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Author Topic: 2-wire comms nulling question  (Read 5728 times)

Neil White

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Re: 2-wire comms nulling question
« Reply #10 on: January 30, 2016, 02:47:37 pm »

This little golden nugget is why i asked this question here.  I did not know that Star Quad made TW systems more susceptible to crosstalk, although i can understand why just by thinking about it for a second.  The client i am doing this work for SWEARS by Star Quad [for the record i do not] and i suspect ALL the wire i have been using is Star Quad.  So it looks like i need them to make/buy me some dedicated comms cables that are NOT Star Quad.

Most of our rental stock XLR is star quad because we do a lot of work in broadcast. We have a separate stock of colour coded, standard balanced XLR for our RTS comms packages.

If you are going to be buying new cable, you might want to look at the cabling requirements of the newer digital party line systems for future proofing, Clearcom has this guide HERE, and the Riedel DPL needs AES grade XLR.

For the 4w combining and splitting, any audio mixer / processor would work, perhaps something like a BSS soundweb? You could even use some spare busses and I/O from the main audio console at the event.
« Last Edit: January 30, 2016, 03:40:20 pm by Neil White »
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David Buckley

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Re: 2-wire comms nulling question
« Reply #11 on: January 30, 2016, 05:05:24 pm »

...poor nulling presents as very audible and annoying echo to my matrix panel users in DC and elsewhere.

Not a comms expert but have done a lot of video conference to audio massaging over the years.

Echo is not a nulling problem.  Nulling is about removing excessive sidetone, by adding small amount of the transmit signal polarity inverted to the receive signal.  This only works when the receive and transmit signals are time aligned.  If there is a delay involved one hears echo, and then one needs to use an echo cancellation device.
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Pete Erskine

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Re: 2-wire comms nulling question
« Reply #12 on: January 30, 2016, 06:44:05 pm »

As usual i've done a very poor job of actually describing my situation.  So i'll try again.

The ClearCom Eclipse matrix is located in a Master Control Studio in Washington DC.  Live shows are broadcast through that location from all over the world.  On the local show site [which again, can be anywhere], interface to the Eclipse system is accomplished over IP using a V-series panel locally and an IVC-32 card in the Matrix.  This panel gives me one fully functional matrix panel PLUS two individual 4W ports back to the Matrix frame.  Typically the desire is to have those two 4W ports be on two separate party lines with the two local analog PLs.  Those local analog PLs usually include a mixture of wired and wireless.  So each 4W port coming from the matrix needs to be connected to both a wireless AND a wired analog system. 

In the past i have simply converted 4W to 2W and then put both wireless and wired on the 2W.  But that has made nulling difficult.  And because of the inherent latency in an IP connection going across the world, poor nulling presents as very audible and annoying echo to my matrix panel users in DC and elsewhere.

And yes i have full programming access to the Matrix from show site using Teamviewer to screenshare back to the Eclipse configuration computer in DC.

This is what i suspected and i fully understand the principles involved. I do think that using 4W for my HME and Tempest systems is the best way to go.  So, In the above 3X3 scenario or something similar, do you have a favorite product you like to use to accomplish this?

Since you have only 2 4-wire circuits you cannot run the HME separately back to the Eclipse.  Get a second V-series panel for more 4-wire and back at the Eclipse put same channel 4-wires in the same PL channel to combine.

Another way to make this work is to eliminate the hybrid.  Make everything 4 wire.  On the hard wired TW packs do both channels need to go back to the Eclipse or can you live with just 1 back to the eclipse and the second local?  If you can do that use this method of wiring the TW channels"

The best way to make this work is to eliminate the hybrid.  Make everything 4 wire.  On the hard wired TW packs do both channels need to go back to the Eclipse or can you live with just 1 back to the eclipse and the second local?  If you can do that use this method of wiring the TW channels"

4-wire interface without using hybrid for 2-wire comms

You still will need to do some 4wire mix minus between the TW system and the HME/Tempest.  Get an audio mixer with several aux mix busses and create a mix minus for each of the 4-wire ports in your system.  A small mixer with 8X8 is the .  Beringer X32 rack mount
« Last Edit: January 30, 2016, 06:53:20 pm by Pete Erskine »
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Pete Erskine
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brian maddox

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Re: 2-wire comms nulling question
« Reply #13 on: January 30, 2016, 11:10:55 pm »

Most of our rental stock XLR is star quad because we do a lot of work in broadcast. We have a separate stock of colour coded, standard balanced XLR for our RTS comms packages.

If you are going to be buying new cable, you might want to look at the cabling requirements of the newer digital party line systems for future proofing, Clearcom has this guide HERE, and the Riedel DPL needs AES grade XLR.

Good thoughts.  It's doubtful that this company will be going reidel anytime soon, but HelixNet is a definitely possibility....
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brian maddox
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brian maddox

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Re: 2-wire comms nulling question
« Reply #14 on: January 30, 2016, 11:14:30 pm »

Not a comms expert but have done a lot of video conference to audio massaging over the years.

