Know Your Mixer

When using the mixer you need to be familiar with the features that it has. If you read part one of this guide some of the more common features are described so that you have an idea of what to look for when getting a mixer. Knowing that the features are there is one thing, knowing how to use them is quite another. In order to get a grasp of how to achieve a goal using the controls of the mixer, in this article we will look at a basic set up for live sound. This assumes a reasonably well equipped mixer is in use but does not assume a particular model. You should always read through the manual of any piece of equipment especially a mixer. They are expensive and once they are damaged they can be very expensive to repair. Before you try anything that you are not sure of check to see what your manual has to say about it.

In order to get the best sound quality there are a number of things that you need to ensure when operating the mixer. In a previous article on PA system basics we looked at how to get a sound out of the PA system. There was a microphone connected to a channel on the mixer that caused an amplified sound to be generated by the speakers. The signal from the microphone was sent through the mixer and out again to the amplifier. Inside the mixer there are a number of stages that the signal goes through before it gets to the output stage so here is an overview.

The signal and any others will need to be set at a level that is healthy for the mixer and indeed any other equipment. A signal that is too high will result in a horrible distortion effect known as "clipping". This clipping not only sounds bad but can damage the equipment. This is so because the signal is a variation in voltage. Clipping results when a voltage that is too high is fed to one of the preamp stages in the mixer.

A basic map of the mixer.

Credit: Mike Keen

Get a Solid Mix

So lets look at how to get a good signal as far as the mixer is concerned. The mixer is the gateway to the PA system or recording machine, so if we have a good signal here, we will get a good sound out of the other end. Initially the signal is separate from any other signals that are coming in through other inputs. This is because it is fed into a channel. Channels are just like the ones on your TV (sort of)  because only one signal goes through each. This is useful to us as we want to be able to control things individually. Depending on what mixer you have there are controls at your disposal. The most important of these is the level control. The level control should be set at 0db BEFORE the gain is set otherwise you risk overloading the preamp within the mixer. Gain refers to the level of amplification that the signal in your channel undergoes. This is the control to use when you want something in the mix to be louder or quieter. The level control should be set at 0db BEFORE the gain is set otherwise you risk overloading the preamp within the mixer. With the level of the channel set the gain control will allow you to set the loudness of the signal. There may be other controls on your particular mixer's channels but level and gain are the two major ones.

Obviously there will be more than one signal that needs to be mixed, this will happen in the circuitry that comes after the channels. Methods vary between equipment and knowing the exact workings of the internal electronics is not critical. Understanding the controls and what they do to the sound however is important. Once the signal is set at a safe level it is down to you and your sense of hearing to make sure that everything that comes out of the speakers, or is being fed into a recorder, sounds good. In a recording environment headphones are useful to make a good starting point. There are several schools of thought on recording methods and it is not my intention to tell you what to do with your recording but it may be useful to record without any equalisation, so that it can be added later by various means. In a live
situation however you may need to use equalisation to cut feedback from one of your sources.

A Little Fine Tuning

Although I realise that your particular mixer may not have equaliser controls if it does it can give you the ability to really mould the sound to suit the room. Sometimes getting a particular signal as loud as the others will mean that certain frequencies that it gives out will be louder than others. An example of this is a distorted guitar. If the feedback sounds very high pitched the equaliser can reduce the high frequency from the signal so that the squeal disappears while the lower frequencies are not diminished. When you are doing this it is your understanding of frequencies and your judgement that are in play.

In order to send the sound to anywhere it is necessary to connect the mixer to the amplifier (except for powered mixers, which have their own amplifier. Most if not all mixers have a preamp before the output stage so that the mixed signals can be sent on without loss of fidelity. This preamp will have its own set of level controls and before connecting to the amplifier they should be set to their lowest setting. Also turn the levels down on the amplifier. The connection is usually via an analogue connector. Some new digital models cater for both analogue and digital output. Analogue amplifiers cannot be used with digital signals. When the connections are made you can raise the levels. Raise the level of the amplifier to 0db then raise the level of the mixer. now you can sound check and you are done. Do the same procedure when recording except instead of the amplifier you are raising the recorders level.

Well that is it for now, I hope this has been of some use but remember if there is anything you need to know that I haven't covered in my other articles then do not hesitate to ask.