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ARSCLIST  June 2009

ARSCLIST June 2009

Subject:

Re: (Fwd) [ARSCLIST] Fwd: Recording Speed

From:

Michael Biel <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Mon, 22 Jun 2009 11:23:26 -0700

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (180 lines)

I understand what George is saying partially because I've seen him do it
and I am lucky enough to have one of his calibration discs.  In case
Doug and others still do not understand it, Doug's snip cut out the
important info and left in material that has no meaning without the
snipped part.  


In 1982 George commissioned a 7-inch pressing made of a 450 Hz. tone cut
at 45.0 RPM.  That disc can be played at any RPM and a frequency counter
will show a reading that is 10 times that RPM. (Play it at 73.7 RPM and
it shows 737.0 Hz.  78.26 shows 782.6 Hz. Etc.) If you have a frequency
counter handy, you can find what rotational speed you are using.  BUT,
if you include a few seconds of that calibration disc played on the same
turntable at the time of your transfer of the record you are working on,
then later on that frequency can be read with a counter and at any time
you can establish the rotational speed you used. It's like an audible
strobe disc that has the unique ability to be recorded, and it is as
accurate as your frequency counter is.  Sure, you could use a normal
test disc of, say, a 1000 Hz. tone, but George's disc is more directly
readable without using math to have to determine percentage of 1000 Hz.
whatever tone you used.

Mike Biel  [log in to unmask]  


 

-------- Original Message --------
Subject: Re: [ARSCLIST] (Fwd) [ARSCLIST] Fwd: Recording Speed
From: George Brock-Nannestad <[log in to unmask]>
Date: Sat, June 20, 2009 5:43 am
To: [log in to unmask]

From: Patent Tactics, George Brock-Nannestad

Hello,

Doug Pomeroy wrote (I have changed the sentence order to facilitate 
communication) :

> Forgive me, but I do not understand this. Could you explain it in 
> other words?
> Maybe it's simpler than I think.

> >
> > From: Patent Tactics, George Brock-Nannestad
> >
> 
> <SNIP>
> 
> > In use of the tape
> > as a secondary master, the content could be de-chipmunked by 
> > changing the
> > speed of the tape recorder, and the tape rewound to the calibration 
> > track,
> > which was measured by the counter and would give the rpm of the 
> > original
> > record at the de-chipmunked speed. This way, the actual transfer 
> > rpm is
> > completely immaterial and may be chosen for good tracking--we can 
> > still get
> > at the rpm, just as if we had access to the original record.
> 

----- I shall describe it as a witness would, who observed what I am
doing. 
However, it is fairly long, and those who detest long postings had
better 
leave now.

On the table we have a turntable with pickup, a record to be
transferred, a 
tape recorder (nowadays it would be some digital stuff), and my speed 
calibration disc SC. This disc has been prepared by cementing a
straightened-
out paper clip to the label, so that a piece of wire sticks up at the
center 
of the SC. This permits you to lift the SC and place it anywhere, even
on a 
rotating turntable.

The record to be transferred is placed on the turntable and the SC is
put on 
top of it - use either the edges or the wire. Start the turntable and
the 
tape recorder and let the pickup play the SC track - 5 seconds is
plenty. 
Lift off the pickup, lift off the rotating SC by means of the wire,
place the 
pickup on the rotating record to be transferred; a smooth operation that
does 
not take long. All the time the turntable rotates and the tape runs.
When the 
record has finished you can do two things: either just switch everything
off 
or replace the SC and play another 5 seconds at the end. When the tape
stops 
it contains the following: ca. 5 seconds of calibration signal followed
by 
some noises, followed by the transfer of the record (and then possibly 
another 5 seconds of SC for good measure). 

Now, the calibration signal on the tape is made to express in Hertz 10
times 
the rpm of the record - how this is obtained will be told below. This
means 
that if you measure 800 Hz as the frequency of the calibration signal,
then 
the turntable made 80 rpm at the transfer. If you fiddle with the speed
of 
the tape when playing the transfer until you get a reasonable sound (in
tune 
with something, for instance, or in a b key for a brass band), then you
have 
interpreted the transfer. If you want to know what rpm the turntable
should 
have had to provide this reasonable sound from the original record, you
go 
back to the calibration part of the tape and reproduce that with no
change of 
speed, i.e. with the speed you fiddled your way to for the transfer, if
you 
will get for instance 720 Hz, it would correspond to 72 rpm. Based on
the 
tape copy you will in other words be able to specify a speed for a
record you 
do not necessarily hold in your hand.

This means that you can do your transfer at e.g. 33 1/3 rpm, which
improves 
tracking and is a standard speed obtainable from almost all modern 
turntables. On reproduction of the tape you increase the speed of the
tape 
until your SC part of the transfer provides, say, 780 Hz, which will
then 
make the sound of the transferred record sound as if it was reproduced
at 78 
rpm. There are some de-emphasis issues that we do not need to go into
here, 
because they have nothing to do with pitching the record. The whole idea
is 
that you have the same change of pitch in the SC signal as you have in
the 
record signal, because they were transferred under the same speed
conditions.

By making the SC signal having the special relationship to rpm we avoid 
calculations that one would otherwise have to make. It is a signal that
will 
provide 600 Hz at 60 rpm, which is 1 revolution per second. This means
that 
the groove has to have 600 cycles on one revolution - it could be a
locked 
groove! When the turntable speed is increased, the frequency increases
in 
proportion. I did toy with the idea of having a special nickel turntable

platter (in effect a mother) made like a turntable mat with such a
locked 
groove at a radius that was outside any record that one might want to 
transfer. Instead of placing and lifting off a calibration record, one
would 
simply play the locked groove before (and after) playing the record.
Another 
way would be to have a timebase signal derived from the turntable
platter and 
record that on the second track of a stereo tape (or a third track when 
recording digitally). I have not myself used anything but my own Speed 
Calibrating Record SC-1. And nickel is not a good turntable mat
material, 
because good MC pickups are seriously attracted downwards to this
material.

I hope that this has clarified matters.

Kind regards,


George

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