This is a very good question. Hopefully Teddy Ray may be able to help out with his very high powered friends.
I have been trying really hard to grasp the temporal resolution issue and have found it really difficult. It seems to have been kicked off in audiophile circles by the NOS dac bollocks and (separately and indirectly) by an article by Craven for AES about the desirability of apodising/ minimum phase filters [not quite the same thing I know]. These filters are somewhat in vogue although neither weiss nor briscasti seem to use them. Annoyingly I think that this is an incredibly difficult area and the basic digital electronics text books i have read have very little on it. Just to get things started here are a couple of thoughts [APOLOGIES I NOW REALISE I HAVE GONE OFF ON A BIT OF A RAMBLE BUT HERE GOES ANYWAY}- a. AFAIK there really isn't any evidence that we can hear above 20Khz (make that 15 for most of us) b. in order to be nyquist compliant before sampling at 44.1kHz (or downsampling to 44.1), the signal has to be band limited to 22.05kHz or lower. c. there is an issue about whether the effect of this band limitation could be audible. d. we were talking here about the band limation prior to the ADC (or resampling) NOT in your DAC. e. but wait! the band limitation at the ADC has been created by a number of processes starting with the mic and then (maybe the mixer etc and the tape if its an old analog recording. So in order to analyse out the effect of band limitation you have to look at this chain as a whole f. time domain and frequency domain analysis are basically two sides of the same coin -if you limit the max frequency you must have an impact in the time domain. g. but this expression temporal resolution is a real bugger. AFAIK it has no fixed meaning. It is bandied around by certain audiophiles as a possible peg o which to hang their belief that "digital" especially properly filtered digital doesn't sound good. h if you don't believe me check out the kunchur/ JJ debate in which Kunchur made an utter arse of himself, despite being a genuine physicist, when he suggested that "temporal resolution" was limited to the inter sample period. i strictly speaking looking at the OP it seems to me that the answer is that if there is no information in the original signal about 20Khz there cannot be any time resolution issue with 20kHz band limitation. This is because a proper filter should have no impact below the stop band. It is therefore trivial that there could not be any information loss. j. that answer might be a bit to smart arse though- the real question is whether, assuming there was information above 20KhZ in the original signal, the band limitation prior to sampling might still have some detectable effect on the signal. k Any band limitation must affect the signal in the time domain. In particular the maximum frequency determines the maximum steepness of the slope in the time domain. So the band limited signal has to be spread out in the time domain if higher frequencies are filtered out. BUT CAN ANYONE ACTUALLY HEAR THIS? IF THEY CAN HEAR THE DIFFERENCE BETWEEN FIKLTERED AND UNFILTERED, the IS ONE Sensible) FILTER BETTER THAN ANOTHER l. this is where we get into pre ringng an post ringing. IN order to make a filter which perfectly complies with nyquist it should in principle be a linear phase filter. This will spread out the signal equally in both directions (earlier and later) . But according to auipophile magazines this apparently means pre ringing and this is apparently bad. m I would love to see 1) a demonstration of how a real world signal is affected by a linear phase filter with a passband up to 20hZ or so and proper attenuation at nyquist. Weirdly I have not actually seen one 2) some evidence that people can hear the difference between the unfiltered and filtered signal and the difference between MP and LP filters.. -- adamdea ------------------------------------------------------------------------ adamdea's Profile: http://forums.slimdevices.com/member.php?userid=37603 View this thread: http://forums.slimdevices.com/showthread.php?t=93483 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
