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RE: To be precise...

>> Any thoughts on how the QX-5's decoding of HDCD compares with
dbpoweramp's rips of HDCD CDs, Charley? <<

Good question, but I don't know the answer.

HDCD decoding has been available in both dBpoweramp and Foobar for many years, and for many years there have been various versions of the HDCD algorithm floating around the internet. Looking at the source code for the two versions I could find, I am clear that the most important HDCD feature (expansion curve for the "Peak Extend" function) is slightly off in both. Apparently the values for the inverse-gain curve were estimated by eyeball from the graphs published in the AES paper in one version. While the other version was alleged to have come from a decompilation of the code used in Microsoft's Windows Media Player (MS purchased Pacific Microsonics in September 2000), it also contained obvious errors in the inverse-gain curve.

I'm far more OCD than to use inaccurate values and instead took the effort to learn the exact 16-bit values for every single point in the curve (which compresses the top 9dB of signal into only 3dB on the disc). The end result is that I am confident that Ayre's implementation is bit-accurate with the original, while the other versions I've seen are not. I am unsure if the code used in dBpoweramp is based on the slightly inaccurate code circulating on the internet or if they also took the trouble to get it exact. I am also completely unsure of the audibility of the errors in inaccurate versions.


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