Let's take a quick look at level calibration. We've explored the different paths an audio signal takes in a recording studio, from one piece of equipment to another (for example: microphone --> mixer --> recorder --> mixer again --> effect --> effect return --> mixer again etc., this is also known as signal flow). It is of paramount importance for the output levels of a module to be compatible with the input levels of the module that follows it. That's why we have certain potentiometers, named trimmers that are usually located inside the machines, which need to be calibrated when the studio is being setup and checked-up regularly. Here is how calibration takes place: you use an oscillator (generally set at a frequency of 1 KHz) and you adjust all the equipment's level in such a way that all the outputs and all the inputs are at a standard level of 0 Vu [Standard Operating Level ] . This way we are sure that the levels are the same throughout the whole recording studio.