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Seems to me MQA is a direct descendant of HDCD. Just using more bits.
Maybe a more sophisticated engine. (also HDCD was encoded IN a CD, Where MQA is working on download files with it encoded in them. But IMO it is still the same basic idea. (the coding was still being done on the fly)
HDCD never got off the ground due to licensing etc. Just not enough industry wide support.
I wonder if MQA is facing the same fate?
Also... IS MQA really a child of HDCD?
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My superficial understanding of both HDCD and MQA is that MQA may utilize a version of HDCD's hiding of extra information in the channel noise floor by disguising it as pseudo-noise. If I correctly recall (which, I may not), HDCD encoded control bits which instructed the DAC's interpolation filter to switch between different filter responses on-the-fly, depending on the moment to moment characteristics of the music content.As I understand it, MQA does not switch between different filter functions. It instead uses the the channel noise floor to hide ultrasonic information bandwidth by folding it down in to the channel as pseudo-noise. In that way, a channel bandwidth can be stored and transported as a file one quarter of it's original size and bandwidth. I believe that MQA utilizes this additional bandwidth to enable the employment of an soft slope, non-brickwall anti-alias filter at recording without violating Nyquist, and a similar filter at playback to minimze interpolation filter impulse response ringing. Not primarily for the purpose of capturing ultrasonic music content. Which maybe is why the ultrasonic band can be encoded at a low enough SNR to appear as noise without reducing the resolution of the audible content.
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Ken Newton
Edits: 01/12/17
These new compression / expansion schemes seem to be a modern digital twist on companding noise reduction aka Dobly DBX from the tape era. Or, I could be completely wrong. ;-)
Hi Abe,
Those systems were for the purpose of signal dynamic range compression / expansion.
What MQA is on to is signal bandwidth expansion. As far as I can tell, primarily for the purpose of easing the time domain consequences of utilizing the sharp band-limiting filters that would otherwise be required by the sampling theorem. Meridian's key performance objective with MQA appearing, to me, as the minimization of signal time domain distortion. The bandwidth compression aspect of MQA appears to then be a way of wrapping a wide bandwidth signal within a narrow channel for compact storage, transport, and also for compatibility with existing media.
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Ken Newton
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