LISTSERV mailing list manager LISTSERV 16.0

Help for ARSCLIST Archives


ARSCLIST Archives

ARSCLIST Archives


[email protected]


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Monospaced Font

LISTSERV Archives

LISTSERV Archives

ARSCLIST Home

ARSCLIST Home

ARSCLIST  November 2015

ARSCLIST November 2015

Subject:

Re: 78rpm replay speeds & pitch

From:

George Brock-Nannestad <[log in to unmask]>

Reply-To:

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

Date:

Sat, 28 Nov 2015 02:00:46 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (202 lines)

From: Patent Tactics, George Brock-Nannestad


Hello,

mains hum is a good indicator under two circumstances: 1) that the mains
frequency is known for the duration of the recording, and 2) that the motor
driving the turntable is not a synchronous motor. For 78s, which are under
discussion here, there is a fixed relationship: for 50 Hz drive the turntable
runs at 77.92 rpm and for 60 Hz drive it runs at 78.26 rpm. But as the power
frequency drops, so does the rpm, so the hum inscribed will always become the
standardised hum if you run the turntable at 77.92 or 78.26 as the case may
be. It is not an independent reference with a synchronous motor.

Most of Argentina's electrical power before the formation of the national
power grid in 1960 was hydroelectric, which is known to have large variations
because the regulation of a water valve is slow. And as there was no national
grid to form a flywheel, variations could be large. Obviously, on a 24hour
basis (integration over 24 hours) the average was the intended with a very
high precision. Some places had direct current!

The alternative was to use a universal motor with a centrifugal governor, and
they could be precise, certainly on a 5-minute basis.

Eric Jacob's calculations are not relevant in the case of a centrifugal
governor, because using torque as his variable, he is in effect using a
constant current equivalent. But the relevant variable is constant rotational
speed ("voltage"), and that is precisely what the centrifugal governor
supplies. There needs to be sufficient power available (and a bucketful of
nuts as used on the gravitational motors will supply that), and any power in
excess of that needed to maintain the speed the motor is adjusted to is
absorbed in the centrifugal governor. This means that if the turntable is
acting as a variable brake, such as when cutting, then the centrifugal
governor eases up to the necessary degree. It is is fast-reacting because the
centrifugal governor is fast-rotating due to gearing.

They are also not relevant in connection with a synchronous motor drive,
because either the braking torque is too high, and the motor stops, or it is
not, and it runs at constant speed. The variation can be in the phase, a very
small angular displacement, because there will be some shifting of the poles
on the rotor with respect to the stator that carries the coils.

The conscecutive recording from the outside to the center on the first and
from the center to the rim on the second, and repeating that sequence was
essentially a broadcast technique. No commercial record sets were issued like
that. And the reason was not variations in speed but variations in sound
quality due to inner-groove distortion. The change-over was less noticeable
-- on that we agree!

Finally, as to clicks derived from a radial scratch from the center and
outwards: as the rpm is constant it means that a click comes once per
revolution on the dot, provided the rpm is absolutely constant. But also
scratches shaped like an Archimedes spiral will give equally timed clicks, so
a listener to a copy may be confused.

Best wishes,


George


Eric Jacobs wrote:

