Better Sound for Commercial Installations

Electrical audio signals derived from the input sources are then fed to a mixer or processor that might mix a variety of input sources and/or add effects.

Mixer: This device can be used to mix multiple audio signals while adjusting their relative levels and independent sound quality. Let's look at the functions of a basic mixer, using the Yamaha MG124C as an example.

Channel Control Section: The channel control section includes individual controls for the input sources fed to the mixer, allowing adjustment of level (volume) and tone for each input signal. The following controls are commonly provided for mixer input signals:

1. Gain

Microphone signals are of a much lower level than the output from audio players (line-level signals), and must be amplified via the mixer's preamplifiers (also known as "head amplifiers") to raise them to an appropriate level. The Gain control adjusts the amount of pre-amplification applied to low-level input signals.

2. Equalizer

Many mixers feature three or four band equalizers on each input channel that can be used to tailor the sound for the best blend with the other input signals and/or to reduce feedback. More information on equalization will be provided in "Processing Types" and "Controlling Feedback (Using the Graphic Equalizer)" in Part 3.

3. Auxiliary Sends

Auxiliary sends are like "branches" off the main signal flow that will eventually reach the main power amplifier and speaker system. They can be used to divert some of the signal to external effect units, or to the performer's monitor system.

4. Pan

When the main output is being delivered via two speaker systems in a stereo configuration, the Pan control adjusts the relative levels of the corresponding channel signal sent to the left and right speaker systems. It can be used to adjust the apparent position of the corresponding input signal in the final stereo mix.

5. Channel Fader

The channel faders are used to adjust the level of each input signal. The main reason for doing this is to adjust the balance between the various input signals to create the desired "mix." The signals are electronically combined at the specified levels.

Master Control Section: The overall level of the mixed input signals is set by the STEREO OUT master fader, and the resultant signal is output via the STEREO OUT connectors which can be connected to the power amplifier inputs (the next "stage" in the system).

Processor: Processors are used to manipulate the electronic audio signal in some way, often to add effects. Processors are commonly used to increase the intelligibility of the signal and to create as natural a sound as possible. Effects are also sometimes used as creative tools. More details are provided in "Processing Types" in Part 3.

(Figure: MG124C Control Panel)