Experiment: Investigating Zoom Feedback

MAY 19, 2020

Zoom, the popular video conferencing software, fails to filter speaker audio which causes feedback when using an iPad Pro that is on a desk near a wall (i.e. many desks). If the iPad Pro is upright and in the Magic Keyboard case, the feedback is especilly noticeable and disruptive.

The following is a brief writeup of an unofficial (and mostly unscientific) experiment I did to confirm and reproduce the issue.

Background

I was on what felt like the millionth Zoom call since the COVID-19 Shelter-in-Place started and decided to use my iPad Pro propped up by the Magic Keyboard case to join a meeting. Since we were having a fluid conversation in the meeting I left my Zoom client unmuted1. However, several people, as they were speaking complained about an echo and some feedback: the people speaking would hear their own voice being played back through their computer’s speakers.

After some muting, unmuting, and talking we discovered that my iPad was the only problematic device on the call. 😢 The audio I had been hearing was clear, but for everyone else in the meeting, my computer generated feedback and echo as they spoke.

In an ideal scenario, the speaker would hear nothing through their speakers (i.e. silence) and the participant’s computer would not pick up any audio that it itself played.

Experiment Setup

Since we narrowed down the issue to my device, I wanted to do a follow up in the form of an informal experiment. I wanted to experience first hand the disruptive noise my collegues were hearing.

I recorded reference audio which includes me saying The quick brown fox over the lazy dog2 which you can listen to below:

Reference Audio Visualization

Next, I configured my laptop to simulate the talker. I used Loopback to route the audio to achieve this.3 Thanks to Loopback the laptop simulated the talker using Zoom on the laptop saying the Reference Audio and recorded the audio that Zoom would be playing through the hardware speakers (had I not been intercepting it and recording it with Quicktime).

Results

As you can hear below, there is noticeable echo and feedback that’s quite obnoxious to hear as the talker.

The following audio is what the talker would hear from Zoom as they talked. It was recorded when the “bad” iPad client was upright in the Magic Keyboard case on my desk which is against a wall. In other words, it’s the audio the iPad is picking up and replaying to the other clients:

Upright iPad Audio Visualization

The following audio is what the talker would hear with the same setup except the iPad was out of the case and laying flat on the desk:

Flat iPad Audio Visualization

Notice that the disturbance is less than when the iPad is in the case.

Open Questions and Other Ideas

  1. Can we write an audio filter that better handles this type of disturbance?

  2. If I put a quilt or pillow on the wall behind my desk, would the noise disturbance stop?

  3. Is the Magic Keyboard case especially bad audio-wise? What would the disturbance be with other upright cases?

  4. Does this occur with other video conferencing software? Facetime? Google Meet? Skype?

  5. While it’s possible to hear (by playing the samples above) and see (by looking at the waveform visuals above) the audio feedback, it would be great to quantify it with some math.

  6. Is there a platform API that handles audio filtering? Video conferencing seems to be a common enough use case (FaceTime, Skype, Zoom, Meet, etc.) that it would be nice if the conferencing software could take advantage of robust filtering without needing to re-invent the wheel. (Then again, many of these companies make money by proving the “best” and “clearest” audio, so they might want to keep the secret sauce to themselves!)


  1. If you’re not having a fluid conversation and you are listening to others speak on Zoom, keeping your device on mute can help mitigate distracting noises that the other members of the call hear.

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  2. While The quick brown fox jumps over the lazy dog. is a great sample to type since it exercises the whole alphabet, it’s not a great reference for audio since it doesn’t exercise many types of sound. In retrospect, I should have use music or pink noise to capture more variety.

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  3. The setup was as follows: I configured two passthrough audio devices: Loopback Mic and Loopback Speaker. I configured Chrome audio (which was playing the Reference Audio on loop) to play to Loopback Mic which was configured as Zoom’s microphone on my laptop. I configured Zoom to route its speaker output to Loopback Speaker and then configured Quicktime Audio Recording to listen/record Loopback Speaker (which you can hear below).

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