope I have helped to develop FLAC further.
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