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In Reply to: RE: In my mind there is only one way to compare format (a) to format (b) posted by rrob on February 17, 2015 at 04:02:20:
It is possible to compare formats indirectly without doing any decimation or even format conversion. One keeps the original sampling rate and provides the filtering that would have been used prior to the decimation into the lower sampling rate. This was done in a recent AES study by people from Meridian Audio.
"I believe that you can't compare A to B when B is a byproduct of A through sample rate / format conversion."
This is precisely what one does when one compares a live microphone (or tape feed) with a digital capture and playback. Analog as a "quasi-infinite" sampling rate. The advantage of doing digital comparisons is that extra analog stages and their distortion are avoided. The disadvantages of doing digital comparisons is that there will be some loss in resolution involving the double conversions, depending on their bit depth. Digital comparisons are best done where the format A has much higher resolution than format B.
In these experiments it is best to change only one variable at a time, e.g. sampling rate, while keeping the bit depth large. Or bit depth while keeping the sampling rate fixed. One also needs software converters that are transparent, i.e. can take a low res file, convert it to a hi-res file and then convert it back to the low res file and get the same (or at least very close) low res file.
However you do it (hardware or software) the results you get will depend on the particular filters chosen and the particular recordings used. Therefore, if one wants to rig a test to make a format sound bad, this is easily done. I prefer to work with digital conversions because this way I have complete control over the filters used and I know for certain that all the mastering is identical in both versions. If one works off of commercially provided versions where someone else has done the conversions, one is taking the vendor's word as to what was done. Of course, from the engineer's perspective who did the actual work this issue doesn't arise. I think this may be the bigest reason for the two sides to this argument.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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Follow Ups
- RE: In my mind there is only one way to compare format (a) to format (b) - Tony Lauck 02/17/1517:43:59 02/17/15 (2)
- RE: In my mind there is only one way to compare format (a) to format (b) - Presto 08:53:32 02/18/15 (1)
- RE: In my mind there is only one way to compare format (a) to format (b) - Tony Lauck 10:57:27 02/18/15 (0)
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