Input devices put audio signals into the system. Signals go into the mixer input jacks and are then distributed as needed. The mixer blends all the signals together to produce one stereo audio signal that can be routed along many different paths.

You can put signals to the system by either microphones or cables.

Microphones

Quality microphones are expensive but they give you the best sound and less feedback. Get the best that you can afford. This is not the place to skimp, because the best sound system in the world can’t make a poor quality signal sound good.

Placement of microphones is also important; but even that can’t compensate for a poor quality mic. The direction from which the microphone picks up sound is called the polar pattern; In other words, a microphone is designed to receive sound from one direction.

When a microphone is placed in front of a speaker, the signal feeds back into the mic’s polar pattern, resulting in feedback.

Cables

Cables carry signals to the mixer from amplifiers, or from other equipment. This type of input is called line-level input, meaning the signal is much stronger than signals from microphones. Consult owner’s manuals to ensure compatibility of devices.

Many guitar and keyboard amps have a line-level output to send signal directly into the mixer. Professionals agree that miking the amps produces better tone than playing directly into the mixer, especially when recording.

VERY IMPORTANT:

You must know how to set the mixer input level of your instruments and microphones, if you expect to have powerful sound without fighting feedback. Set the levels, one channel at a time until you complete all channels being used. 

To set a mic/instrument input level:

Set the channel’s fader to “U”, and the Master Fader to “U”. Now press the SOLO button on that channel. You don’t need amps or speakers to do this. Feed signal into the mixer channel input, just as it will be used, i.e., sing into a mic, or play, or preach, whatever you’re using that channel for. The lights or indicators show you the signal level. Use the “INPUT GAIN” knob (usually the top/ first knob on each channel) to set the level. Raise it until the level indicator reads about zero Db consistently. Do every channel that you plan to use. All EQ and AUX knobs should be set to zero and later adjusted as needed.