The soundboard is the hub of studio recording and live event mixing. It is an electronic console that sound engineering technicians use to manipulate audio signals. The soundboard gathers signals as microphones and other devices receive them from a source. The mixer routes audio through channels before sending it to the speakers. Proper signal flow is critical for any type of public address system set up.
Input refers to a signal received by a device. It can also refer to the device producing the signal. Whenever a performer speaks into a microphone, or a musician plays a note, this is an example of input. Inputs capture sound, be it a digital signal or otherwise. A band member playing an electric guitar plays a chord and the input receives the digital signal instantly. Electronic devices work the same way. If you have your home computer connected to external speakers, the computer itself acts as the input, and the speakers are the output. In the case of voice and other acoustic sound, the microphone converts the audio it has captured to a electrical signal. Input also refers to the physical location on the device that receives a signal.
Speakers change electrical signal to audible sound. They are an essential part of audio engineering. Though, in live audio environments like concerts, theater performances and certain church events, speakers alone are not enough to produce the level of sound needed.
Amplifiers drive sound. They convert the lower audio signals from speakers and produce a much louder sound. Without amps, speakers would not produce loud enough sound and audiences would not hear performances.
Gain refers to the an increase of volume on the input end. Simply raising the volume of a mixing console does not adjust the gain. Gain involves manipulating the volume of the input of the sound. Again, if you have your home computer connecting to external speakers, turning up the volume on speakers merely increases the output of sound. To increase the gain, you would have to turn up the volume option on your computer, giving the external speakers more of a source to output. On a soundboard, the gain knob is located at the top of each channel strip. Sound engineers use the terms "gain" and "trim" synonymously.
When larger amounts of power flow through power cables near audio equipment and snakes (audio cables), it can result in EMI. EMI produces hums, buzzes, flickering lights, computer malfunctions and dimmer issues. Sound engineers reduce EMI by shielding (blocking the noise in metal enclosures) and/or careful placement of the audio equipment. According to WindSun.com, filtering is also an effective method of reducing EMI, however, you must have good ground in close proximity to the set up. The website states "if you have long leads between what you are filtering and ground, you could even make the problem worse."
Feedback is the loud noise that occurs when microphones pick up the audio coming from speakers. It's a cyclical effect as the microphone continuously picks up the feedback. In addition, it can damage audio equipment. You can minimize chances of feedback by proper speaker and microphone placement.