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RE: OK, now we are on the same page - it is aliasing *and* it is a bug.

Charles, I lack your experience-based perspective, so I guess to me it doesn't seem that odd. I go back to (one of) the patent application(s) and see this language:

>>Preferrably, the downsampler comprises decimation filter specified at the first sample rate, wherein the asymmetric component of the response of the decimation filter is characterized by an attenuation of at least 32dB at frequencies that would alias to the 0-7kHz range.

The range 0-7kHz is where the ear is most sensitive. The amount of attenuation required varies greatly according to the spectrum to be encoded in the vicinity of its Nyquist frequency, and may [sic] signals will require more than 32dB of attenuation.<<

For CD-res, 7kHz is Nyquist - 15kHz. So what's the attenuation of that MQA filter JA measured at Nyquist + 15kHz = 37.1kHz? It looks to be down about 55dB, give or take, which even with this slow roll-off easily meets that spec. Looking at the Beyonce track--comparing 7kHz with 37kHz--just eyeballing it this time, not going back to the Audition file--the levels seem to be about -70dB at 7kHz and about -120dB at 37kHz--so, again, aliasing spec easily met--even with this very gentle filter.

MQA has been quite explicit about the desire to trade aliasing for time resolution. They appear to be doing just what they said they would do--so I don't see why you'd call it a bug. Surely they'd call it a feature.

One thing I don't understand is why you say they're using a double-rate filter. The filter shown in JA's Fig. 6 accurately describes the data, is flat not quite to the 44.1 Nyquist frequency (that is, about 22kHz). It describes what's happening but it would never work for 96kHz data.

Otherwise, we seem to have converged on an interpretation.

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  Michael Percy Audio  

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