Thread: MQA Discussion
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Old 05-25-2017, 05:56 PM
James Tanner - Bryston James Tanner - Bryston is offline
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There's no free lunch

Posted by Charles Hansen (M) on May 22, 2017 at 16:57:53
In Reply to: MQA ... why bother? ... why not just use least significant bits truncation? posted by bjh on May 22, 2017 at 12:34:09:

While it is true that there is no such thing as a free lunch, the converse also holds true. While MQA discards the lower bits in the baseband of a true high-res (eg, 192/24 LPCM) source file, they are replaced with losslessly compressed bits from the dual-rate band and lossy compressed bits from the quad-rate band. Both of these "foldings" represent data that is correlated with the music. Therefore even though an MQA file is a lossy representation of the original high-res file (as information theory dictates), it does contain more information than would be by simply truncating the bits of a single-rate file. In other words, a 192/24 file fully hardware decoded by MQA will have a maximum resolution of ~192/17.

If one believes that bit depth is the most important parameter, this would not be much of an improvement over a standard Redbook (44/16) file. On the other hand if one believes that the sampling rate is more important (as do I, as it allows for much gentler, less destructive filters), then there is a benefit. However why not have your cake and eat it too? At the Munich show Qobuz announced a third tier (above Redbook FLAC Sublime) called Sublime+ that allows for full high-res streaming of files up to 192/24. An interesting note is that this costs more money. The implications is that those who set the pricing (largely the record labels and copyright holders) apparently value true high-res files more than MQA files, as the price for MQA files is the same as the price for Redbook files. Possibly a case of getting what you pay for.

MQA's argument is that the bits that are discarded (and replaced by other correlated bits) in order to reduce the file size are inaudible. That is precisely the same claim that was made regarding MP3 - sonically indistinguishable. My most recent technical analysis (with minor corrections from previous posts being noted in the paragraph beginning with "NB") is in this post:

https://www.audioasylum.com/audio/di...18/184101.html

As always my posts reflect strictly my own opinion and not that of my employer, family, or book-club members.
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