The transmission of audio signals via the USB interface. Using IN and OUT commands and four transfer modes, audio and audio control signals are sent in USB frames from a host device (computer, tablet, etc.) to speakers and mixing equipment and from a microphone to a host device. Modes: Bulk, Isochronous, Interrupt and Control "Bulk" and "Control" transfers send audio data and control commands without errors, while "Isochronous" mode is a real-time transfer with no time to retransmit. The "Interrupt" mode is a polling method that checks the status of the host; for example, "is the Mute button pressed?"