 Most commonly used on professional microphones, the common 3-pin XLR connector is a standard for transferring balanced audio among professional audio equipment.The 4-pin XLR connector is also commonly used on amateur radio microphones, but transferring unbalanced audio instead, and using the 4th pin (with the common ground) for a push-to-talk (PTT) circuit activated by a button on the microphone.Some broadcast radio professionals also use these microphones, instead using the PTT circuit as a cough button (a momentary mute button) so that they may cough, clear their throat, or make comments to others in the studio without the sounds being broadcast.