The Preamp Section (Mixer Fundamentals)

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The input section of a mixing console is made up of channel strips, each one for a separate input source. And even though these look completely different on analog and digital, the signal chain is pretty much the same on all consoles. First comes the preamp section, then the EQ section, followed by the pan mute, and then the fader section. There's a lot here, so we'll cover this in two videos — first the preamp section, and then the rest of the channel strip.

In this video, we look at the preamp section, which includes Pad, Phantom Power, and Polarity options. It also has the High Pass Filter setting, which helps us keep a mix clean, as well as the insert, which lets us use dynamics processors, like gates and compressors.

The mixing console takes inputs from microphones, DIs, and other line level sources, each of which gets its own channel strip. So, we can think of each channel as the control for one input. And as I mentioned, the signal chain is the same for both analog and digital, even though you can adjust the order on some digital mixers.

When we connect an input source to the console, the very first thing the signal hits is the microphone preamp, or mic pre. This is controlled by the gain knob, and properly setting the gain is the very first step to getting a solid mix.

Really, the gain knob is the most important knob on the console. Since this is the first thing in the signal chain of the console, it affects everything else that comes after it. So, we do take a look at some tips for setting the gain in the next video.

The preamp also has a pad button, which cuts the signal by a fixed amount. This comes in handy when the input signal is so hot that it's clipping the mic pre, even when the gain is all the way down. The pad button then brings this down by something, like, 20 or 30 dB, which is hopefully a more useable signal.

Most consoles also have a polarity switch in the preamp section, which is important for professional audio engineers, but a little beyond the scope of this course. We also have a phantom power button, which sends 48 volts of current through the mic cable to power condenser mics or active DIs.

Even though it's technically an EQ, the high pass filter, or HPF, is also found in the preamp section. This lets the high frequencies pass, while cutting the low frequencies.

High Pass Filters are used pretty heavily by most live sound engineers, and they are really helpful for getting clean sounds on cymbals, guitars — and definitely also voice — by keeping unnecessary low frequencies out of the mix. Some small analog consoles just do a fixed cut at around 100 Hz, but on professional consoles, you can adjust this, and I even high pass vocal mics up to 160, or even 180 Hz, depending on the situation and what sounds best for that singer's voice.

At the end of the preamp section is the insert, which is where we have our gates and compressors. Analog consoles don't have these built in, so you have to physically connect outboard gear. But on digital consoles, gates and compressors are built in to every channel, and we talk about this more later. I also show you some audio examples so you can hear what these sound like.

Something important to note here: the insert is in-between the preamp section and the rest of the channel strip. So, while it comes after the preamp, which includes the HPF, it comes before the EQ, Fader, and Aux Sends, both pre and post. This can be changed on some digital consoles, but in audio, it's always a good idea to have a clear picture of the signal chain.

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