When audio is present in a recording, the rate at which the recording can play ranges from 0.5 times (half-speed) to 8 times. Audio remains audible at these rates. For even slower rates, and faster rates, the audio must be discarded. Playback rates with the audio discarded, or if no audio is present, is from 0.1 times (1/10th speed) up to 120 times. This is not 120 FPS, this is 120x: 120 seconds of playback passes by every second.
The original recording is not affected; the audio remains in the recording.
Like LAN/WAN select, Discard audio is a client-side System panel state setting, stored in scp_L.txt.