[AV Media Matters] Speed correction (was playingat1 7/8 and 3 3/4 ips)

[TrevWeb@aol.com]

Stuart Rohre writes:

<< Another speed correction technique for audio recordings from poorly
speed
 regulation portables is the play the originals on an instrumentation
type
 playback deck that has external servo speed control.  You can connect
an
 audio oscillator of the appropriate servo control frequency, and tweak
the
 exact speed control frequency to improve the voice quality. 
 Record copies on a high quality speed controlled deck. >>

Many years ago, when I was still in short trousers, the BBC used the
battery 
powered EMI L2 recorder for location radio reports.  The reporters were
not 
very fastidious about checking battery condition and the recorders would

often run more and more s-l-o--w---l----y.  When played back in the
studio, 
of course, the voice got higher and higher.  

The solution, rather as Stuart suggests, was to modify a studio replay 
machine such that the deck mains supply was powered from a separate
socket.  
This was fed from an enormous ex-army audio amplifier - allegedly,
designed 
for instructing trainee parachutists - on the way down!  The amplifier
was 
fed with a signal generator, capable of giving 50 Hz of less and the 
frequency was judiciously tweaked as the variation in the voice seemed
to 
require.  The synchronous motor followed the false mains frequency down
to 
very low speeds.

It all sounds very crude now, but it worked extremely well.  How much
easier, 
though, in these days of crystal control.

Trevor Webster

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