The recording chain, set up by various electroacoustic devices like microphones , amplifiers or digital filters, may be seen as a single ``black box '' with a single input and single output. This is commonly called a system. A recording channel is a transmission channel between the signal to be recorded and the recording medium (i.e. analogue or digital tape recorder, hard disk). In the cases of one, two and more channels we speak of monophonic, stereophonic and multi-channel recordings , respectively.
The effects of using arbitrary recording system are twofold. First, the signal sent from the input through the system to its output is altered compared to the intended, but ideal, transformation in amplitude and/or delay time. Since ideal systems are to be found in theory only, unwanted side effects (distortions) due to a deviation of system behaviour from the ideal specification have to be considered.
The second kind of system characteristics are discussed below. Although these characteristics are not desired, it is important not to neglect them, either when choosing a specific device or in reporting a system configuration. For that reason, all manuals of the system components under consideration should be checked for the relevant distortion data.