When you put your phone on speaker mode, your phone’s microphone captures your voice without capturing the sound coming from the phone’s speakers.
If the microphone also captured the sound from the speakers, the person on the other side of the call would hear an echo of their own voice.
In this article, we’ll explain how your phone’s microphone avoids picking up the sound from the phone’s speaker in speaker mode.
How Do Phone Microphones Avoid Picking Up The Sound From The Speaker In Speaker Mode?
Your phone uses two methods to avoid capturing the sound from the speaker in speaker mode: acoustic echo cancellation using digital signal processing and dynamic adjustment of microphone gain and speaker volume.
Acoustic Echo Cancellation Using Digital Signal Processing
Your phone has dedicated DSP chips for echo cancellation. The phone knows the sound signal coming out of its speakers, so it can search for the same sound in the microphone-captured audio and try to remove that echo signal.
The phone’s microphone picks up the sound from the phone’s speaker with a slight delay. So DSP echo-cancellation chips search for a slightly delayed echo signal in the microphone audio and remove that echo signal before sending your voice to the call recipient.
Dynamically Adjusting Microphone Gain And Speaker Volume
Your phone can reduce the echo in speaker mode by lowering the microphone gain when the person on the other side of the call talks.
The phone can also lower its speaker’s volume while you talk so that the speaker won’t saturate the microphone; if the speaker is too loud, the microphone won’t pick up your voice.
However, when your phone uses these techniques to eliminate echo, both parties of the call can’t talk at the same time. For this reason, modern phones only use these methods when the echo cancellation DSP chips can’t effectively eliminate the echo.
Why Do Phones Still Sometimes Cause Echo In Speaker Mode?
Your phone’s echo cancellation is not perfect; its efficiency and accuracy depend on many factors.
The sound from your phone’s speaker bounces back from the surrounding walls, and the microphone also picks up those reflected sound waves in addition to the direct sound coming from the speaker. So the sound captured by the microphone can have many delayed versions of the same echo signal.
Additionally, different atmospheric conditions can distort the sound coming out from the speaker, altering the frequency composition of the sound.
The echo cancellation chipset inside your phone has to remove all such delayed echo signals with different frequency compositions. So your phone might occasionally fail to remove the echo in the speaker mode; echo cancellation might work perfectly in one place and fail in another.
Your phone’s echo cancellation algorithms also require some time to identify the echo signal in the microphone-captured audio, so a slight echo is normal for the first few seconds.
The echo cancellation hardware in your phone also affects how well it can eliminate the echo in the speaker mode; poor-quality echo cancellation chips might fail to remove echo even in non-challenging environments.
Conclusion
Your phone has echo cancellation chips to remove the echo signal from the microphone-captured audio; the phone knows the sound coming from its speaker, so it searches for a delayed version of the same sound in the microphone audio and removes that echo signal.
However, your phone’s echo cancellation is not perfect: the sound from the phone’s speaker bounces back from the surrounding walls, and the microphone captures these delayed echoes, making echo cancellation less accurate.
So your phone might also adjust the microphone gain and the speaker volume to reduce the echo in challenging environments.
