Zoom automatic adjust volume
From IT Public Wiki
Turning off automatic adjust volume
Zoom by default has this setting enabled and while it is useful for those operating with a lot of background noise, it can be adversely effect the microphone level in our rooms that Zoom is being hosted from. To fix this, you can simply follow these settings changes:
With the application window open, select the "Settings" cog near the top right
Once opened, select the "Audio" tab, followed by the unchecking the box that is labeled "Automatic adjust volume"
Please note that if you are joining a Zoom meeting and are in a loud environment, you may want to enable this setting again if you don't already keep your microphone muted by default.