[Flac-dev] Idea to possibly improve flac?

Brian Waters brianmwaters at gmail.com
Fri Jan 7 21:38:54 PST 2011

> My 16-bit detector does exactly that, except that it only looks for
> 0x00 in the lowest 8 bits of each sample.

What if the program that did the 16-to-24 conversion also did some
dithering? If I'm not mistaken, that would probably be the case if
they did some sample rate conversion as well (maybe they were going
from CD quality up to 24/96). In that case, shouldn't your program
look for values in the LSB that are under a certain threshold, instead
of just zeros?

Again, forgive me if I'm misinformed here, this isn't really my specialty.

- BW

On Sat, Jan 8, 2011 at 12:31 AM, Brian Willoughby <brianw at sounds.wa.com> wrote:
> On Jan 7, 2011, at 18:08, Declan Kelly wrote:
>> On Fri, Jan 07, 2011 at 05:11:26PM -0800, brianw at sounds.wa.com wrote:
>> [NIN 24/96]
>>> Thanks!  That's interesting to note.  I think that I ended up with
>>> the true 24/96 files, but I am curious: How do you tell whether you
>>> have the full 24/96 or not?
>> Extract to WAV, do a hex dump, and look for repeated 0x00 bytes.
>> Someone
>> on the hydrogenaudio forums did that, reported it on the NIN
>> forums, and
>> Reznor got the reissued 24/96 FLAC'd and seeded on tracker.nin.com
>> in a
>> couple of days.
> My 16-bit detector does exactly that, except that it only looks for
> 0x00 in the lowest 8 bits of each sample.  I used to use hexdump, but
> didn't trust my eyes when scanning manually.  With a program, there
> aren't any false positives for 0x00 bytes in other positions.  What
> it does is scan until the first sample is found with something in the
> lowest 8 bits, and then reports the file as true 24-bit and quits
> early.  If it scans the entire file without finding any 24-bit
> values, it gives the sad news that it's really 16-bit samples
> disguised as 24.
> By the way, I had to special-case 0x00800001 and treat it as 16-bit.
> I don't know whether it was the MOTU 896HD or Logic, but something
> was creating that one value in the midst of an otherwise 16-bit pure
> file.  But there are tens of millions of other 24-bit values, so
> ignoring that one won't create a false report.
>>> 16-bit audio samples stored in a 24-bit file format.  Frequency
>>> analysis makes it obvious whether the content extends above 20 kHz.
>> Google for that hydrogenaudio thread: Reznor made one post on it, and
>> mentioned that the recording was done at both 24/96 (Lavry) and 24/192
>> (Apogee) on all songs, and they chose whichever they preferred at mix
>> time.
> Thanks.
> Brian
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