# audio tempo change

snooker 20:35 01 Mar 2007
Locked

My turntable has speeds of 33 and 45 rpm which is fine as far it goes but I have a number of 78's that I would like to put on CD.
I can record a 78 at 33rpm and input it into Audacity in order to change the tempo but I can't get my head round the percentage change required.
Does anyone know the answer offhand to save me a bit of trial and error.

SANTOS7 20:40 01 Mar 2007

Many phonographs records were thin plastic discs with a diameter of 7, 10, or 12 inches (18, 25, or 30 cm). A 7 inch single is normally played at 45 revolutions per minute (rpm). A 12 inch long-playing record (LP) is normally played at 33 1/3 rpm. Old-fashioned 10 inch records were played at 78 rpm. There has been much change for the speeds of the phonograph. Due to the evolution of the way people think. An LP is able to hold about 30 minutes of sound per side.

In this essay, we are concerned with the linear speed; that is, v.

v = s /t or 2*pi*r/T

Where s is displacement, t is time, r is radius, and T is period. Since we have the diameters of the records in inches we need to convert them to the radius in meters. The period is 60 seconds divided by the number of rpm's.

For example:

A 78 rpm record with a 10 in diameter

V = 2*pi*(05 in)(.0254 m/in)(78 rpm)/(60 s/min) = 1.04 m/s

brundle 20:40 01 Mar 2007

236% speed increase

SANTOS7 20:44 01 Mar 2007

A prog called audiograbber may help ..

snooker 20:48 01 Mar 2007

Thanks a lot Brundle for quick response.

and thanks also Santos7 ....I think.

SANTOS7 20:57 01 Mar 2007

Not sure if it applies snooker, but it's a stonking bit of math, however the prog in the link WILL help,good luck...

snooker 21:10 01 Mar 2007

Thank you Santos7 - my last response crossed with yours.
The info on Audiograbber etc. is very interesting .

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