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Balanced + Unbalanced same cable same time?

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gizmo1160
Balanced + Unbalanced same cable same time?
on Jul 3, 2007 at 6:22:58 am

This is a thought i have had for some time and dont know if it is possible (think analogue)....can a balanced signal be passed down a cable and at the same time an unbalanced signal be passed back thru the same cable as a return signal?

You say NO but think of this concept.... If a balanced audio signal is the difference between pins 2&3 of the cable could another signal be put on the cable like phantom powering?
The extra signal would have to be EXACTLY EQUAL yet isolated on pins 2&3 (being equal would be canceled out in the balanced audio signal)leaving pin 1 (earth to be the other side of the unbalanced circuit).
Im only thinking line level for both send/recieve but could it be mic level from talent and line level return?

Now you ask why would you want to do this?
1. You could send t/b to a boom op in one standard 3 pin cable.
2. SNG/News links to talent would only need one standard 3 pin cable
3. Audio return from camera to portable mixer in a standard 3 pin cable
4. TV Outside Broadcasts for IFB circuits.

By this time your brain might be hurting.... but many many years ago Audio Technica did this with the AT4462 field mixer and the Modu-comm system but i have searched the net and have found very little on how they did it.

If anyone can help i would love to hear from you.




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Ty Ford
Re: Balanced + Unbalanced same cable same time?
on Jul 4, 2007 at 11:30:04 am

Phantom power is DC. Audio is AC.

Why don't you rig it up and let us know if it works?

Regards,

Ty Ford

Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. Find out more at http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com
Download Ty Ford's "Existential Boogie" from iTunes now.


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Thax
Re: Balanced + Unbalanced same cable same time?
by
on Jul 4, 2007 at 6:38:26 pm

Not so much.

As was said, the audio is AC and the phantom is DC.

The constant DC won't interact with the audible frequencies of the audio signal.

But adding another AC signal will create harmonics and cross-talk on the both signals.

There is no such thing as a "null" audio frequency signal that can be sent down a long cable... the cable inductance alone will "alter the null" as it travels the length of the wires and make its artifacts severely problematic.

FWIW, you can send an "RF" (radio frequency) signal down the same line as audio (with the proper filtering on either end) but RF is so high in frequency that it won't add any discernible harmonics to the audio signal.


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gizmo1160
Re: Balanced + Unbalanced same cable same time?
on Jul 7, 2007 at 8:09:39 am

Hi all, well i built it ( a good way to kill a wet afternoon) the short answer to does it work NO.
You can feed the signals in the original idea but does have cross talk from bal-line to unbal-line but not the other way, UNTILL you feed the input signal to the o/p as would be used on an IFB or Boom Op monitor feed.
The result= high feq. feed back.. which changed with various cable lenghts.
Overall NOT viable in the real world


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