> For those who donıt mind a physics/mathematical representation of
> whatıs going onS
>
> The torque of the turntable motor is constant.
>
>
> When cutting...
>
> The torque due to stylus friction while cutting a groove varies with
> radius:
>
> Stylus Torque = Radius X Stylus Cutting Force
> Radius outer groove > Radius inner groove
> Stylus Torque (outer grooves) > Stylus Torque (inner grooves)
>
>
> When playing...
>
> Stylus Cutting Force > Stylus Playback Force
>
>
> When cutting...
>
> Net Torque = Turntable Motor Torque - Stylus Torque
>
> Net Torque (outer grooves) < Net Torque (inner grooves)
>
> RPM (outer grooves) < RPM (inner grooves)
>
> Because there is more net torque when cutting the inner grooves, the
> turntable spins a bit faster when cutting the inner grooves. Or you
> can think of it the other way - that the turntable spins slower when
> cutting the outer grooves because there is less net torque.
>
>
>
> When playing...
>
> Net Torque is more constant because the Stylus Torque during
> playback is so much smaller than during cutting.
>
> Net Torque = Turntable Motor Torque - Stylus Torque (very small)
>
> Net Torque (outer grooves) ~= Net Torque (inner grooves)
>
>
> RPM (outer grooves) ~= RPM (inner grooves)
>
>
> Pitch variation is a function of playback speed variation
>
> IMPORTANT: When playback speed is faster than the recording speed,
> the pitch is higher, and vice versa. This is the essence of why
> there is pitch variation.
>
>
> Recall from above:
>
> When cutting: RPM (outer grooves) < RPM (inner grooves)
> When playing: RPM (outer grooves) ~= RPM (inner grooves)
>
> and therefore
>
> RPM cutting (outer grooves) < RPM playback (outer grooves)
>
>
>
> The playback RPM on the outer grooves is faster than the original
> cutting speed. Therefore the outer groove pitch is higher than the
> pitch on the inner grooves (or vice versa, the pitch on the inner
> grooves is lower than the outer grooves).
>
>
> To account for this variation in speed during recording, the
> recording engineer would cut the first disc in a series starting
> with the outer groove. The second disc in a series would start
> on the inner groove, so that the speeds would more closely match
> between the first and second discs. Inner and outer groove start
> would continue to alternate during the recording session.
>
>
> Hopefully this somewhat long-winded mathematical explanation is
> helpful.
>
> ~ Eric
>
> Eric Jacobs, Principal
> The Audio Archive
> 1325 Howard Ave, #906, Burlingame, CA 94010
> Tel: 408-221-2128 | [log in to unmask]
> http://www.theaudioarchive.com/
>
>
>
>
> On 11/27/15, 9:09 AM, "Association for Recorded Sound Discussion List on
> behalf of DAVID BURNHAM" <[log in to unmask] on behalf of
> [log in to unmask]> wrote:
>
> >I think the obvious answer to your second question is insufficient torque
> >on the recording turntable. This happened on many recorded sides, one
> >example that comes to mind is the Weingartner "Les Preludes" by Liszt.
> >The cutting stylus puts considerable drag on the turntable and that drag
> >increases towards the centre of the disc, dragging the speed down. If
> >the recording turntable motor is not VERY strong and is unable to
> >maintain the corrrect speed throughout the cut, the resulting slower
> >speed towards the end of the side gradually raises the pitch on playback.
> > With modern digital workstations, this error is easy to fix, but back in
> >the days of reel to reel tape, trying to rejoin the sides on the
> >aforementioned "Les Preludes" was a nightmare.
> >db
> >
> >
> > On Friday, November 27, 2015 11:48 AM, Andrew Hallifax
> ><[log in to unmask]> wrote:
> >
> >
> > Thanks for your contribution Jolyon. I am in fact following all such
> >advice
> >and practices as you describe. We're working on the presumption that
> >standard pitch seems to have been adopted in Argentina sometime during
> the
> >late 30s. Regardless of how true that is, our presumption is supported by
> >most other discs in the series produced during the 1950's which render
> >more
> >or less reliably A442ish at nominal 78rpm.
> >However, my question to the list was aimed not so much at resolving the
> >pitching/speed conundrum per se, but in the hope of discovering whether
> >anyone might offer an insight into why speeds were inconsistent across
> the
> >two sides of discs recorded on the same day and bearing adjacent
> matrices,
> >and also, why or how certain recordings of this period change pitch
> during
> >the side.
> >
> >
> >

Top of Message | Previous Page | Permalink

Advanced Options


Options

Log In

Log In

Get Password

Get Password


Search Archives

Search Archives


Subscribe or Unsubscribe

Subscribe or Unsubscribe


Archives

March 2024
February 2024
January 2024
December 2023
November 2023
October 2023
September 2023
August 2023
July 2023
June 2023
May 2023
April 2023
March 2023
February 2023
January 2023
December 2022
November 2022
October 2022
September 2022
August 2022
July 2022
June 2022
May 2022
April 2022
March 2022
February 2022
January 2022
December 2021
November 2021
October 2021
September 2021
August 2021
July 2021
June 2021
May 2021
April 2021
March 2021
February 2021
January 2021
December 2020
November 2020
October 2020
September 2020
August 2020
July 2020
June 2020
May 2020
April 2020
March 2020
February 2020
January 2020
December 2019
November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
November 2010
October 2010
September 2010
August 2010
July 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
March 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
July 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
August 2007
July 2007
June 2007
May 2007
April 2007
March 2007
February 2007
January 2007
December 2006
November 2006
October 2006
September 2006
August 2006
July 2006
June 2006
May 2006
April 2006
March 2006
February 2006
January 2006
December 2005
November 2005
October 2005
September 2005
August 2005
July 2005
June 2005
May 2005
April 2005
March 2005
February 2005
January 2005
December 2004
November 2004
October 2004
September 2004
August 2004
July 2004
June 2004
May 2004
April 2004
March 2004
February 2004
January 2004
December 2003
November 2003
October 2003
September 2003
August 2003
July 2003
June 2003
May 2003
April 2003
March 2003
February 2003
January 2003

ATOM RSS1 RSS2



LISTSERV.LOC.GOV

CataList Email List Search Powered by the LISTSERV Email List Manager