In the related art, control devices, such as a personal computer, for editing and processing an audio signal have been proposed.  Japanese Patent No.  3896810 discloses a control device comprising: an audio signal unit including a plurality of input ports which are connected to external acoustic devices, a sound chip that has at least a microphone input terminal and a line input terminal, and a selector that connects one of the input ports to at least one of the microphone input terminal and the line input terminal based on a selection signal; a display; and a controller that is realized by an operating system including a device driver and a main CPU and that produces a selection signal and outputs the selection signal to the selector.  The controller displays, in a state where an external acoustic device is connected to one of the input ports of the audio signal unit, adjusters for adjusting at least sound volume levels of the microphone signal and the line signal; produces, when the sound volume level adjuster of the microphone signal is operated among the displayed adjusters, a selection signal to instruct selection of the microphone input terminal as the terminal to be connected; and produces, when the sound volume level adjuster of the line signal is operated, a selection signal to instruct selection of the line input terminal as the terminal to be connected. 
As standards provided for an application API for inputting and outputting an audio signal, ASIO (Audio Stream Input Output) and WDM (Windows Driver Model) are used.  In particular, ASIO is widely in use as a standard having a small latency (delay of the audio signal).  For example, an application for executing an effect process may be launched as an application corresponding to the ASIO, a desired effect process may be applied on the audio signal which is input from the microphone input terminal, and the resulting signal may be output. 
Meanwhile, there are a certain number of users, for example, who wish to launch an application corresponding to WDM to reproduce (play back) music and perform along with the music; that is, to enjoy karaoke.  In this case, because an audio signal of the ASIO application and an audio signal of the WDM application would exist in a mixed manner, these audio signals must be processed. 
In the combination of the audio interface and the computer (personal computer or the like) of the related art, the music data reproduced by the WDM application of the computer is input to the audio interface, and is output to the outside from the audio interface.  The audio signal which is input from the microphone input terminal is output to the computer and mixed with the music data in the computer, and the mixed signal is output.  When the mixed audio signal is returned from the audio interface to the computer for recording the mixed audio signal, a loop is created, and so-called howling is caused.  As a result, there had been a problem in that the mixed signal must be output to another computer or sound recording device, for recording the sound.