Echo on VoIP Calls

When Your Phones Sound Bad: Part 4 of 12

Echo on a phone call is exactly what it sounds like: you speak, and a fraction of a second later you hear your own voice coming back at you. It's distracting, disorienting, and makes it difficult to have a natural conversation. The person experiencing the echo hears their own voice delayed. The person causing the echo usually doesn't notice anything wrong on their end, which makes troubleshooting a conversation that requires cooperation from both sides.

Echo on VoIP calls comes from a few different sources, and knowing which type you're dealing with is the key to fixing it.

Acoustic echo (the most common type)

Acoustic echo happens when sound from a phone's speaker is picked up by the same phone's microphone and sent back to the caller. This is a physical audio problem, not a network problem.

Speakerphones are the most frequent source of acoustic echo. The speaker outputs audio into the room, and the microphone picks up that audio along with the local speaker's voice. Even though modern speakerphones have echo cancellation algorithms built in, these algorithms aren't perfect. They work by detecting audio that the speaker just played and subtracting it from the microphone input. But room acoustics, reflections off hard surfaces, and the volume level all affect how well this works.

If the person you're talking to reports hearing an echo, the problem is almost certainly on your end (your audio is going out your speaker and coming back through your microphone). If you hear an echo of your own voice, the problem is on the far end.

Fixing acoustic echo

Switch from speakerphone to handset or headset. A handset presses the speaker against your ear, which prevents the sound from reaching the microphone. A headset does the same thing. This is the simplest and most effective fix for acoustic echo.

Reduce the speaker volume. If speakerphone use is necessary, lowering the volume reduces the amount of audio that the microphone picks up. The echo cancellation algorithm has an easier job when the speaker output is lower.

Move away from reflective surfaces. Hard surfaces like glass walls, bare desks, and monitors reflect sound back toward the microphone. Sitting in a room with soft surfaces (carpet, curtains, acoustic panels) reduces reflections and helps the echo canceller do its job.

Check for defective equipment. A phone with a deteriorating speaker or a microphone that's become overly sensitive can produce echo that wasn't there before. If echo starts suddenly on a phone that's been working fine, the hardware may be failing.

Update phone firmware. Phone manufacturers regularly improve their echo cancellation algorithms in firmware updates. If you're running old firmware, updating may resolve or reduce echo.

Network echo (less common but trickier)

Network echo is caused by signal reflections in the network path rather than in the room. It's most commonly associated with calls that cross between VoIP and the traditional telephone network, specifically at the point where digital audio is converted to and from analog.

The traditional phone network uses a technology called a hybrid to convert between the four wire circuit used inside the telephone system and the two wire circuit that runs to your handset. This conversion is never perfect. A small amount of the audio signal gets reflected back at the hybrid, creating an echo. On traditional phone calls, this echo exists but the round trip delay is so short (a few milliseconds) that your brain doesn't perceive it as a separate sound.

VoIP changes the equation because it introduces additional delay. The audio has to be encoded, packetized, sent across the network, received, buffered, and decoded. This adds tens of milliseconds to the round trip time. When the echo from the hybrid is combined with this longer delay, the echo becomes perceptible.

Carrier grade gateways that bridge VoIP and the PSTN include echo cancellation hardware specifically designed to handle this. When echo cancellation is working properly, the gateway detects the reflected signal and removes it before it travels back to the VoIP caller. When it's not working properly, you hear your own voice coming back with a noticeable delay.

If you're experiencing echo that only happens on calls to landlines or mobile numbers (not on internal VoIP to VoIP calls), the echo is likely originating at the gateway between VoIP and the PSTN. This is typically your SIP trunk provider's equipment or the far end carrier's equipment, and the fix is on their side. Report the issue to your trunk provider with specific call examples (dates, times, numbers dialed) so they can examine the relevant gateway's echo cancellation settings.

Latency amplified echo

Even small amounts of echo that would normally be imperceptible can become noticeable when latency increases. A round trip delay of 20 milliseconds makes a tiny echo invisible. A round trip delay of 200 milliseconds makes that same tiny echo sound like a distinct repetition of your words.

This is why echo problems sometimes appear only on calls to distant locations, calls that route through multiple network hops, or calls during periods when network congestion is increasing latency. The echo was always there, but the latency made it audible.

If echo appears only under specific conditions (certain routes, certain times of day, certain endpoints), check the latency on those call paths. Higher latency doesn't cause echo, but it makes existing echo audible. Reducing latency (by improving the network path) or eliminating the echo source (by fixing the acoustic or hybrid issue) both work.

Echo on headsets

Headsets can cause echo in a few ways. Poorly fitting earpieces that don't seal well against the ear allow audio to leak out and reach the microphone. Bluetooth headsets with processing delays can create a feedback loop if their echo cancellation isn't handling the timing correctly. USB headsets with driver issues on the computer can route audio incorrectly.

If echo appears after switching to a new headset, the headset is the likely cause. Try a different headset to confirm. Wired headsets generally produce fewer echo issues than Bluetooth because they have less processing delay. Over ear headsets generally produce fewer issues than earbuds because they provide better acoustic isolation between the speaker and microphone.

Echo that comes and goes

Intermittent echo is often caused by the far end switching between handset and speakerphone during the call. When they're on the handset, no echo. When they switch to speakerphone, echo appears. If you notice echo starting and stopping during a conversation, ask the other party whether they're switching how they're using their phone.

Intermittent echo can also be caused by the echo cancellation algorithm adapting and losing its calibration. Echo cancellers continuously adjust to the acoustic environment. A sudden change, like someone opening a door, moving to a different position, or bumping the phone, can temporarily confuse the algorithm. The echo appears briefly until the canceller readapts. If this happens frequently, the echo canceller may be marginal for the acoustic conditions in the room.

Conference calls and echo

Conference calls are particularly susceptible to echo because there are more audio paths, more speakerphones, and more opportunities for audio from one participant's speaker to be picked up by another participant's microphone. A conference room with a speakerphone that doesn't have adequate echo cancellation can create echo for everyone else on the call while the people in the room hear nothing wrong.

The best conference call setup for echo prevention uses a quality conference phone with built in echo cancellation (Polycom/Poly and Yealink make well regarded conference phones), positioned away from reflective surfaces, in a room with some acoustic treatment. Alternatively, having each participant use their own headset eliminates the speakerphone problem entirely, though it changes the dynamics of an in person meeting.

Diagnosing which end has the problem

The general rule is: the echo is generated at the far end from the person hearing it. If you hear your own voice echoed back, the audio is leaking from speaker to microphone (or reflecting at a hybrid) on the other end of the call. If the other person reports hearing echo, the problem is on your end.

This means that fixing echo requires cooperation from the end that's causing it, which isn't always the end that's complaining about it. If your customers are hearing echo when they call your office, the source is your phones, even though your staff might not notice any issue on their side.

Ask the people who hear the echo to note which calls it happens on. Is it every call? Only speakerphone calls? Only calls to external numbers? Only calls to a specific office or location? The pattern reveals the source.

One more variable worth checking is latency. Echo that would be imperceptible at 20 ms of delay becomes obvious and disruptive at 200 ms, because your own voice comes back after you have finished speaking instead of blending into it. A VoIP quality test measures the round-trip latency on your connection -- if it is high, even mild acoustic leakage on the far end will be far more noticeable.

Next up: Calls Going Straight to Voicemail, why the phone doesn't ring and where the call is going instead.