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Kearnstd
Space Elf
Premium
join:2002-01-22
Mullica Hill, NJ
kudos:1

what makes a phone Echo?

working in tech support i take tons of calls, what makes some people's phones have nasty echos where you hear yourself talk? is it bad phone circuits that the speaker and mic circuits cross or is it something in the phone system with the switches? or more of the "please turn down your radio effect"?
--
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Boricua
Premium
join:2002-01-26
Sacramuerto

I have experienced that before and what I've done is tell the person I'll call them back in a few minutes. Doing that usually cures the problem.
--
Yo te digo, el mundo esta jodido


chandom

join:2001-05-23
Tallahassee, FL
reply to Kearnstd

In some cases the caller might have you on speaker phone.



tschmidt
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reply to Kearnstd

Land lines originate as an analog 2-wire circuit. At the Central Office or Remote Terminal voice is digitized. This requires the magic of a hybrid-transformer. . Hybrid transformers are very old technology used to convert 2-wire circuit(Tx/RX on same wires) to a 4-wire circuit (TX & RX each on dedicated circuit).

Nothing is prefect so if lines are not well balanced some transmit energy leaks into the receive circuit. The greater the leak the louder the echo. As end to end delay time increase echo becomes more and more annoying.

There is also a hybrid transformer built into each phone. It is used to couple microphone and earphone to 2-wire line. It is intentionally designed to leak a little transmit energy into the headset called sidetone. This allows talker to hear what they are saying in the earpiece.

Various impairments cause some transmit energy to be coupled into the receiver. As end-to-end delay increases a given amount of echo become more objectionable.

/tom



coxta
Ultramundane
Premium
join:2000-07-15
LALALALALALA
reply to Kearnstd

tschmidt, you see to have the handle on it. I had heard that it was related to satellite signal propagation. In this case, even though it is line of site, there might be multiple paths to and from the satellite. I wonder if you have some comment about the truth of that statement.

thanks.
--
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TherapyChick

join:2003-09-19
Fayetteville, NC

2 edits
reply to Kearnstd

said by Kearnstd:

what makes a phone Echo?
Are they in a canyon?
Are they in a canyon?
Are they in a canyon?


tschmidt
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reply to coxta

said by coxta:

I had heard that it was related to satellite signal propagation.
When you say Satellite I assume you mean geosynchronous satellites.

The problem with geosynchronous satellites is the extreme distance.
»en.wikipedia.org/wiki/Geosynchronous_orbit

They are about 25,000 miles high so trip each way is 50,000 miles if satellite is used in both directions that doubles to 100,000 miles. That means it takes about a half second for round trip.

High latency are not a big issue for recorded transmission but adding that much makes voice calls virtually unusable. Any echo that is present is now much more noticeable since it is delayed so much.

/tom


swintec
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reply to Kearnstd

In the VoIP world, this is related to the transmit and receive volumes being to high. I had this when I originally got my VoIP service, I turned down the volume in my ATA for both directions and it cured it.
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Combat Chuck
Too Many Cannibals
Premium
join:2001-11-29
Verona, PA
reply to Kearnstd

said by Kearnstd:

working in tech support i take tons of calls, what makes some people's phones have nasty echos where you hear yourself talk? is it bad phone circuits that the speaker and mic circuits cross or is it something in the phone system with the switches? or more of the "please turn down your radio effect"?
If you're working in a call center that also happens a lot when they are monitoring a call.
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dmagerl
Premium
join:2007-08-06
Woodstock, IL

You obviously dont remember the days before digital T1 long distance lines. The quality of those calls were horrible.

Echo can also be caused by broken/improperly set up echo cancellers. Every CO has them, they do die.

As someone else explained echos are a fact of life due to the 2-wire hybrid used in the telephoone instrument itself.

