The resulting sound quality from a microphone depends on many factors: the class of the microphone itself, the characteristics of amplifying devices, communication cables, etc. But often, even with the perfect selection and adjustment of all components, the sound is unsatisfactory. Because the microphone is phoning.
The mechanisms behind the background noise effect when using a microphone can vary. In most cases, the reasons for this phenomenon lie not so much in the microphone itself as in the intermediate electrical circuits and devices through which the audio signal passes. … In this case, the background is due to the occurrence of an induced voltage comparable in amplitude to the microphone signal from household lighting networks. The background frequency, respectively, is equal to the frequency of the mains voltage (in Russia - 50 Hz). In order to avoid this problem, you need to use a braided cable to connect the microphone. The braid of the cable must be connected to the "case" (zero supply circuit) of the amplifier. The hum caused by interference from household electrical networks can also occur when using a shielded cable. Often, the background only appears when you touch the housing or individual metal parts of the microphone housing. This means that the signal core of the cable is galvanically connected to these parts. The background signal is induced in the human body and, upon contact with a microphone, is transmitted to the input of the amplifier. The source of interference can also be various household devices, for example, mobile phones. Often, such a background does not appear constantly, but in periods of varying duration (when certain subsystems of devices are operating). Induced electrical oscillations of the audible frequency range, as a rule, are a multiple of the harmonic of the original high-frequency signal or the result of the separation of its low-frequency component on the filter formed by parasitic inductance and the capacitance of the cable to which the microphone is connected.
