Features

Manufacturer's Comment

Editor: Thank you for the chance to respond.

In fig.3, the green/gray curves show the observed spectrum with no decoder. The noted small rise of noise in the treble is in fact a manifestation of the (noise-shaped) MQA signaling, rather than buried higher-frequency information. This signaling is at this level for wide compatibility and is completely removed by the decoder; the buried information from the higher octave is at a lower level.

The level at which MQA buries information from higher octaves is not predetermined; it's responsive to the content. However, the burying level is completely stationary throughout every song or work. In JA's recording of "Amazing Grace," MQA buries the top-octave information (as broadly white noise) below the 20-bit level in the majority of the audioband. This does not mean that the channel is limited to 20 bits—the DAC still receives a 24-bit signal. It simply means, in this case, that MQA's effective noise floor is more than 5 bits below the (minimum 15-bit) noise floor of the original signal—a very healthy margin, and on a par with the very best converters.

This can be seen in fig.1, which examines the end of the original WAV file, MQA (with and without decoding), and the underlying MQA channel noise in this recording (also with and without decoding). Also shown are reference levels for 16-, 18-, and 20-bit dither in a channel sampled at 88.2kHz (footnote 1).

In the graph, the noise-floor curves overlay for both MQA decoded and Original master. We can also see that the shaped HF noise introduced by the MQA encoder and "heard" without a decoder is removed by the decoder, at which point the noise falls from purple to brown.—J. Robert Stuart, MQA

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Footnote 1: The analysis uses 21.53Hz bins (=44,100/2048 and 88,200/4096), giving an offset of +13.33dB with respect to 1Hz.