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, 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). 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, 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. ;) > > -- > > Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front > > +358-40-3255353, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 > > -- > > dupswapdrop -- the music-dsp mailing list and website: > > subscription info, FAQ, source code archive, list archive, book reviews, > dsp links > > http://music.columbia.edu/cmc/music-dsp > > http://music.columbia.edu/mailman/listinfo/music-dsp > -- > dupswapdrop -- the music-dsp mailing list and website: > subscription info, FAQ, source code archive, list archive, book reviews, > dsp links > http://music.columbia.edu/cmc/music-dsp > http://music.columbia.edu/mailman/listinfo/music-dsp > -- --------------------- Bjorn Roche bjornroche.com <http://blog.bjornroche.com> @xonamiaudio -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp
