In article ,
(Don Pearce) wrote:

On Tue, 15 May 2007 17:02:56 GMT, (Don Pearce)
wrote:

On Tue, 15 May 2007 16:52:53 GMT, John Byrns
wrote:

In article . com,
Peter Wieck wrote:

On May 14, 10:21 am, John Byrns wrote:

No, you have that exactly backwards, the RIAA recording curve reduces
the groove amplitude at high frequencies, requiring a complimentary high
frequency boost in playback, which increases the effects of surface
noise.

From: RIAA Equalization Curve for Phonograph Records
By: Don Hoglund

http://www.graniteaudio.com/page5.html

Peter, that URL is dead, it doesn't work! That aside, it isn't clear
what the point of your post is? Are you trying to say that my statement
which you have quote above is wrong? If that is so just spit it out and
tell me exactly what I said that is factually wrong?

However, because the cutter head's movements translate the amplitude
swings of the original signal into velocity -

This is not true, at least historically. IIRC in the early days of
electrical recording the cutters were constant amplitude below the
"turnover" frequency and constant amplitude above the "turnover"
frequency. This response was a result of carefully damped resonances
which were inherent in the design of the cutter head. Early stereo disc
cutters had a response which looked like a mountain peak with a
resonance in the middle of the audio band. Aassuming these curves were
velocity referenced, this would again imply constant amplitude operation
in the area to the left of the mountain peak. I have no knowledge of
the response of contemporary disc cutters, perhaps Iain could chime in
here, but I would be very surprised if their response was anything near
the perfect velocity response you assume. As a result of all this the
electrical equalizers used in disc cutting produce a curve that looks
nothing like the RIAA recording curve commonly presented on web sites,
as they must compensate for the mechanical effects of the cutter head.

You have also failed to consider the old crystal cutter heads that were
used in home disc cutting setups, as well as in some semipro equipment.
Even an ideal cutter head of this type would not produce a constant
velocity recording from a constant amplitude input signal.

the rate at which the
stylus moves during its swings - low-frequency signals would be
recorded with a much larger swing than high-frequency signals of the
same original amplitude. So, the low frequency grooves would be much
wider than the grooves on an equalized disk.

This is only because you have chosen to take a velocity centric
perspective, if you took the more natural groove amplitude view, you
would see that the low frequency grooves would be no wider than high
frequency grooves, and that in fact the amplitude of the high frequency
grooves would have to be reduced, as they are in discs cut to the RIAA
curve by some 12 dB, in order to prevent excessive groove velocity from
occurring at high frequencies. Grooves cut with excessive velocity are
difficult for playback pickups to track without creating excessive
distortion.

The high frequency amplitude cut incorporated into the RIAA recording
curve necessitates that a complimentary high frequency boost be
incorporated into the playback curve. This high frequency boost during
playback decreases the signal to noise ratio of the LP by emphasizing
the high frequency surface noise by some 12 dB.

Peter, don't be one of the sheep, take a moment and think for yourself
for once. If you can't do that at least make it clear what the point of
your post was and tell me specifically what part of my previous post it
is that you take issue with?

John, are you still insisting that RIAA playback requires high
frequency boost? It doesn't. An RIAA phono preamp has a feedback
mechanism that provides high frequency cut. I have designed several
myself, and studied the circuits and operation of many. Had I (and
every other designer on the planet) been getting it wrong all the
time, our systems would be muffled and entirely without top. They are
not; they play back just fine, and certainly for my own, when I play a
white noise track on a test disc (recorded with standard pre-emphasis
before you say anything), I recover noise which is flat within about
1dB from 30Hz to 20kHz.

*Please* go and do some reading so you can back away gracefully from
this ridiculous position you are placing yourself in.

John, my apologies. I have only just noticed that you are posting from
rec.audio.tubes as your prime group. Ignore everything I wrote above -
you are right and I am wrong. Just as Alice found when she stepped
through the mirror into looking glass land, everything there works
backwards from the real world.

Don, I don't understand what the prime group I am posting from has to do
with this issue and your sudden understanding? Could you please explain?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/