In this video, we’re going to expand more on some basic external control, and walk you through how to set up a basic fire mute using GPIO. In this example, I’ve got the 5V connection from the GPIO on the back of the processor going through a normally closed relay, then feeds back in to the GPI. The end goal here is that the fire alarm will open the relay and the voltage will drop to the GPI to trigger the mute. 
Let’s add our first GPI from the DSP into the workspace. For this example, the default Logic Binary type and settings are fine since we’re using the 5 volts from the DSP’s GPIO. These other objects are representing a basic signal flow of inputs coming in, getting processed, then going back out to our amplifiers. Ideally, we want the signal to be muted as close to the output as possible. In this case, let’s add a gain object and increase it’s channel count so that all of these channels flow through the gain object. For the gain object’s properties, we only need to make sure that Master Controls is enabled. This will give us the overall system mute that we need. 
Open the Gain object’s factory panel, and enable the selection mode switch. Simply drag the mute from the Master channel into the workspace. Now we have a logic object that’s tied to the master mute control. When this object gets a high input, the mute will trigger. Since our relay is normally closed, we should add a Logic NOT Gate in between our GPI and the logic binary for the mute. This is because when the incoming voltage is detected, it will provide a high output on the GPI object, which would normally mute the system. There are different ways to accomplish this conversion, and what’s best might be determined by the components that exist in your system. Now, we can see that so long as the voltage is coming in, the Not Gate’s output is an off state. Once we open the relay, the voltage on the meter drops and the Not Gate’s output is now on, muting the gain object. For a normally open relay, simply connect the GPI directly to the logic binary object