From what I have in the archive (mostly cassette) and from memories of 
my youth, the audible tones were for manual advancement and the low 
frequency (about 50-100Hz) were for automatic triggers.
Shai
בתאריך 02/08/12 4:03 PM, ציטוט Steven Smolian:
> I seem to recall that the auto-slide feature, at least for the general
> public, arrived c. 1960.  I remember the big too-doo about the Kodak
> multi-slide exhibit at Grand Cenral just before the 1963-4 World's Fair.
> When I worked there, I recall assembling shows for clients and adding the
> triggering beep which had to be at a certain frequencey.  It went onto the
> "B" channel of a 2 track stereo tape.
>
> I think many transcription houses had switched to 12" discs, especially for
> the classroom market, as that's what I remember being the size player for
> the film- record player machines of that era.
>
> If anyone really cares, a look through the audio and educational audio
> supply books of the period will have an answer.
>
> Steve Smolian
>
>
> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]] On Behalf Of Art Shifrin
> Sent: Thursday, August 02, 2012 7:52 AM
> To: [log in to unmask]
> Subject: [ARSCLIST] voca-film technology
>
> Does anyone on this list know if the disks' tones were simply cues for the
> operator to advance the slides, and or, if a frequency-tuned circuit
> triggered the next slide?
>
> Shiffy
>

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