-dickm



dvd536
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Phoenix, AZ
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reply to swintec

said by swintec:

In the VoIP world, this is related to the transmit and receive volumes being to high. I had this when I originally got my VoIP service, I turned down the volume in my ATA for both directions and it cured it.
You have a magicjack too huh?
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Mele20
Premium
join:2001-06-05
Hilo, HI
kudos:5
reply to dmagerl

Years ago, I considered myself very lucky if there was no echo on phone calls from the Big Island of Hawaii to the Central or Eastern USA mainland. These days, I seldom get an echo. I did about a week ago though when calling a business in Florida. The CSR could not hear the echo but it was driving me nuts so I hung up and called back and it was ok. While I seldom get an echo to the Mainland these days, I get horrible echos (and line static) to India and the Philippines so I really hate that so much computer related tech support has gone to those two locations. Coupled with accents it makes it almost impossible to understand anyone in those locations.
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swintec
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reply to dvd536

said by dvd536:

said by swintec:

In the VoIP world, this is related to the transmit and receive volumes being to high. I had this when I originally got my VoIP service, I turned down the volume in my ATA for both directions and it cured it.
You have a magicjack too huh?
Nope, not at all...this can happen with any VoIP provider.
--
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Jameson
Premium
join:2004-05-28
Fallbrook, CA
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reply to TherapyChick

said by TherapyChick:

said by Kearnstd:

what makes a phone Echo?
Are they in a canyon?
Are they in a canyon?
Are they in a canyon?
well
well
well


Subaru
1-3-2-4
Premium
join:2001-05-31
Greenwich, CT
kudos:1
reply to tschmidt

said by tschmidt:

said by coxta:

I had heard that it was related to satellite signal propagation.
When you say Satellite I assume you mean geosynchronous satellites.

The problem with geosynchronous satellites is the extreme distance.
»en.wikipedia.org/wiki/Geosynchronous_orbit

They are about 25,000 miles high so trip each way is 50,000 miles if satellite is used in both directions that doubles to 100,000 miles. That means it takes about a half second for round trip.

High latency are not a big issue for recorded transmission but adding that much makes voice calls virtually unusable. Any echo that is present is now much more noticeable since it is delayed so much.

/tom
I don't think they use a satellite as much as they used to for very LD calls as much as they used to now..

I always been interested in this.. I went to the Air and Space in Wash. D.C and I remember seeing some equipment that was on display which was used to cure the echo issue back in the day in the early 90's.
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tschmidt
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said by Subaru:

I remember seeing some equipment that was on display which was used to cure the echo issue back in the day in the early 90's.
Echo cancellation is still very much in use today, now it is done with DSPs rather then dedicated hardware.

»en.wikipedia.org/wiki/Echo_cancellation

Even though telephone circuit is full duplex (both sides can talk at the same time). In actual use only one person is talking at a time, other is silent. Echo cancellation takes advantage of that and attenuates line on the non-talking direction. The added attenuation reduces level of remote far echo improving call quality. When both sides are talking attenuation is removed. In that case speech helps mask echo.

/tom


Subaru
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Greenwich, CT
kudos:1

Hmm I did not know that.. I only on some phones if no one is talking it's like the microphone gain slowly goes up until someone speaks.

I've had phones like my HTC Wizard with it's dual speakers that is so loud it echo's back into the mic under the phone..

I've called places like Japan, Turkey and Thailand and had no echo at all.



shdesigns
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reply to tschmidt

said by tschmidt:

Echo cancellation is still very much in use today, now it is done with DSPs rather then dedicated hardware.

»en.wikipedia.org/wiki/Echo_cancellation

Even though telephone circuit is full duplex (both sides can talk at the same time). In actual use only one person is talking at a time, other is silent. Echo cancellation takes advantage of that and attenuates line on the non-talking direction. The added attenuation reduces level of remote far echo improving call quality. When both sides are talking attenuation is removed. In that case speech helps mask echo.

/tom
Actually echo cancellation works by creating a predicted echo and subtracting it from the received signal.

It works the same if one or both sides are talking. The only difference is the echo prediction is only updated when one side is talking.

I have written echo cancellers. Most implementations I have seen only handle about 30ms of delay to handle local echos. A longer echo takes more processing and memory and has issues of divergence.
--
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Epikos
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join:2003-07-27
Hillsboro, OR
reply to Kearnstd

In the call center I work in, our Avaya phones sometimes echo when we're on headsets.

If you lift the handset and put it back down, it fixes the echo.
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