Re: [music-dsp] Dither video and articles
32-bit internal floating point is not sufficient for certain DSP tasks and will be plainly audible as causing all sorts of problems, a DF1 at low frequencies is the classic example of this, it causes large amounts of low frequency rumble. This is a completely different thing to the final bit depth of an audio file to listen to. Andy -- cytomic -- sound music software -- On 7 February 2015 at 02:24, Michael Gogins michael.gog...@gmail.com wrote: Do not believe anything that is not confirmed to a high degree of statistical signifance (say, 5 standard deviations) by a double-blind test using an ABX comparator. That said, the AES study did use double-blind testing. I did not read the article, only the abstract, so cannot say more about the study. In my own work, I have verified with a double-blind ABX comparator at a high degree of statistical significance that I can hear the differences in certain selected portions of the same Csound piece rendered with 32 bit floating point samples versus 64 bit floating point samples. These are sample words used in internal calculations, not for output soundfiles. What I heard was differences in the sound of the same filter algorithm. These differences were not at all hard to hear, but they occurred in only one or two places in the piece. I have not myself been able to hear differences in audio output quality between CD audio and high-resolution audio, but when I get the time I may try again, now that I have a better idea what to listen for. Regards, Mike - Michael Gogins Irreducible Productions http://michaelgogins.tumblr.com Michael dot Gogins at gmail dot com On Fri, Feb 6, 2015 at 1:13 PM, Nigel Redmon earle...@earlevel.com wrote: 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 0.000596046447753906V, 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
Re: [music-dsp] Dither video and articles
On 7 February 2015 at 03:52, Didier Dambrin di...@skynet.be wrote: It was just several times the same fading in/out noise at different levels, just to see if you hear quieter things than I do, I thought you'd have guessed that. https://drive.google.com/file/d/0B6Cr7wjQ2EPub2I1aGExVmJCNzA/view?usp=sharing (0dB, -36dB, -54dB, -66dB, -72dB, -78dB) Here if I make the starting noise annoying, then I hear the first 4 parts, until 18:00. Thus, if 0dB is my threshold of annoyance, I can't hear -72dB. So you hear it at -78dB? Would be interesting to know how many can, and if it's subjective or a matter of testing environment (the variable already being the 0dB annoyance starting point) Yep, I could hear all of them, and the time I couldn't hear the hiss any more as at the 28.7 second mark, just before the end of the file. For reference this noise blast sounded much louder than the bass tone that Nigel posted when both were normalised, I had my headphones amp at -18 dB so the first noise peak was loud but not uncomfortable. I thought it was an odd test since the test file just stopped before I couldn't hear the LFO amplitude modulation cycles, so I wasn't sure what you were trying to prove! All the best, Andy -Message d'origine- From: Andrew Simper Sent: Friday, February 06, 2015 3:21 PM To: A discussion list for music-related DSP Subject: Re: [music-dsp] Dither video and articles Sorry, you said until, which is even more confusing. There are multiple points when I hear the noise until since it sounds like the noise is modulated in amplitude by a sine like LFO for the entire file, so the volume of the noise ramps up and down in a cyclic manner. The last ramping I hear fades out at around the 28.7 second mark when it is hard to tell if it just ramps out at that point or is just on the verge of ramping up again and then the file ends at 28.93 seconds. I have not tried to measure the LFO wavelength or any other such things, this is just going on listening alone. All the best, Andrew Simper On 6 February 2015 at 22:01, Andrew Simper a...@cytomic.com wrote: On 6 February 2015 at 17:32, Didier Dambrin di...@skynet.be wrote: Just out of curiosity, until which point do you hear the noise in this little test (a 32bit float wav), starting from a bearable first part? https://drive.google.com/file/d/0B6Cr7wjQ2EPucjFCSUhGNkVRaUE/view?usp=sharing I hear noise immediately in that recording, it's hard to tell exactly the time I can first hear it since there is some latency from when I press play to when the sound starts, but as far as I can tell it is straight away. Why do you ask such silly questions? All the best, Andrew Simper -- 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 - Aucun virus trouve dans ce message. Analyse effectuee par AVG - www.avg.fr Version: 2015.0.5645 / Base de donnees virale: 4281/9068 - Date: 06/02/2015 -- 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
Re: [music-dsp] Dither video and articles
Hi RBJ, Well, the point of dither is to reduce correlation between the signal and quantization noise. Its effectiveness requires that the error signal has given properties; the mean error should be zero and the RMS error should be independent of the signal. The best known examples satisfying those conditions are white Gaussian noise at ~ 6dB above the RMS quantization level and white TPDF noise at ~3dB above the same, with Gaussian noise eliminating correlation entirely and TPDF dither eliminating correlation with the first two moments of the error distribution. That's all textbook stuff. There are certainly noise shaping algorithms that shape either the sum of white dither and quantization noise or the white dither and quantization noise independently, and even (to my knowledge) a few completely non-white dithers that are known to work, but determining the effectiveness of noise at dithering still requires examining the statistical properties of the error signal and showing th at the mean is 0 and the second moment is signal independent. (I think Stanley Lipschitz showed that the higher moments don't matter to audibility.) Probably there are papers around looking at analog noise in typical music signals and how well it works as self dither (because self dither is assumed in some A/D conversion) but I don't know them and would be very happy to see them. The one case I know involving some degree of modeling was a tutorial on dither given last year in Berlin that advised against depending on self dither in signal processing unless the noise source was checked out thoroughly before hand. Variability of amplitude, PDF and time coherence were discussed if I recall. Best, Vicki On Feb 6, 2015, at 9:27 PM, robert bristow-johnson wrote: Original Message Subject: Re: [music-dsp] Dither video and articles From: Vicki Melchior vmelch...