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MQA CDs

Hi Sue,

The easiest way to understand what happens with MQA CDs is to look at the block diagram taken from the MQA patent and posted on the Benchmark website (link below).

The first step is to start with a 96/24 digital audio file. This is sent to a 96kHz noise shaper that outputs only 17 bits. Next comes a frequency splitter that separates the baseband (0 - 24kHz) from the double-rate information (24kHz - 48kHz). Since there *still* ain't no such thing as a free lunch, to preserve the double rate information requires that some of the baseband information be discarded, so that everything will fit in the container. (In other words, you can't fit a gallon of whiskey in a pint jar.)

When the container is a 24-bit FLAC file as used with computer audio (streaming and downloads), then 17 bits of baseband information is retained (resulting in an audible loss of resolution in at least some tracks - I have pointed out The Doors "Riders on the Storm" "whisper overdub" is difficult to make out on the MQA version and this was confirmed by a Stereophile reader in the online comments of the Mytek Manhattan.

Then the relatively low dynamic range of ultrasonic musical information is stuffed into the lower 4 bits of an MQA 24-bit FLAC file. But the container on a CD is only 16 bits! Now what?

It turns out (and is easily seen in the block diagrams, that the original 24-bit baseband resolution is reduced to only 13 bits (!) and the ultrasonic information in the double rate band now uses *lossy* compression (similar to MP3) to fit it in the bottom 3 bits of a 16-bit CD container. (Some who have reverse engineered MQA in 24-bit FLAC containers say that at most 1 bit represent the double-band information for CD, as the 2 LSBs contains a signal telling the "renderer" which digital filter to use.)

I personally don't get it. When CD was first introduced and everybody said it sounded horrible, the common assumption was that the problem was too few bits (resolution) and too low of a sampling rate. That's why HDCD was developed - to increase the resolution of a standard CD. (It turns out that it only increased it by 1 bit rather than the claimed 4 bits, but that's another story that can be read about at: https://www.audioasylum.com/audio/digital/messages/18/184385.html

It's hard for me to fathom that 13 bits of resolution in the baseband is considered "high-resolution" by the Japanese majors: "Consumer audio products that came with the "Hi-Res AUDIO" logo indicate that the product meet the specification required for a high resolution audio product, as defined by Japan Electronics and Information Technology Industries Association (JEITA)." But there you go - Orwellian "newspeak" at its best.

Hope this helps,
Charles Hansen

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