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From: Patent Tactics, George Brock-Nannestad

Hello all,

I am beginning to feel old. The creation of standards for recording and 
reproduction may have been a lovely ideal, but in practice if floundered, and 
this was realized by the standardization bodies themselves. I wrote about 
this in 2001:

Brock-Nannestad, George: "Pre- and De-Emphasis - A 
Forgotten Necessity", AES Preprint No. 5360, 110th Convention 2001 May 12-15,
Amsterdam.
	(an historical overview of standard compensations introduced in the 
recording-reproducing chain and the arguments used over time, ending with 
total resignation on the part of a standards body), and I quote the passage I 
am referring to:

"Reproducing characteristic tolerances -- No tolerances are specified since 
commercial reproducers normally contain a tone control which may vary their 
frequency characteristic over a wide range" (IEC 1958)

This was after the following comment from the AES in 1951 concerning the 
specification of the AES Standard Playback Curve:

"The decision to specify a standard playback response characteristic instead 
of a recording characteristic was deliberate on the part of the Standards 
Committee. This course was chosen because of the impossible task of achieving 
a universal recorded characteristic compatible with all individual recording 
conditions and systems"

The list of my publications that the above is taken from was posted on 
ARSCLIST on 26 July 2004.

Recently, in discussions in the IASA Technical Committee over the upcoming 
revision of TC 04 I stressed that there were quite broad tolerances in the 
standards (also visible in Richard Hess' reproduction of the RIAA standards), 
except at 1000 Hz. So in the IASA TC discussion I made the curve showing the 
de-emphasis fat corresponding to the + and - tolerances, and you are now - 
obviously - all over the place but - equally obviously - still within the 
requirements of the standard. In other words, any curve that can be "hidden" 
below the fat line is within the tolerances.

Furthermore, the blanket statement that the phase response follows 
causatively from the amplitude response is only true for the class of minimum-
phase networks. This means that if the RIAA is made by passive components it 
may be different from when it is generated as part of a feedback loop. In the 
digital domain you are able to ensure that the transfer function you specify 
is the correct one (well, the one you aim for!), within 0.001 dB (or better, 
try to convert 24 bit into percentage precision and be ashamed!), and 
furthermore that both stereo channels are absolutely equal and tracking. But 
is the output from your pickup up to the challenge of interchannel 
differences of 0.001 dB over the frequency range of interest? I think not! 
Not for a mechanical pickup. And my pet peeve: 24 bits resolution. The bits 
are there, they can be counted, but the step sizes corresponding to the last 
5 binary digits are not the same all the time. For this to occur you need 
analog stability, complete enclosure in an oven, after having burnt-in the 
various components. Agilent does provide this - at a price and at a sample 
rate of 1 Hz.

Equally in IASA TC work I have recommended the following book as a reference. 
It is probably the last ever book to be written about analog circuitry for 
phono pre-amplifiers. It comes at a price, but that should not frighten 
professionals:

Burkhard Vogel:
'The Sound of Silence. Lowest-Noise RIAA Phono-Amps: Designer's Guide'
Springer-Verlag Berlin 2008
ISBN 978-3-540-76883-8
e-ISBN 978-3-540-76884-5

352 pages:

Theory, including noise basics 143pp.
Best practice, including MM, MC cartridges, RIAA Networks 127pp.
Noise measurement system (better than the object measured!) 21 pp.
The RIAA Phono-Amp Engine 22pp.

Best wishes,


George