Has anyone read the article "Dirty Digital" by Noel Keywood in July's
"Hi-Fi World"? I picked up a copy for some amusement during a journey
yesterday and was stunned by the article's technical incompetence.

Keywood says of CD that "dynamic range is limited to 85 dB or so by
dither noise" (incorrect - it's actually about 93.3 dB IIRC for 2 LSB p-p
of TPDF dither). Then he complains, disingenuously, about the "dirty
distortion" of quantization on CD (he calls it "digital distortion"),
misunderstanding the fact that it just isn't present when you use dither.

He even misunderstands the issue of correlation between signal and
quantization error, calling them uncorrelated whereas they actually
are correlated and dither's job is to de-correlate the two.

He mixes up distortion and noise inconsistently under the single term
"distortion" sometime meaning noise, sometimes distortion and sometimes
noise+distortion.

Here's another example. He says CD distortion [sic.] is 10% at -80 dB
(dBFS he means, I assume) and later says that "LP is benign and also
produces ten times less distortion than CD at low levels (0.1% to 1%)".
In fact at the comparable low level on LP of -80 dB (WRT 0 dB = 5 cm/s,
I will assume) the LP noise floor is actually above the signal and the
LP's distortion in Keywood's terms is above 100%.

He says of the music business that it "now tries to keep music levels
well above the unacceptably high distortion floor of CD that we illustrate
here". Well, that's a new explanation for the "loudness war".

I think Keywood should have a good look at Jim Lesurf's "Good Resolutions"
article at http://www.audiomisc.co.uk/HFN/goodr...ons/page1.html
(in particular figure 5 on page 2 will show him a realistic comparison
of dynamic range of CD versus LP). Also Jim's article "In a Dither"
at http://www.audiomisc.co.uk/inadither/Page1.html would show him where
his misunderstanding about dither lies.

Keywood starts out with "This isn't a hatchet job of the poor little
silver Frisbee" and then proceeds to try just that. In fact through
his clear technical misunderstandings the only thing that suffers a
"hatchet job" is Keywood's own reputation for competence.


--
John Phillips