This article gives a simple overview of the processes of connecting instruments and microphones to the input stage (pre-amp) of a mixer input channel. Although most people without a technical understanding will be able to connect guitars, keyboards and microphones to a mixer channel successfully, it can be helpful to understand the underlying principals to ensure you are maximising dynamic range and therefore signal quality.
When plugging a sound source into a mixer input channel we must follow a safe procedure. This is for a number of reasons ...
In the studio the difference between the quietest and the loudest source signals can be huge. There are 3 categories of signal which instruments and sources create ...
The control for the input stage of
a mixer (pre-amp)
To accommodate the huge difference in level and impendence between Mic and Line signals, each input channel of a mixer has two input circuits, Mic Input and Line Input. The Mic input circuitry will be fed from an XLR (Canon) socket. The Line input circuitry will usually be fed from a Jack socket, either unbalanced (mono jack) or balanced (stereo jack or XLR).
A Mic/Line button will allows the appropriate circuit to be selected for the source signal. Note that by the time the mic and line signals get to this button they will both be at line level, the mic level signal having been converted by a mic pre-amp circuit.
A pad button will allow the input signal to be reduced by typically 10-30dB if it is overloading the circuitry.
To send phantom power to an active DI box or condenser mic.
A gain control will allow you to turn down the signal so it doesn't overload the channel circuitry, a process known as "maximising the dynamic range" or "setting the best signal to noise ratio". Note that the gain control does not boost or turn up the signal, it only determines how much of the signal will pass.
All equipment has dynamic range. This is the range between the quietest and loudest signals it can accommodate, or between the noise floor (beneath which a sound cannot be heard) and distortion. A signal entering a mixer needs to be as loud as possible without overloading the circuitry and causing distortion.
All circuits produce a fixed level of noise (hiss). If the source signal is loud enough this noise will be less noticeable.
Here's the method I use ...