I SO agree with 4), that when it comes to recorded & not synthesized (but
even synthesized in some cases actually - I've made additive synths and it's
a big CPU saver to avoid processing inaudible partials) audio, room noise is
so much above the levels we're debating, that it's a bit silly.
-----Message d'origine-----
From: Nigel Redmon
Sent: Friday, February 06, 2015 7:13 PM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Dither video and articles
Mastering engineers can hear truncation error at the 24th bit but say it is
subtle and may require experience or training to pick up.
Quick observations:
1) The output step size of the lsb is full-scale / 2^24. If full-scale is
1V, then step is 0.0000000596046447753906V, or 0.0596 microvolt (millionths
of a volt). Hearing capabilities aside, the converter must be able to
resolve this, and it must make it through the thermal (and other) noise of
their equipment and move a speaker. If you’re not an electrical engineer, it
may be difficult to grasp the problem that this poses.
2) I happened on a discussion in an audio forum, where a highly-acclaimed
mastering engineer and voice on dither mentioned that he could hear the
dither kick in when he pressed a certain button in the GUI of some beta
software. The maker of the software had to inform him that he was mistaken
on the function of the button, and in fact it didn’t affect the audio
whatsoever. (I’ll leave his name out, because it’s immaterial—the guy is a
great source of info to people and is clearly excellent at what he does, and
everyone who works with audio runs into this at some point.) The mastering
engineer graciously accepted his goof.
3) Mastering engineers invariably describe the differences in very
subjective term. While this may be a necessity, it sure makes it difficult
to pursue any kind of validation. From a mastering engineer to me,
yesterday: 'To me the truncated version sounds colder, more glassy, with
less richness in the bass and harmonics, and less "front to back" depth in
the stereo field.’
4) 24-bit audio will almost always have a far greater random noise floor
than is necessary to dither, so they will be self-dithered. By “almost”, I
mean that very near 100% of the time. Sure, you can create exceptions, such
as synthetically generated simple tones, but it’s hard to imagine them
happening in the course of normal music making. There is nothing magic about
dither noise—it’s just mimicking the sort of noise that your electronics
generates thermally. And when mastering engineers say they can hear
truncation distortion at 24-bit, they don’t say “on this particular brief
moment, this particular recording”—they seems to say it in general. It’s
extremely unlikely that non-randomized truncation distortion even exists for
most material at 24-bit.
My point is simply that I’m not going to accept that mastering engineers can
hear the 24th bit truncation just because they say they can.
On Feb 6, 2015, at 5:21 AM, Vicki Melchior <vmelch...@earthlink.net>
wrote:
The following published double blind test contradicts the results of the
old Moran/Meyer publication in showing (a) that the differences between CD
and higher resolution sources is audible and (b) that failure to dither at
the 16th bit is also audible.
http://www.aes.org/e-lib/browse.cfm?elib=17497
The Moran/Meyer tests had numerous technical problems that have long been
discussed, some are enumerated in the above.
As far as dithering at the 24th bit, I can't disagree more with a
conclusion that says it's unnecessary in data handling. Mastering
engineers can hear truncation error at the 24th bit but say it is subtle
and may require experience or training to pick up. What they are hearing
is not noise or peaks sitting at the 24th bit but rather the distortion
that goes with truncation at 24b, and it is said to have a characteristic
coloration effect on sound. I'm aware of an effort to show this with AB/X
tests, hopefully it will be published. The problem with failing to dither
at 24b is that many such truncation steps would be done routinely in
mastering, and thus the truncation distortion products continue to build
up. Whether you personally hear it is likely to depend both on how
extensive your data flow pathway is and how good your playback equipment
is.
Vicki Melchior
On Feb 5, 2015, at 10:01 PM, Ross Bencina wrote:
On 6/02/2015 1:50 PM, Tom Duffy wrote:
The AES report is highly controversial.
Plenty of sources dispute the findings.
Can you name some?
Ross.
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