Sidetone sends any input to whatever output you pick. Usually that means hearing your own microphone while you talk, but a line-in works just as well. It's free and open source.
Capture and playback run on independent clocks, joined by a ring buffer that corrects for drift, so a USB mic into Bluetooth headphones keeps working instead of slowly falling apart.
What it does
- Mic monitoring on Mac: pick an input and an output, flip the switch, and hear yourself.
- Gain in dB that ramps as you drag, a level meter, and a spectrum so you can see sound arriving.
- A low cut, bass and treble, and presets for the devices and settings you use most.
- ⌥⌘M starts and stops monitoring from any app, with an optional hold-to-mute key.
- Follows the system default devices, so putting headphones on moves monitoring to them.
- Warns about feedback before you send a microphone to speakers.
Not just microphones
Anything the Mac sees as an input works. A common use: a games console on a monitor's picture-in-picture input has no sound, because monitors only play audio from the main input. Feed the console's audio into a USB line-in, point Sidetone at it and send it to the monitor's speakers, and you can hear the console while the Mac keeps the main picture.
Install
Sidetone needs macOS 15 or later. Open the DMG and drag Sidetone into Applications. It's signed and notarized by Apple, so it opens like any other app.