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In Reply to: RE: Hey JimiAustin: MQA Enabled ADCs posted by Isaak J. Garvey on October 30, 2016 at 22:49:49
Isaak,
in one of the numerous MQA threads I posted that the biggest problem with MQA is that it is too clever for most to understand.
The real problem with MQA is that is, IMO, really two functions:
1. An end-to-end temporal response with minimal 'blurring', to use Bob Stuart's phrase.
2. An encoding scheme that reduces the file size/bit-rate to below that of conventional 'hi-res' files.
Maybe the implementation of the two functions are so intertwined that they are one thing. It certainly seems that all interviews and publicity treat it as one thing (maybe to its detriment?)
An ADC is still an ADC. The answer in the linked interview does not state there is anything special about the ADC function for MQA except 'low modulation noise', i.e. it should be a good ADC. So, in those terms, Jim was correct, your original question does not make sense.
What I think the talk of an MQA-enabled ADC is about is, at minimum, having a defined temporal response or, at maximum, building the encoding process into the ADC so that output data rate is already reduced and the metadata included for the decoder to know what reconstruction filter response to adopt to compliment the ADC without the need to add that during mastering.
Regards
13DoW
Follow Ups:
There is one other consideration, which is at least slightly relevant to this discussion. MQA has implemented a procedure where, during recording, they basically collect a fingerprint of the ADC, if you're doing the ADC conversion in anticipation of transcoding to MQA. Not sure if this is just an impulse response test, but that would make sense. Anyway, that information makes it very simple for MQA to decide what needs to happen in terms of time-smear adjustment during the decoding.Speaking of, WMG is doing this with all those analog masters they're in the process of recording. I'll leave it to you folks to decide whether that does or doesn't imply that MQA transcoding is a major motivation for digitizing all those master tapes. In my opinion, it pretty clearly does imply that, but I know some folks are a bit cynical when it comes to all things MQA.
Jim
Edits: 11/01/16
> An ADC is still an ADC. The answer in the linked interview does not state
> there is anything special about the ADC function for MQA except 'low
> modulation noise', i.e. it should be a good ADC.
There are 2 strategies for designing an ADC with a very short impulse
response of the type desired by the MQA system. One is to use a true DSD
converter running at 128Fs or higher with a first-order low-pass
antialiasing filter set well above the desired passband. The other is to do
what Ayre has done in its QA-9 converter at 192kHz, where it uses a
moving-average low-pass filter, of the type described by Keith Howard at
the article linked below.
John Atkinson
Editor, Stereophile
Hi John,
I'll stick with my broad-brush 'an ADC is still an ADC' if only to back-up Jim's original statements and not to suggest that Isaac is in any way correct. Now, pretty much all (or just plain all?) ADCs are over-sampled types and the modulators are essentially similar, at least in my way of thinking. All highly-oversampled with a few bits of resolution. How those bit-streams are later decimated, with whatever resulting temporal response, is, to me, secondary.
As you mention DSD, I find it ironic that a recording format was developed to support 1-bit converters only for the converter industry to move away from 1-bit designs because they don't work that well.
When I see some of the arguments that have spun out of MQA related posts I am reminded of the New Yorker cartoon you told me about at the Newport Beach show in June!
Regards
13DoW
I thought this thing could raise the dead, or at least make a Toscanini / NBC Symphony Orchestra recording sound half decent ... now it's just these two things that put out what is desired by the MQA system ???
Better get those MQA samples examined for something else hiding in the origami ... seems to be scrambling the minds of the audio press.
;)
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