What is "time resolution"?
Reply #65 – 2006-11-15 12:45:54
......... For example, if you have a bass drum and a high hat playing at the same time, most of the waveform excursion will be due to the bass drum (which will survive the 5.5kHz low pass filter), but the exact peak location will also depend on the "wiggles" in the waveform due to the high hat itself. These high frequency "wiggles" will be butchered by a 5.5kHz low pass filter, so the peak will move! The experiment cant not work, it is just designed to generate the surviving correlation distribution data, so that we can refer to data about different sample rates relative and absolute abilities to accurately record timings of discrete conditions in source. You restate the practical 'damage' done to 'time resolution' of isolateable conditions in natural sources (saying> the exact peak location will also depend on "wiggles" butchered by a 5.5kHz lowpass) Documenting the average degree of that 'butchery' is the purpose of the experiment, no more, no less.The only way you can be absolutely sure that it's a fair experiment, and that the low pass filter isn't significantly moving the peak by removing part of the signal that forms the peak itself, is to ensure that the low pass filter doesn't remove anything. - i.e. that the original doesn't contain any frequencies above 5.5kHz, or, to put it another way, that the downsampled version still satisfies Nyquist with reference to the original content. That is plainly not fair. You are assuming preconditions which mean only informationaly lossless downsamples are considerable. I think you are unwilling to broaden your examination of 'reality' to a degree which would qualify the objections I have made about reported subsample 'time resolution' capabilities. I have been talking about reality. When we want to know what the timing resolution of a pcm record is, we would fundamentaly compare the capabilites of a record to the full potential of an ideal source. The experiment would compare the capabilites of lower rates with higher rates. Presupposing all records in the higher rates must be additionaly bandlimited as lower rates, is not sensible. Fundamentaly the 11kHz pcm's potential to resolve detail 'should' seem to be 1/4 of the CDs 44kHz record. That would go, 44kHz pcm 'time resolution' = 4* 11kHz pcm 'time resolution' You are implying that these two things are directly proportional in a real and limiting sense, whereas, until you get to the absolute limit, many orders of magnitude better than the limits of human hearing, and many orders of magnitude better than anything we expect the system to achieve, the two things are completely independent. Now you are talking of psychoacoustics. That is an entirely different matter, "what differences could we hear". I described a process to generate the correlation data of timing of surviving conditions between fully utilised (non extraneously bandpassed) pcm sample rate records. The data will "scale" according to simple principles. The time resolution of 1 Hz will be equal to 1/44100th of the time resolution of 44100 Hz - there is no doubt about that relationship. A plot could be made of their distribution of correlation, perhaps it would tend to be a bell curve? for pink noise only? What would the limits of correlation be? In a suitably controlled version of your experiment (like mine) it wouldn't be a bell curve, it would be a single point! That would certainly be the case with the parameters you propose (44.1>192kHz). That would be the pointless version of the experiment - or rather one which just examines rounding error. I have the code mostly written to perform (comparison of different sampling rates time resolution of conditions with various sources) I will hold off finishing it until it is acknowledged here that it presents a valid investigation (if done accurately enough and naturaly -without flattering extraneous bandpassing) l8r, cg