[sdiy] RE: Forbidden Planet /HP audio osc/negative feedback

[Tim Parkhurst]

> -----Original Message-----
> From: Colin f [mailto:colin at colinfraser.com]
> Subject: Forbidden Planet (was Re: [sdiy] We are the Mummies )
> 
> >> Take a listen to the soundtrack of the film 'Forbidden Planet' made by
> >> Disney in the mid 50s.
> 
> MGM actually.
> 
> > AFAIR this was the first movie soundtrack 100% made of electronic
> > sounds.
> > And the composers / performers used modified military equipment
> > (such as radars) to generate the sounds...
> 

I have heard that one of the primary "instruments" used in the Forbidden
Planet soundtrack and for sound effects was a pair of audio signal
generators from the newly established Hewlett-Packard. I have not been able
to verify this, however. I think I found the real story on the HP website

http://www.hp.com/hpinfo/abouthp/histnfacts/
**************
"Stanford University classmates Bill Hewlett and Dave Packard founded HP in
1939. The company's first product, built in a Palo Alto garage, was an audio
oscillator-an electronic test instrument used by sound engineers. One of
HP's first customers was Walt Disney Studios, which purchased eight
oscillators to develop and test an innovative sound system for the movie
Fantasia."
**************

This was one of HP's early breaks and got them a lot of publicity. H and P
were literally working out of a garage at the time. The place is a Silicon
Valley landmark now. There is an interesting little tidbit on the HP website
if you follow the links to get information about their first audio
oscillator.

***************
"In simple terms, Bill's (Hewlett) unique contribution to the oscillator
design was to achieve excellent performance at a low cost by adding a small
light bulb to act as a "negative feedback" element in the oscillator
circuit. 

The small light bulb is set to be partially on. If the oscillator's signal
strength becomes stronger or weaker, the light bulb turns on more or less to
cancel the unwanted variations. This allows the oscillator to maintain a
nearly constant output over its designed operating range. "
**************

Okay, even back then they were using negative feedback. :)

Enough for now. 


Tim Servo

"To announce that there must be no criticism of the President, or that
we are to stand by the President, right or wrong, is not only unpatriotic
and servile, but is morally treasonable to the American public." 
-Theodore Roosevelt



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