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In Reply to: RE: HDtracks 24/96 download vs same ripped from remastered CD.... posted by John Elison on July 12, 2014 at 07:42:27:
"For a valid comparison, you need to use the same DAC for both sample rates."
You are absolutely correct. I have studied this matter in quite a bit of detail and have some more observations that may be useful to anyone interested in doing serious qualification of the various digital formats.
One also needs to examine the digital files and compare the (RMS) level of the two files, to verify that the levels are the same.(1) In addition, it would be a good idea to measure the DAC with test tones at both sampling rates to ensure that the DAC has identical gain when running at the two formats involved. The file measurement can be done using an audio editor such as Audacity. The editor can also generate test tones in different formats. A voltmeter can be used to measure the DACs gain while playing test tones at the different formats. For valid comparison, one must have levels matched to at least 0.1 dB, better 0.05 dB.
There is still a remaining issue, namely the identical DAC is running different DSP at the two speeds. So in the end one can not know whether differences one hears are due to artifacts of the DAC or the format. In addition, if one does not hear differences one can not tell anything, since the lack of differences could be a function of the original recording, the mastering, limitations in other system components or even the listener's lack of training, attention or hearing.
I have done tests starting with a very high quality 176/24 file and downsamping to 44/16 using the 64 bit iZotope SRC and the iZotope Mbit+ dither algorithm. I then use the same tools to upsample back to 176/24 format. This takes the DAC out of the comparison to the extent possible. In addition, because the iZotope SRC allows control over various downsampling and dither parameters, I was able to train myself as to the tradeoffs involved, i.e. better learn to hear just what the limitations of the 44/16 format are for acoustic orchestral music. However, even in this case, I am still stuck with inability to distinguish limitations of the software and the settings it supports and that I chose vs. limitations of the format itself. In addition, there is a nagging doubt that any differences that I hear might not be real sonic differences encoded in the file, but different artifacts created by the DAC and rest of my playback chain. (One example of an artifact that magnifies a tiny difference to a larger difference would be low level non-linearity in a ladder DAC or variation in noise level due to DC offset in a sigma-delta DAC.)
(1) There are various reasons why the two formats might have been released at different levels, even if the 44/16 CD was made directly off the 96/24 digital master by digital conversion.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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- RE: HDtracks 24/96 download vs same ripped from remastered CD.... - Tony Lauck 07/12/1408:40:27 07/12/14 (0)
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