[78-L] Calculating 78 speeds in percentages

[Michael Biel]

  On 8/13/2010 12:05 AM, David Lennick wrote:
> I rely more on my ear and a good pitchpipe. Percentages aren't fixed in stone and sometimes the pitch changes subtly within a disc, and sometimes drastically. If you're playing NBC airchecks, the chimes should be G-E-C.

Not necessarily true.  It is ONLY if the chimes are the Rangertone 
Chimeless Chimes.  Practically all of the hand-struck chimes were in 
different keys depending on the model of Deagan Chimes were being used 
in that studio.  This is detailed in the web site that Michael Shoshani 
set up with help of Elizabeth McLeod and myself in providing the 
recordings.  http://www.nbcchimemuseum.info/  The earliest of the 3 note 
chimes were usually C-A-F.


> Variations of 4% aren't uncommon with some labels, especially Decca and Brunswick in the 1930s, but you'll usually have to go UP by close to that amount. Or at least 3%.

On most acousticals the speed shift would be downwards.

>> From: sjones69 at bellsouth.net
>>
>>   When using a turntable with
>> a digital read-out for the pitch shifter (like a Technics SP-15), how do you
>> calculate the percentage to get from 78.26 to other common "78" speeds like
>> 76.59, 75, 74, 80, etc.?

Those "common" speeds like 76.59 are not the EXACT speed the record was 
recorded at, it is a strobe disc speed that was the closest the 
discographer came when setting the speed by ear or pitchpipe, and was 
referenced as a speed reproducable by the reader with their own strobe 
disc.  75 and 80 are real speeds which can be counted without a strobe, 
of course.

Somewhere I have a chart that Richard Markal provided with the 
Techniques turntables he sold which list the percentages from the 
readouts and the rotational speed.  But if you MUST reproduce a 
published rotational speed,  the math is simple -- all you need is a 99 
cent calculator.  Use 78.26 as the starting point because that is what 
the SP-15 uses as 100%  76.59 divided by 78.26 is 97.866%.  Just 
subtract that from 100.00 and you get 2.134, so set the turntable at 
-2.13%.  75 divided by 78.26 is 95.83% which subtracted from 100% is 
4.17, so set the TT at -4.17%.  80 divided by 78.26 is 102.22, so set 
the turntable at +2.22%.


>> Similarly, there should be a way to determine the playback speed in RPM from
>> a record I've pitched by ear that, say, plays back at 4% below 78.26.
>> Many, many thanks...  Sammy Jones

Simple, just multiply .96 times 78.26 to get 75.12 RPM.

Mike Biel  mbiel at mbiel.com