a question about balanced cables...

Posted on

eeeeeeemo.
Member Since: Oct 30, 2003

ok, i thought i understood the construction and uses of balanced cables until my music tech lesson today, which has just confused me

originally i thought that your audio signal was sent down one wire in the cable, while no signal was sent down the second wire, leaving just noise on it; and as these two signals were 180 out of phase, the noise on the second wire cancelled out noise on the first wire, leaving a relatively noise free signal

yet today i was told that the same audio signal is sent down both wires, 180 degrees out of phase. surely these signals would cancel each other leaving silence??

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Prince CZAR-ming
Member
Since: Apr 08, 2004


Dec 01, 2004 11:26 am

I think, that both signals (180 out of phase) will collect noise that is in phase with itself (the noise). When the signal is flipped at the end, the two noise signals become out of phase with each other, thereby cancelling itself out.

Hopefully I got that right, it's been awhile since I read on that.

Someone please correct me if I'm wrong.

Prince CZAR-ming
Member
Since: Apr 08, 2004


Dec 01, 2004 11:27 am

Oop, that should be when ONE signal is flipped at the end, not when the signal.

Bane of All Existence
Member
Since: Mar 27, 2003


Dec 01, 2004 11:45 am

yeah one signal gets flipped at the beginning, putting them 180 out of phase. then that signal gets flipped back, putting whatever noise hopped on during transit out of phase with itself, but the normal signal is back in phase with itself.

eeeeeeemo.
Member
Since: Oct 30, 2003


Dec 01, 2004 12:03 pm

ah ok. think i understand now. i'll have a google and see if i can find any further reading on it... anyone knows any links?

eeeeeeemo.
Member
Since: Oct 30, 2003


Dec 01, 2004 05:36 pm

ahaaa, for anyone else who needs help understanding this topic, see here: www.mediacollege.com/audi...e-balanced.html

Chief Cook and Bottle Washer
Member
Since: May 10, 2002


Dec 01, 2004 10:55 pm

That is cool!

Checked my mixer and for sure that is what is going on. There are two op amps with inverted phase feeding the main out XLR's. Makes sense now that I see it done. No chance for a ground loop that causes most noise. And obviously any noise collected would be traveling in phase and therefor be canceled at the point of re-inversion.

Thanks for sharing!

eeeeeeemo.
Member
Since: Oct 30, 2003


Dec 02, 2004 12:27 pm

one more question.... do all balanced cables have two antiphase signals sent down them, or will this only happen if you use balanced inputs/outputs (if such things even exist....?)

Prince CZAR-ming
Member
Since: Apr 08, 2004


Dec 02, 2004 12:37 pm

No, only if you have two devices with balanced in and outs.

For instance, an xlr cable will carry balanced signal between two balanced jacks, the same xlr cable will only carry unbalanced signal between two unbalanced jacks. I beleive a TRS 1/4" plug (stereo plug) can carry balanced signal as well if the jacks built into the device(s) are wired for balanced signal. Actually I think the M-Audio breakout boxes are balanced 1/4" jacks.

So to answer your question, if the device has a balanced jack, and the cable is 3 conductor, then it will send balanced signal. If the cable is 3 conductor, but the device is wired non-balanced (think 2 conductor), then the signal will not be balanced.

Hope that made sense.

eeeeeeemo.
Member
Since: Oct 30, 2003


Dec 02, 2004 02:06 pm

aye it did, thankyou muchly

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