> Mixer Overview Part 1: The Channel Strip

On a lot of modern mixers, the channel strips are offered in two forms, Mono Channels and Stereo Channels. The mono channels are designed primarily for instruments and microphones, while the stereo channels are designed more for stereo synthesizers and effects processors. Because of this, some aspects are slightly different. Let's start by looking at the channel's inputs and outputs.

The mono channels feature a Direct Output This is a line level signal that is great for sending to a recording device or computer soundcard. This output can be set to Pre-Fader or Post-Fader (we'll get into more about this later in the article, but basically pre-fader means moving the fader does not effect the output volume, and post-fader means that it does). The Microphone Input is a LO-Z (low impedance) input that you can plug a microphone directly into. It provides both a pre-amp and a 48v phantom power supply for use with passive condenser microphones. The Line Input allows you to plug in any line-level device, and can also be used with an instrument level device such as an electric guitar. The Insert is a different type of connection. It is both an input and an output at the same time. By using an insert cable, you can add external effects to the signal. For example, if you have a vocal microphone plugged directly into the board, you can use the insert to route the individual signal through a compressor before it is mixed with the other signals.

The stereo channels on mixers are usually much simpler, since stereo devices typically have more sound shaping options built in. In the case of inputs, you are provided with a Left Input and a Right Input which as you can guess, is where you plug in the left and right signals from your stereo device.

From here, we reach the channel's Gain control. This controls the volume of the input signal before it is sent through the rest of the mixer. Why do you need a gain control when you have a volume fader already? Well, if the original signal going into the mixer is too strong, then it will overdrive the mixer and sound too distorted. But, if the signal is too week going into the mixer then it will be noisy when the final volume is brought up to a usable level. This goes into the process of "Gain Staging". What this means is that any point in the path of an audio signal that allows you to chang the volume can alter the signal quality. In the mixer, this is the first gain stage. Setting the signal volume before it goes into the mixer is also part of gain staging.

Next is the Equalizer or EQ section. This is where you can adjust different frequencies of a signal. Like the inputs, this section is different on mono channels then on stereo channels since most stereo devices have some sort of equalization built in. On the mono channels of the M12, the EQ starts with a Low Frequency Roll-Off at 100 Hz. This simply eliminates any frequencies below 100 Hz, which is great for keeping guitars or keyboards from getting in the way of a kick drum or bass. Next is the HF knob which raises or lowers the frequencies of high frequencies. Similar is the LF knob which controls low frequencies.

The mono channels also feature two MID knobs which control mid range frequencies. The first knob lets you select the range that will be effected, while the second controls how much to raise or lower the volume of the selected frequency. This allows you to lower unwanted noises, accent the snap of a bass guitar, or help a vocal or lead track cut through a mix better.

So far, we've talked about how to get the signal into the mixer and how to alter the signal. Now we'll get into how to route the signal to other devices by using Aux Sends. Aux sends, or auxiliary sends, let you send the signal to external effects processors, into a recording device or soundcard, or even make separate sub-mixes for monitoring purposes. Since aux sends are shared by all of the mixer channels, you can think of them as smaller mixers within the mixer.

When talking about the direct out earlier in the article, we went over pre-fader vs. post-fader. On the Soundcraft M12, aux 1 and 2 are always pre-fader, and aux 3 and 4 are always post-fader. This is different on some other mixers. Post-fader sends are great for effect sends such as reverb. This will allow you to set the reverb level per track by raising the aux knob, and when you change the volume of the track, the aux send amount will change too, giving you a consistent wet to dry ratio. Post-fader sends are great for sending a signal into a recording device or soundcard since you can set the send level independently of the volume you are listening at.

If you are using the aux sends to route the signal to an effects processor, then you can also take advantage of the Aux Returns which let you monitor the output of the effects without having to use up more mixer channels. We'll get into that more later, but for now we'll follow the signal a little further through the channel strip.

Ok, now it's time to finally learn how to "mix" the signal with the signals on the other channels. But, before we combine all of these signals together, we have to tell them how to interact with each other. The first step in this, is the Pan knob. A "pan pot" or "panoramic potentiometer" tells the signal where to sit in the "stereo spectrum". In more basic terms, setting the pan knob to the middle position means that you'll hear an equal amount of the signal in both the left and right speaker, creating the illusion that the signal is coming from a space somewhere in the middle. Moving the knob to the left decreases the amount of signal sent to the right speaker, making the signal appear to be moving to the left, and turning it to the right does the opposite.

The stereo channels will have a Balance knob instead which is very similar, but works slightly different. With a stereo channel, there are two separate signals, one for the left speaker, and one for the right. Turning the balance knob to the right will decrease the volume of the left signal, while the right signal will remain unchanged. It is important to remember that turning the knob all the way to one side will not put both signals on the same side, but instead cut out one of the signals all together!

The next stop on our tour of the mixer is the Mute button. Pressing this button simply turns off the signal from the channel. (Some mixers will have an "On" button instead which simply works in the opposite manner.) Why do you need a mute button when you can just turn down the volume? Well, there are two reasons. First, the mute button is slightly faster, but most importantly, you don't need to worry about forgetting what volume the channel was at, since the volume controls never move. Easy enough? Ok, let's move on.

On the mono channels of the Soundcraft M12, the next button is marked Direct Pre. Remember the direct output we mentioned earlier in the article? This is where you set the output for pre-fader or post-fader. On other mixers, this control may be located in a different location.

Now we get to the PFL or Pre-Fader Listen button (called "Solo" on some mixers). Pressing this button takes the channel's signal before the fader, and sends it directly to the mixer's output while muting everything else. This is a great way to concentrate on a single aspect of a mix without changing any levels. When using this button, remember that you will not be able to control the volume with the fader, so it's usually a good idea to turn down the speakers a bit first.

Our signal has gone through a lot since entering the mixer. How do we keep up with it? Each mixer channel provides two LED lights marked Sig and Peak. The green sig light lets you know that there is a strong signal present on the channel. This way you can easily see what channels are playing and which are not. The red peak light warns you when the signal is too strong, and is being clipped or distorted. If your signal is too weak or too strong, the gain knob (remember that thing?) can be used to adjust it.

Finally we get to the Fader. This is the most recognizable, and most useful feature of a mixer. This lets you adjust the signals volume before it is finally mixed with the signals of the other channels. This is the last piece that the individual signal will pass through before being combined with the other signals. Unlike a typical volume control, setting the fader to 0 will result in no change in the signal strength. Moving the fader up or down from 0 will increase or decrease the signal's volume by the amount of decibels shown. Setting the fader all the way down will stop the output completely.