Is there a product that will apply power to my car amplifier only when music is actually playing? The amp(s) have a sense circuit that let them operate on/off when the radio is on/off, however, I'm using a car computer that has no such output circuit. I'd like to put the sound card signal into a box inline with the amplifier and have that box control the amplifiers turning on when the volume level reaches a certain level and then stay on for a predefined delay period.

The reason for this is that the computer has no output like a car radio to turn on an amplifier so I wire the amp radio sense to accessory and amps come on with ignition switch. The computer always puts out some low level noise, be it white noise or processor RF, especially before the sound card is initialized while booting. The amps being on all the time with the ignition switch makes it annoying.

Audio Players & Recorders - NAD - C320 2-Channel Amplifier