This M21 is a mini size headphone mixer.
It helps you to mix signals from 2 ways input. Both signals are combined into a single output constantly and continually.
So you can listen to music and also hear the sounds from the other device synchronously.
You do not need to switch your cables or devices anymore.

It also can adjust line volume level via the knobs on front.
Turning 2 knobs to adjust volume on each track independently.
Our volume potentiometers turn smoothly and work durable.

Built in solid aluminum chassis: looks nice and sturdy, it is not plastic

Small size suitable for home desk audio.

It is compatible for headphone,smart phone,computer,tablet,MP3 player etc. devices that with a 3.5mm ouputs.

It is powered mixer, 3.5mm audio mixing console, stereo 2 channels headphone line mixer.

Simple Operation: Plug with the dc adapter and plug in with the cables.

Working voltage: 12 VDC (adapter included) without cables

Specification:
Inputs: 2 x 3.5mm sockets
Output: 1 x 3.5mm socket