Echo is not a nulling problem.  Nulling is about removing excessive sidetone, by adding small amount of the transmit signal polarity inverted to the receive signal.  This only works when the receive and transmit signals are time aligned.  If there is a delay involved one hears echo, and then one needs to use an echo cancellation device.

You're right in most cases.  But in this case the transmit into and receive path out of the 2W system is about 3000 miles long via the Internet.  This introduces significant latency.  Consequently, nulling issues don't present as squeal, they present as echo.
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Pete Erskine

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Re: 2-wire comms nulling question
« Reply #15 on: January 30, 2016, 11:27:18 pm »

You're right in most cases.  But in this case the transmit into and receive path out of the 2W system is about 3000 miles long via the Internet.  This introduces significant latency.  Consequently, nulling issues don't present as squeal, they present as echo.

NO, there is an issue with local 2-wire nulling.  Without a perfect null then there is echo created.  Internet of even 10,000 miles will still only add 150-200 ms of delay which is the same as a cell phone call to the other side of the world.  Without the poor nulling, coms users would not notice the delay at all since they would not have a reference.
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brian maddox

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Re: 2-wire comms nulling question
« Reply #16 on: January 30, 2016, 11:28:12 pm »

Since you have only 2 4-wire circuits you cannot run the HME separately back to the Eclipse.  Get a second V-series panel for more 4-wire and back at the Eclipse put same channel 4-wires in the same PL channel to combine.

Yes that would be the simplest solution wouldn't it?  😀  it may just come to that.  I was just hoping to avoid the cost of an additional panel and our IVC32 card is getting pretty crowded.  Still if this is the best solution, then there it is.

The best way to make this work is to eliminate the hybrid.  Make everything 4 wire.  On the hard wired TW packs do both channels need to go back to the Eclipse or can you live with just 1 back to the eclipse and the second local?  If you can do that use this method of wiring the TW channels"

4-wire interface without using hybrid for 2-wire comms

This is quite clever.  Essentially 'crisscrossing' the two TW channels.  This might end up working quite well in this application.

I'm assuming the RTS line dryer is a standard RTS product?  I'm also assuming it would work just fine with a Clearcom TW line?

You still will need to do some 4wire mix minus between the TW system and the HME/Tempest.  Get an audio mixer with several aux mix busses and create a mix minus for each of the 4-wire ports in your system.  A small mixer with 8X8 is the .  Beringer X32 rack mount

Yeah, I'm seeing a lot of X32Racks in larger comm systems.  My client has a couple of these laying around, so that's an easy one to do if I go that route.
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brian maddox
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'...do not trifle with the affairs of dragons...

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brian maddox

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Re: 2-wire comms nulling question
« Reply #17 on: January 30, 2016, 11:31:05 pm »

NO, there is an issue with local 2-wire nulling.  Without a perfect null then there is echo created.  Internet of even 10,000 miles will still only add 150-200 ms of delay which is the same as a cell phone call to the other side of the world.  Without the poor nulling, coms users would not notice the delay at all since they would not have a reference.

Pete, you and I are saying the same thing.  Just in different ways.  I agree with you completely.
« Last Edit: January 30, 2016, 11:33:48 pm by brian maddox »
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"It feels wrong to be in the audience.  And it's too peopley!" - Steve Smith

brian maddox
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Pete Erskine

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Re: 2-wire comms nulling question
« Reply #18 on: January 31, 2016, 12:11:15 am »

This is quite clever.  Essentially 'crisscrossing' the two TW channels.  This might end up working quite well in this application.

I'm assuming the RTS line dryer is a standard RTS product?  I'm also assuming it would work just fine with a Clearcom TW line?

I built my own Audio_only_adapter

Used them on a job where a single channel had to be common in many rooms and we had only a 4 wire to each room - rather than hang a dozen hybrids on the same PL which would ring with feedback we just did this.  A common talk line on PL A and listen line on PL B - also in each room talking on channel B was local.

But Bexel - Audio specialties group sells one too  asg-aob-audio-only-box/
« Last Edit: January 31, 2016, 12:16:41 am by Pete Erskine »
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brian maddox

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Re: 2-wire comms nulling question
« Reply #19 on: January 31, 2016, 01:15:43 am »

I built my own Audio_only_adapter

Used them on a job where a single channel had to be common in many rooms and we had only a 4 wire to each room - rather than hang a dozen hybrids on the same PL which would ring with feedback we just did this.  A common talk line on PL A and listen line on PL B - also in each room talking on channel B was local.

But Bexel - Audio specialties group sells one too  asg-aob-audio-only-box/

Excellent.  Thanks, Pete.  Looks like I've got myself a build project.
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brian maddox
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Re: 2-wire comms nulling question
« Reply #19 on: January 31, 2016, 01:15:43 am »


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