Mixer is a device for processing audio, which is divided into software type and hardware type. 

Due to different principles, the application of software type mixer and hardware type mixer is also very different, the former is mainly used for audio processing, the latter is mainly used for audio settings. 

The mixer of software type is to mix multiple audio files and lines into audio signals and then synthesize a separate audio file; the mixer of hardware type is a kind of mixer that combines all kinds of audio signals (4 inputs and one output); through the internal circuit of the machine, the volume twist of each branch is adjusted and the input audio signals are mixed and output. 

To sum up, the mixing input of the software type mixer can be the digital audio file and the line input audio signal, the output is the digital audio file, and the hardware type mixer mixing input is the analog audio signal of different lines. the output is still an analog signal.