Re: arsclist Whirling Dervish info

[Mwcpc6@xxxxxxx]

In a message dated 09/18/2001 1:28:42 PM Eastern Daylight Time, 
m.biel@xxxxxxxxxxxxxxx writes:

> 
>  You have two vastly different machines confused.  The Whirling
>  Dervish was a pitch-shifter, which could raise or lower the pitch of
>  a sound without changing the tempo.  It could be used live, or it
>  could be used to restore the pitch of a recording which would be fed
>  to it at a different speed--thus enabling the tempo or timing to be
>  changed without changing the pitch.  It was sold by Steve Temmer's
>  Gotham Audio, and I have a brochure and a 7-inch disc with recorded
>  samples.  The reason why they were called Whirling Dervish is
>  because there is a rapidly rotating headwheel. 

I never heard of the term "Whirling Dervish" for this device but in 1965 saw 
a demo of the ELTRO "Information Rate Changer"; a large reel-to-reel 1/4" 
tape machine that could change speed with pitch correction over a +/- 2:1 
range using the rotating head drum principle. It was promoted as a language 
lab tool but I was fascinated with it because I was into recorded books and 
intelligible playback at double speed was a very attractive possibility.  
Unfortunately the $5000+ price was well beyond my means at that time.

Since then electronic means (bucket-brigade delay lines) have performed this 
function in several products available from GE, Radio Shack and others, 
unfortunately at a quality level just low enough to make them nearly useless.

I do have an application note from Gotham Audio: "An Explanation of the 
Functioning of the ELTRO Tempo and Pitch Changer" by Stephen F. Temmer that 
goes into detail on the operation of a rotating head system somewhat more 
sophisticated than the one I saw in 1965.  The application there was to cram 
more commercials into each broadcast hour, but audio quality was still a 
problem.

Mike Csontos