The Bobwire RCA1 is a four channel RCA audio A/B switch. The RCA1 will automatically switch between two audio sources (4 channels each) and send the audio signal on to one output such as an amplifier(s) and/or subwoofers (2 IN & 1 OUT). The Mode switch determines whether the RCA1 will operate by audio sensing or by a 12V trigger input. An alternative setup would have a single audio source and the RCA1 will switch between two outputs (1 IN & 2 OUT) but this is only possible in 12V trigger mode. A common use for the RCA1 is to switch audio between a surround sound receiver (with preamp outputs) and a high-end stereo preamp (often called home theater bypass). Another use could be to automatically switch between a local room source and a whole house audio system. All 4 channels of the RCA1 are identical and can be used for full-range or subwoofer signals. The copper circuit board traces and the highest quality gold contact relays ensure the purest audio signal path. The ultra-sensitive audio detection circuit is 100% analog & remains out of the signal path at all times.