Distortion

Frequency Distortion. This is defined¹ as "that form of distortion in which the change is in the relative magnitudes of the different frequency components of a wave, provided that the change is not caused by non-linear distortion." Thus, if the transmitting efficiency of a circuit or piece of equipment is different at various frequencies, frequency distortion results. This is sometimes called amplitude distortion.

Non-Linear Distortion. This is defined¹ as "that form of distortion which occurs when the ratio of voltage to current, using root-mean-square values (or analogous quantities in other fields), is a function of the magnitude of either." Non-linear distortion causes harmonics to be created (see page 558). If a pure sine-wave voltage is impressed on a circuit (such as an iron-cored transformer) having a non-linear impedance (ratio of voltage to current as just defined), the current that flows will not be a pure sine wave, but will contain harmonics and will be irregular in shape. Non-linear circuits have many useful applications in communication, such as modulation (page 420), demodulation (page 421), and the generation of carrier frequencies (page 425).

Delay Distortion. This is defined¹ as "that form of distortion which occurs when the phase angle of the transfer impedance (page 423) with respect to two chosen pairs of terminals is not linear with frequency within a desired range, thus making the time of transmission or delay vary with frequency in that range." Delay distortion is the type of distortion that occurs when the velocity of propagation or speed of transmission of a wave through a circuit varies with the frequency of the wave. Considerable delay distortion is tolerable in the transmission of speech and music but is very objectionable in picture and television transmission.