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Nor me. I used a 10% frequency-adjustable 12kHz notch filter that originally came with the Altec mag tube preamps. It never made that 12kH inaudible. I also found out that in the heads I had, and I am sure you will find this in most of the older original penthouse heads, the 12k bleeds into the other heads right in the head cluster itself, especially the track that is right next to channel 4....what is that, the Center channel or Left, I can't remember).

You need to listen to the film played with the surround off and with only the front channels playing. If you still hear the tone, then you have a bleed problem, and I'll bet it's not your electronics down the line, but it originates right in the head cluster itself. I mean they recorded that damn thing at 0db -- were they on crack when they thought up this system? I am sure at 0db it regenerates itself into the coils of the other heads in the cluster by sheer induction. The old literature kept referring to the 12kHz tone as "inaudible." Yeah, maybe to someone in their 90s.

What I wound up doing was buying three additional, high-quality Altec studio notch filters for the other three front channels. Also, the speed of the machine may affect the amount of attenuation the notch filter can achieve; if the machine is running faster or slower than precisely 24fps, that tone will be slightly off and the filter will not be hitting it right on the head. But you have to be really off to make a significant difference.

We never used the original relay to kill the surrounds in our jerry-rigged setup -- we used a piece of studio gear called an Auto-Attenuator; it was a neat little compact unit made by Fairchild that simply attenuated a signal whenever it dropped below the level you set. It was a piece of cake to align -- you just passed the surround signal through it and played a reel with a section with no surround audio (except whatever bleed was present from the front channels -- the reason for the 12kHz trigger in the first place). Then you set the unit threshold control so that the unit completely attenuated the signal. When the surround audio kicked in, you set the threshold on the unit to pass the signal. It worked like a charm. Only recently did I replace it with a Valley People compander with fifty-million controls on it that all have to be precisely tweaked. I moved to the compander only because it can be used to add a bit of downward expansion for the surround channel on Dolby A & SR prints, helping to slightly attenuate the crosstalk in quite passages -- good for the folks who are not in that perfectly timed-delayed sweet spot -- a real help in large halls like ours.

Thankfully it didn't take them long to see the error of their ways and they began releasing mag prints with no trigger tone at all --dropped it like the rotten hot potato it was. I have played many mag prints with no 12khz trigger, just audio on track 4. Nice thing about the Auto-attenuator, it doesn't care if there is a tone or not, it still worked fine, cleaning up crosstalk even though there was no trigger tone because it uses the audio level itself to activate the attenuation factor. Come to think of it, you could also adjust the decay time which allowed the unit to gently reduce the volume when the tone disappeared, unlike the original relays which just clicked the speakers off abruptly.

BTW...it is the 364 not 360. The 364 was cinema specific and had "clean-up" mode.

Steve

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Thankfully it didn't take them long to see the error of their ways and they began releasing mag prints with no trigger tone at all --dropped it like the rotten hot potato it was. I have played many mag prints with no 12khz trigger, just audio on track 4. Nice thing about the Auto-attenuator, it doesn't care if there is a tone or not, it still worked fine, cleaning up crosstalk even though there was no trigger tone because it uses the audio level itself to activate the attenuation factor. Come to think of it, you could also adjust the decay time which allowed the unit to gently reduce the volume when the tone disappeared, unlike the original relays which just clicked the speakers off abruptly.

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Do you know when they dropped the 12 kHz. tone? I agree, it was a bad system, I know there were a few 4 track releases with Dolby A, it would seem highly probable that these did not have it, but was it dropped before then? I want to install it in the setup that I am doing, mainly for historical completeness, but I don't know if it will ever be used, other than for demonstion purposes.

Most of the 4 track shows I saw seemed to make no use of the surround channel anyway, did many films not use it, or did the cinema just turn it off, possibly due to problems with the 12 kHz. system.

I can think of three cinema sound systems which used control tones for vaious purposes:

The Fantasound TOGAD.

The Cinemascope 12kHz suround switch.

Perspecta.

Were there any others?

It is interesting that the oldest of these systems (Fantasound) was the only one which kept the tones on a separate track, both of the others combined them with the programme sound, thereby causing problems with eliminating them in the theatre, and limiting the bandwith available for the audio. Seems like a step backwards to me.

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Mag -- it had it's problems, but it was a sweet-sounding, DISCRETE system -- a claim Dolby, as much as they bad-mouthed the mag system in their early manuals, could never make.

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It is definatley CP-100 era...the Cat. 91 is in the CP-100, the Cat 92 is in the MPU and the Cat. 80 series stuff is in the CP-100 as well.

Steve

Steve

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