LISTSERV mailing list manager LISTSERV 16.0

Help for ARSCLIST Archives


ARSCLIST Archives

ARSCLIST Archives


ARSCLIST@LISTSERV.LOC.GOV


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

ARSCLIST Home

ARSCLIST Home

ARSCLIST  November 2015

ARSCLIST November 2015

Subject:

Re: 78rpm replay speeds & pitch

From:

Eric Jacobs <[log in to unmask]>

Reply-To:

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

Date:

Fri, 27 Nov 2015 17:08:49 -0800

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (250 lines)

Hi Malcolm,

The formula for a radial scratch/break is simply

    Time between pops = 60/RPM

The time between pops will not vary between outer and inner grooves
if the scratch or crack is “radial” (i.e. perpendicular to the
grooves).

In your example, 1 second between pops means 60 RPM.  And 1 second
between pops at the outer groove will still be 1 second between pops
at the inner grooves.

If the scratch/break is not orthogonal (not perpendicular to the
grooves), then the time between pops will vary depending upon the
angle of the scratch/break.

Of course, the formula has additional terms if the scratch/break
crosses a groove at an angle.  But you’ll see that the effect of
angle and pitch are fairly small.

The formula would look something like:

    Time between pops =
    60*pi*D / (RPM * (pi*D + 1/(pitch/tangent(angle))))

Where

    pi = 3.141596
    D = groove diameter (inch)
    angle = measured in degrees from orthogonal
    pitch = grooves per inch
    RPM = rotations per minute

Plugging this into a spreadsheet for 4.5-inch from the center
(D = 9 inches) and 120 pitch at 60 RPM (1 sec between pops)
and the angle of the scratch at 20 degrees…

    Time between pops = 0.99989 (D = 9 inches, angle = 20 deg)
    Time between pops = 0.99981 (D = 5 inches, angle = 20 deg)
    Difference = 0.00008 sec

Clearly, the variation in periodicity due to pitch, groove
diameter, and scratch angle is quite small (0.01 milliseconds)
and a second-order effect.

As the scratch gets closer to being tangent to the groove:

    Time between pops = 0.99890 (D = 9 inches, angle = 75 deg)
    Time between pops = 0.99802 (D = 5 inches, angle = 75 deg)
    Difference = 0.00088 sec


In theory, being able to identify the periodicity in noise and
using that to automate impulse noise reduction, seems helpful.
But it also assumes that the scratch is uniform in the way it
damages each groove (uniform depth and width). And the analysis
needed to distinguish impulse noise from percussion impulses
may not be practical. Asking someone to input scratch location
and angle is also not particularly practical either.

So, for all intents and purposes:

    Time between pops = 60/RPM

This, of course, assumes a CRV (Constant Rotational Velocity =
constant RPM) disc, which is the majority of analog recordings
on disc media. However, to make things exciting, there are CLV
(Constant Linear Velocity) recordings that were used by Gray
Audograph dictation discs.  In that case, these formulas won’t
work because the RPM varies with the groove diameter.  Gray
Audograph is one of our specialties for transfer work.


~ Eric


On 11/27/15, 12:56 PM, "Association for Recorded Sound Discussion List on
behalf of Malcolm" <[log in to unmask] on behalf of
[log in to unmask]> wrote:

>Hi Eric -
>
>Nice info, thanks. Good to know. Now, how about a mathematical formula
>that will tell one, if there is a linear scratch or a break that goes
>straight from record edge to center hole, exactly when the pop will
>sound from revolution to revolution along the groove.
>For instance (and I am just picking numbers out of the air by way of
>supposition) if it takes 1 second between two pops at the outer edge of
>the record, say 4.5" from the center, how long will it take between pops
>at 2.5" from the center? And how much less time will elapse per
>revolution at, say, a 120 groove pitch? It will obviously be a
>decreasing number the closer to the center of the disc one goes. There's
>got to be a (simple) formula!
>I have long thought that using an algorithm to determine where the pops
>will fall would be of great help in digitally removing most of a scratch
>or crack in a 78 (or any other speed record for that matter). Maybe as a
>plug in for existing audio editors.
>
>Malcolm Rockwell
>
>*******
>
>On 11/27/2015 9:48 AM, Eric Jacobs wrote:
>> For those who don¹t mind a physics/mathematical representation of
>> what¹s going onŠ
>>
>> 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

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