On 5/7/14 11:04 PM, Bjorn Roche wrote:
I've never heard this phenomenon myself, but I am familiar with it. It is a
psychoacoustic phemonen, and I've heard it referred to as "choo-chooing",
though when I just googled for that I got nothing related, so maybe that's
just a colloquial term amongst the engineers I know. I've never come across
it in any of textbooks on the subject, though I'm sure there are papers
written about it.
Some early hardware dithers found it cheaper to store a table of numbers in
ROM than to calculate random numbers with a PRNGs [1]. Because memory was
so expensive at the time, the length of the loop was chosen to be just long
enough to avoid the "Choo-Choo"ing phenomenon. If I remember correctly from
what the designer of one of those dithers told me, the length of repeat
that causes choo-chooing is very nearly the same for everyone, so it was
pretty each to choose the appropriate loop length. It would be cool to have
a WebAudio demonstration and/or test of this, as Chinmay Pendharkar
suggested.
bjorn
[1] You may have noticed early dithers made vague and strange marketing
claims. Like, "this is not a real dither, but a signal", or "not a dither,
but a bitmapping/bit-reduction scheme" or that they were somehow different
from or better than dither,
i know that products like apogee UV22 made such a claim.
even though the effect is exactly the same (or,
if anything, arguably worse, because no engineer with access to a halfway
decent PRNG would use a LUT).
there was a way that you could do "subtractive dither" in that the
dither that you added before quantizing to a short word could be
subtracted (to regain 4.77 dB) on the other end because the RNG would be
straight logic based on the LSB of the past, say, 256 words. now i
understand how both the quantizer and the later playback or processing
device (with a wider word) can get their dithers synchronized so that it
can be subtracted, but i wonder of the dither would be good dither,
doing that.
How the marketing departments of these
companies managed to turn the liability of not having a PRNG into an asset
is just proof that the marketing departments of these companies are a bunch
of mindless jerks who'll be the first against the wall when the revolution
comes.
On Wed, May 7, 2014 at 10:10 PM, Eden Sherry<e...@eden2.com> wrote:
Should standardize the sampling rate as well. With an infinite sampling
rate and your method, you'd have something like a pure broadband "tone",
right?
On May 7, 2014, at 5:39 PM, Sampo Syreeni<de...@iki.fi> wrote:
This is going to sound pretty weird, I'm sure, but could as many people
on-list perform the following experiment on themselves and their close
ones, as possible? Then report back (privately, so as not to ruin the
surprise for everybody else?)
Take a long (at least 30 seconds and possibly more) sequence of truly
random (AWGN) noise, either from a very long period PRNG or from a primary
randomness source. Then starting with very long periods of over 10 seconds,
loop the noise,
when you loop the noise, is it a "butt-splice"? (i.e. no crossfade.)
i mean, it's just white noise and a bunch of totally random values.
would it make a difference?
curtailing the period of repetition. Dropping it, say,
200ms at a time at first, and in the end perhaps something like 10ms at a
time. When does your ear, perceptually speaking, start to say that the
noise repeats? Precisely?
I'd be interested in hearing what people on-list have to say about this
one. Especially the ones who are curious enough to find the precise limit
in milliseconds, and even subject their loved ones to the test.
Because, I mean, at least for me this was a total mindfuck, and if you
analyze it e.g. via the usual LTI theory of human hearing, the results do
not make any sense at all. I think, but I'm not too sure. Whence the
question. ;)
it's news to me that human hearing is LTI.
--
r b-j r...@audioimagination.com
"Imagination is more important than knowledge."
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