@earthlink.net Date: Fri, February 6, 2015 2:23 pm To: A discussion list for music-related DSP music-dsp@music.columbia.edu -- The self dither argument is not as obvious as it may appear. To be effective at dithering, the noise has to be at the right level of course but also should be white and temporally constant. why does it have to be white? or why should it? -- r b-j r...@audioimagination.com Imagination is more important than knowledge. -- 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
Re: [music-dsp] Dither video and articles
why does it have to be white? or why should it? A common and trivial dither signal for non-shaped dither is rectangular PDF noise through a one-pole highpass filter. In other words, instead of generating two random numbers and adding them together for the dither signal at each sample, one random number is generated, and the random number for the previous sample is subtracted. The idea is that it biases the noise toward the highs, less in the body of the music, and is a little faster computationally (which typically doesn’t mean a thing). On Feb 6, 2015, at 6:27 PM, robert bristow-johnson r...@audioimagination.com wrote: Original Message Subject: Re: [music-dsp] Dither video and articles From: Vicki Melchior vmelch...@earthlink.net Date: Fri, February 6, 2015 2:23 pm To: A discussion list for music-related DSP music-dsp@music.columbia.edu -- The self dither argument is not as obvious as it may appear. To be effective at dithering, the noise has to be at the right level of course but also should be white and temporally constant. why does it have to be white? or why should it? -- r b-j r...@audioimagination.com Imagination is more important than knowledge. -- 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
Re: [music-dsp] Dither video and articles
Hi Vicki, My intuitive view of dither is this (I think you can get this point from my video): After truncation, the error introduced is the truncated signal minus the original high resolution signal. We could analyze it statistically, but our ears and brain do a real good job of that. And after all, the object here is to satisfy our ears and brain. Listening to the original, high-resolution signal, plus this error signal, is equivalent to listening to the truncated signal. So, my question would be, given such an error signal that sounds smooth, pleasant, and unmodulated (hiss-like, not grating, whining, or sputtering, for instance): Under what circumstances would the result of adding this error signal to the original signal result in an unnecessarily distracting or unpleasant degradation of the source material? (And of course, we’re talking about 16-bit audio, so not an error of overpowering amplitude.) I’m not asking this rhetorically, I’d like to know. Measurable statistical purity aside, if the error doesn’t sound wrong to the ear, can it still sound wrong added to the music? I’ve tried a bit, but so far I haven’t been able to convince myself that it can, so I’d appreciate it if someone else could. Nigel On Feb 7, 2015, at 5:54 AM, Vicki Melchior vmelch...@earthlink.net wrote: Hi RBJ, Well, the point of dither is to reduce correlation between the signal and quantization noise. Its effectiveness requires that the error signal has given properties; the mean error should be zero and the RMS error should be independent of the signal. The best known examples satisfying those conditions are white Gaussian noise at ~ 6dB above the RMS quantization level and white TPDF noise at ~3dB above the same, with Gaussian noise eliminating correlation entirely and TPDF dither eliminating correlation with the first two moments of the error distribution. That's all textbook stuff. There are certainly noise shaping algorithms that shape either the sum of white dither and quantization noise or the white dither and quantization noise independently, and even (to my knowledge) a few completely non-white dithers that are known to work, but determining the effectiveness of noise at dithering still requires examining the statistical properties of the error signal and showing th at the mean is 0 and the second moment is signal independent. (I think Stanley Lipschitz showed that the higher moments don't matter to audibility.) Probably there are papers around looking at analog noise in typical music signals and how well it works as self dither (because self dither is assumed in some A/D conversion) but I don't know them and would be very happy to see them. The one case I know involving some degree of modeling was a tutorial on dither given last year in Berlin that advised against depending on self dither in signal processing unless the noise source was checked out thoroughly before hand. Variability of amplitude, PDF and time coherence were discussed if I recall. Best, Vicki On Feb 6, 2015, at 9:27 PM, robert bristow-johnson wrote: Original Message Subject: Re: [music-dsp] Dither video and articles From: Vicki Melchior vmelch...@earthlink.net Date: Fri, February 6, 2015 2:23 pm To: A discussion list for music-related DSP music-dsp@music.columbia.edu -- The self dither argument is not as obvious as it may appear. To be effective at dithering, the noise has to be at the right level of course but also should be white and temporally constant. why does it have to be white? or why should it? -- r b-j r...@audioimagination.com Imagination is more important than knowledge. -- 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 -- 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
