[Flac] 24 bit question

[scott brown]

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....

Scott

On Thu, Dec 2, 2010 at 4:36 PM, Brian Willoughby <brianw at sounds.wa.com>wrote:

>
> On Dec 2, 2010, at 07:55, scott brown wrote:
>
>> My first thought was that the file had low levels (before he sent me the
>> file), but that's definitely not the case with this file.  There are many
>> peaks that reach 0dBFS.
>>
> Live, uncompressed music often has peaks that are 4 dB higher, or more,
> than a typical commercial CD.  Such peaks are brief, and would not really
> affect the total size of the FLAC file.  Really, the average level is what
> determines whether the FLAC file ends up being smaller than 50% as it is in
> this case.
>
>
>
>  He sent me the original wav this morning and I loaded it into Wave Editor
>> on OS X.  I dithered to 16 bit using MBIT+ (high/ultra setting) and saved
>> the 16 bit file.  I did nothing else (no normalizing or any other
>> processing).  I can't give you the 16 bit size right now since I'm at work
>> and the file is on my Mac at home, but I can report back tonight.
>>
>
> Impressive!  I have read many comments that MBIT+ is the best.  I've only
> recently licensed it myself, so I have not yet had time to form a personal
> opinion as to whether it is better than the dither that I have been using
> for years.
>
> No matter how good the dither is, though, it's still noise.  The human ear
> and brain system cannot hear MBIT+, but FLAC is just a mathematical process.
>  Dithering from 24-bit to 16-bit is equivalent to increasing the
> quantization noise by about 48 dB!  It's actually quite impressive that you
> can add 48 dB of noise and the FLAC file only increases in size by less than
> 2%.
>
> Thanks for the details.  I'm curious about the file size, but uncompressed
> WAV should be exactly as I predicted.
>
>
>
>  Whatever my process is, though, the guy who originally recorded the file
>> gets the same results with whatever method he uses to convert to 16 bit on
>> Windows.  I can ask him what his 24 > 16 bit process is.  I can also just
>> truncate the file down to 16 bit and report back on the resulting flac file
>> size.  Would you expect that flac file to be around the same size as the 24
>> bit?  In my experience, my 24/48 flac files are always substantialy bigger
>> than my 16 bit flac files, which is why this case confuses me...
>>
> Personally, I rarely pay close attention to the exact compression.  I'm
> happy just that FLAC is smaller and lossless.  But I am still curious about
> the various reasons why some files turn out bigger or smaller than others.
>  I tend to do everything in 24-bit, even final mastering, so I have not
> looked at 16-bit in a long while.
>
> I can say that DTS surround music disc, which is 14-bit data in 16-bit CD
> format, does end up with a FLAC that is almost exactly 87.5% of the WAV.
>  This makes perfect sense, because the DTS data looks like random white
> noise to FLAC, and the only thing FLAC can do is compress those 2 unused
> bits.
>
> It's tempting to look at the 24-bit to 16-bit conversion as simply dropping
> 1/3 of the data, since files are based on 8-bit bytes.  But one way to look
> at this is that FLAC deals with audio samples as if they were all 32-bit.
>  The 16-bit samples simply have more noise.  It will be interesting to see
> what happens with your 16-bit truncation test.  I would expect that the FLAC
> would only get smaller, not increase in size, if all you do is truncate.
>
> Fortunately, FLAC is quite smart about bit utilization, and can even detect
> 16-bit samples in a 24-bit file.  I don't think that's happening with your
> files, though, because I would expect the 24-bit FLAC to be around 33% of
> the 24-bit WAV if it actually only had 16-bit samples, instead of the 40%
> that you're seeing.  But I suppose that's always possible.
>
> Brian Willoughby
> Sound Consulting
>
> P.S.  I'm still curious where Nicholas came up with the 14% value.  Is that
> based on decibels, bits, or some other metric I haven't thought of?
>
>
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