[Flac] 24 bit question

[scott brown]

I meant -15.3 RMS and -.3 peak.

And bingo, you were correct in your last guess.  I feel dumb for not
thinking of it myself.  He's using a 24 bit interface, but he must not be
outputting 24 bits because when I tested the file, it's only actually 16
bits of audio.  Next time, that's the first thing I'm checking :)

Thanks again for all the help.  I knew something about this didn't seem
right...

Scott

On Thu, Dec 2, 2010 at 6:38 PM, Brian Willoughby <brianw at sounds.wa.com>wrote:

>
> On Dec 2, 2010, at 14:53, scott brown wrote:
>
>> original 24/48 wav file: 264,904,968 bytes
>> flac level 8: 105,992,780 bytes
>>
>> dithered 16/48 wav file:173,885,996 bytes
>> flac level 8: 108,700,948 bytes
>>
>> truncated 16/48 wav file: 173,885,996 bytes
>> flac level 8: 105,224,448 bytes
>>
>> RMS level of original 24 bit: -15.3dB with peaks at -0.3dB
>>
>> if I normalize the original file to a max of 0.0, the resulting flac file
>> is 192,798,482 bytes. weird....
>>
> Normalizing will probably always make the FLAC larger.  Of the many
> components of the FLAC algorithm, one is to use differential values rather
> than absolute, and another is to use variable-length coding (Rice coding).
>  Quieter files have smaller differential sample values, and thus compress
> more.
>
> I am surprised that a mere 0.3 dB normalization would add over 80% to the
> FLAC size.  Perhaps you missed something?  Can the RMS level actually reach
> -0.3 dB without serious distortion?  ... or did you mean -15.3 dB RMS and
> -0.3 dB PPM?
>
> Comparing the 24-bit WAV to the 16-bit WAV, it looks like as much as 4 MB
> of non-audio data is in the file.  You may be looking at waveform overviews
> or other extra chunks in the WAV file which are usually discarded by FLAC.
>  But this only explains a small part of the surprising numbers.
>
> One thing that stands out to me is that your original 24/48 WAV may not
> actually have 24-bit samples in it.  I wrote a program which could detect
> this situation (16-bit samples in a 24-bit file), but I do not know of any
> other available tool to test this.  It seems very suspicious that the 24-bit
> FLAC and truncated 16-bit FLAC are within 0.73% of each other (i.e., less
> than 1%).  I have a suspicion that your friend is recording 24-bit files
> from a 16-bit A/D converter interface, or at least the software is set for
> 24-bit files while the interface is set to 16-bit mode.  You should have the
> recordist double-check all settings.  A mistake here would easily explain
> the strange FLAC compression ratios.
>
> Brian Willoughby
> Sound Consulting
>
>
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