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Re: [ARSCLIST] 1937 shellac test pressing outperforms audio CD
Eric Jacobs wrote:
I apologize in advance for cross posting.Likewise excuse the cross-posting of my response.
I couldn't help sharing this - I am regularly measuring 27.2 kHz
harmonics and occasionally as high as 43.6 kHz harmonics (violin)
from a series of 1937 RCA Victor test pressings - nearly 72 years
old. I'm pretty fastidious about accurate cartridge loading, so I
don't think we're seeing ringing of the transducer.
But they could be harmonic ringing of the mechanics of the cutter
head--the other mechanical device in the chain. You have to consider
the source feeding the recording head--the microphones and amplifiers.
If they were using RCA 44-BX Ribbon Velocity microphones, their top end
is 13K to maybe 16K depending on the condition of the ribbon. There
also are limitations of the impedance matching transformer in the base
of the microphone. Then what are the top ends of the RCA pre-amps and
amps in use in 1937? I would think they would be rolling off by at
least 20K if not lower. We probably can't be sure even if we check the
spec sheets because I doubt they were measuring any higher.
While you are at it, I'd like to see what you measusre on Western
Electrtic Wide Range Vertical Recordings such as used by World,
Associated, and Muzak. They claimed 13K around 1933-34. I have a
matched pair of World test pressings of the same broadcast on a lateral
and a vertical, and while the lateral is great, the vertical IS better!
I mentioned yesterday on the 78-L a 1932 Victor of Astaire with George
Hall's orch on the Buddha CD "Time Capsule" which has highs that are
unbelievable. Vince Giordano produced it. I think this side was done
off a vinyl test from the Victor Vintage series era, or maybe even a
metal. Victor and other companies routinely polished their masters or
stampers with jeweler's rouge which probably removed the rough edges of
the sound wave -- namely the high frequencies. George Brock-Nannestad
discovered a document at EMI that discussed Victor running a knurling
tool thru the grooves to likewise smooth them out. Victor subjected
tests to wear tests to make sure the records wouldn't wear out
prematurely. Rough grooves wore out faster. GOOD RECORDINGS wore out
faster!! There is evidence that Victor "dumbed down" their recordings,
so it is important that you have access to those test pressings which
might not have been compromised. But maybe some of the things Victor
was polishing off were cutter-head transient ringings.
Mike Biel mbiel@xxxxxxxxx
> Never mind that we've invested nearly $60k in our analog disc
playback and digitization system, pushing the limits of what is
possible, but I was astounded by the recording quality and performance
of these particular discs that long preceeded modern formats like
magnetic tape and LP, let alone CD.
> For those who have the ability to measure this sort of thing,
I can email 1-second and 2-second samples (24/96 WAVE files).
For those that do not have access to a high-resolution spectrogram, I
can send jpegs taken from ours. The WAVE files altogether are
2.3 MB - not especially large - but you should still make sure that your
email software and internet connection can handle email
of this size.
The Audio Archive, Inc.