A thorough sound check is done for several reasons.
- Testing the system. Because of the number of components in most audio systems, initial testing must be done slowly and in the right order so no damage is done to components, mainly speakers. Before the system is turned on at all, the crossover points (i.e. specific frequencies) must be set for all the speakers so that signal power is not too great for the speakers. After this, the system components are turned on in the general order of: effects, EQ, mixer, and amplifiers. This is done with all volume and gain controls (knob that controls the small electrical signal entering the main mixer on each channel) set to zero and most other knobs at a neutral position on the mixer. Following this, the individual speakers (mid/high frequency speakers then low frequency speakers or "bass bins") are tested to ensure that only the correct frequencies are coming through them.
- Setting equalization (EQ). The main reasons for using equalization (specific frequency adjustment) in an audio system are to prevent feedback and to help create a desired sound. Of these, feedback is of the most concern and the one annoying problem that can keep cropping up throughout an event if this procedure is not done properly. The procedure is done in exactly the same way for main speakers and for monitors. The preferred method now is to use an analyzer system that compares the output of the console with what is heard coming out the main speakers via calibrated microphones in the audience. After going to all this trouble, there may still be a problem with feedback due to the different acoustics in the venue once all the event attendees are present, so EQ usually needs to be monitored continuously during the event.
- Adjusting individual channel signals. From this point on during the sound check, the band or performers should be present so they can provide information to the audio engineer as to the acceptability of their sound. For this exercise, individual channel signal inputs are tested separately. For example, the lead vocalist’s microphone is tested by first turning the gain control on that channel up until clipping or signal cutoff is shown by a light on the mixer channel. The gain is then turned down just below this level and remains there with no further adjustment during the event. From then on, the only adjustment is to the individual channel faders. The purpose of doing this is to get the maximum possible clear signal from each input source. Once this is accomplished for all channels, then the main mixer faders can be turned up and the individual channel faders adjusted to obtain a suitable overall mix coming out of the main speakers. Most audio engineers will assign a name to each channel at this time on a piece of tape and sometimes will set a preliminary level indication as well for each channel. This entire process can take quite a long time with a large band, so that time must be built into the event schedule. Here is a summary of the relationship amongst the different volume controls on the mixer:
- The gain control adjusts individual signals as they come into the mixer (i.e. individual microphones or insturment signals).
- The channel fader adjusts the signal level as it leaves the individual channel on its way to the main fader.
- The main fader adjusts the entire level of all signals as they leave the mixer on their way to the amps and main speakers.
- Setting monitor mixes. This is a procedure that in theory is very simple. The musicians onstage decide who wants to hear which of the other performers (either instruments or vocals or both) and then those specific channels are combined in the monitor mixer to create a specific mix that is sent to that person’s individual monitor. If there are only one or two mixes required as with a small band, then this mix procedure can be handled by the main mixer using the auxiliary send channels. If there are too many mixes for the main mixer, then a separate monitor mixer must be set up beside the stage and an audio technician assigned to mix the monitors full-time during the event. Of course, every musical group has different requirements so there is no set mix that can be described. What should be remembered, however, is that although the procedure is simple in theory, in practice it can be the most time-consuming part of the sound check. Event producers should keep this in mind. In the case of musical groups, Tim Lewis of Proshow Audiovisual-Broadcast in Vancouver, Canada, states how important it is to have a band that is organized for the sound check and especially for setting mixes. He cites one group that uses a method of going through the monitor mix procedure one musician at a time by having that musician play while all others raise their hands until their individual mix is perfect. This saves considerable time overall and is one of the best ways to accomplish the procedure if in-ear monitors are used.
- Setting up effects. This is usually the last part of the sound check and is done to enhance or improve overall sound quality rather than to cover up mistakes or poor musicianship. Effects include reverb (simulates acoustic effect of a large room), chorus (simulates effect of more than one person singing), flanging (makes the sound appear to "whoosh" or pulsate), and are added at this time. The procedure is really just a balancing act in obtaining a nice sound using a combination of the individual channel effects send knob and the master effects send knob (both on the main mixer), plus the effects mixture controls and the effects level knob (both on the individual effect units).