Definition
The sound of a pilot's own voice fed back into their headset or headphones as they speak into the microphone. Sidetone is produced by the radio or intercom system so the speaker can hear themselves transmitting at a natural-sounding level.
Plain English
When you talk on the radio, you hear your own voice in your headset. That feedback is sidetone. It tells you the microphone is picking you up and lets you judge how loud you are speaking.
Context Anchor
You encounter sidetone when using a headset, aircraft radio, intercom, or audio panel, especially while checking whether your microphone audio sounds normal.
Derivation
From 'side' (alongside, as a secondary path) plus 'tone' (sound). The term originated in early telephone engineering, where a small portion of the speaker's voice was routed back to the earpiece so the call did not feel dead. Aviation radios borrowed the same idea.
Why Pilots Care
Confirms the radio is transmitting and helps pilots adjust speaking volume and clarity for ATC.
Analogy
It is like hearing a small amount of your own voice in a telephone earpiece while you speak, so you know how you sound.
Intuition Check
Sidetone is not a tone from another aircraft or from air traffic control. It is your own voice being fed back to you while you transmit or speak on the intercom.
Example Sentence 1
During the radio check, the pilot noticed there was no sidetone in his headset, so he suspected a problem with the microphone circuit.
Example Sentence 2
I turned down the sidetone level to reduce distraction while copying a complex clearance.