Comfort Noise Generation is an audio algorithm that is meant to add some static white noise to the audio signal when none exists.
The human ear isn’t used to hearing nothing at all. For long periods of time this can be uncomfort and for short ones, the user may think the session got disconnected. In a VoIP conversation, having the speakers play out no audio at all is disturbing to the listeners, especially when the speakers are a headset device worn on top of both ears.
When there is nothing to send, or the audio levels are too low to matter, comfort noise is used instead, as filler audio. Modern audio codecs implement CNG as part of the codec itself, with distinct rules and frames indicating comfort noise. Opus is one such codec.
Comfort noise is usually signaled by the sender and generated by the receiver.
