[78-L] World 1920s Records

[Michael Biel]

>> Does anyone know the cordinnates formular to play the variable speed
>> 1920s World and Vocalion record recordings at the correct speed on
>> the computer? I would like to transfere some of the dance band tracks
>> to CD. I've played around with Adobe and Soundofrge with no luck so far.
>> Jamie
From: Jeff Lichtman <jeff at swazoo.com>
> I don't know what you mean by "co-ordinates formula." Sound Forge
>> has a pitch shifting tool (under the Effects menu select "Pitch"
>> followed by the "Shift" sub-menu). You can set the number of
>> cents by which to adjust the pitch - one cent is a hundredth
>> of a semi-tone, or one twelve-hundredth of an octave.

The terminology you and many computer programs and pieces of equipment
use sometimes really confuses the situation because they are sometimes
used incorrectly and I can't tell if you are or are not.  What Jamie is
discussing are the records which run at constant linear velocity, which
means that the groove speed is constant while the rotational speed
changes as the reproducer location moves inward or outward.  The
rotation is faster at the center than at the rim.  What he means by
"co-ordinates formula" is the ratio of the starting and ending
rotational speeds so that he can restore the recording which is being
played at constant rotational velocity to its original constant linear
velocity status.

In analog the pitch and tempo remain in coordination with each other. 
Raise the tempo and you raise the pitch.  Slow down the tempo and you
lower the pitch.  THIS IS NOT PITCH SHIFTING, although many turntables
and computer programs call it by this name because they are designed by
IDIOTS, or Computer Geeks.  In digital (as well as some advanced analog
devices such as the Whirling Dervish or the Eventide) you can change the
pitch while keeping the tempo constant, or vary the tempo while keeping
the pitch constant.  THIS IS PITCH SHIFTING, and is not what Jamie
needs.  

Jeff, what do you and Sound Forge mean?  From the daze of numbers below
it sounds like you are shifting the pitch, and then making an adjustment
to the mechanical rotational speed of the record.  That louses things
up.  What Jamie needs is some way to play the record at constant
rotational speed and vary the pitch and tempo TOGETHER in the computer. 
 

Mike Biel  mbiel at mbiel.com 

> There's a simple formula to convert a frequency ratio to cents. 
> Suppose you have a signal of 430 Hz, and you want to speed up the 
> recording to where the signal is 440 Hz (concert A). The formula is:
> cents = 1200 * (log(desired frequency / current frequency) / log(2))
> In this case, it would be:
> cents = 1200 * (log(440 / 430) / log(2))
> The base of the logarithm doesn't matter as long as it's the same
> in both the numerator and denominator. Using the natural log, we get:
> cents = 1200 * (0.022989518224698739423565307535635 / 
> 0.69314718055994530941723212145818) cents
> = 1200 * 0.033166863935199317315221406257726 cents
> = 39.800236722239180778265687509271
> Rounding to one place after the decimal point, we see that we
> need to speed up the recording by 39.8 cents. - Jeff Lichtman