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resistors: the braking resistors of electric trains, used to dissipate electrical power when the catenary is not receptive during braking, can make electromagnetically induced acoustic noise; coils: in magnetic resonance imaging, "coil noise" is that part of total system noise attributed to the receiving coil, due to its non-zero temperature.
Light buzzing can happen with plug-in and hardwired fixtures, so your lamp or chandelier could be the culprit. Luckily, that low-pitched sound wedging right between your ears is often the result ...
Digital audio is now common and may be transmitted via USB sound cards, USB headphones, Bluetooth, display connectors with integrated sound (e.g. DisplayPort and HDMI). Digital devices may also have internal speakers and mics. Thus the phone connector is sometimes considered redundant and a waste of space, particularly on thinner mobile devices.
Mains hum, electric hum, cycle hum, or power line hum is a sound associated with alternating current which is twice the frequency of the mains electricity.The fundamental frequency of this sound is usually double that of fundamental 50/60 Hz, i.e., 100/120 Hz, depending on the local power-line frequency.
A 1973 report cites a university study of fifty cases of people complaining about a "low throbbing background noise" that others were unable to hear. The sound, always peaking between 30 and 40 Hz (hertz), was found to only be heard during cool weather with a light breeze, and often early in the morning. These noises were often confined to a 10 ...
Many microphones operate at low voltage levels and some with high output impedance (hi-Z), which makes long microphone cables especially susceptible to electromagnetic interference. Microphone interconnections are therefore a common application for a balanced interconnection, which allows the receiver to reject most of this induced noise.
The noise level is proportional to the size of the device and the number of contacts. A small relay makes a soft click that may be difficult to hear. A large contactor makes a thud. I would not say that it is extremely loud, but you will certainly hear it if it is nearby and there is not a lot of other noise in the area.
An impulse noise filter can enhance the quality of noisy signals to achieve robustness in pattern recognition and adaptive control systems. A classic filter used to remove impulse noise is the median filter, at the expense of signal degradation. Thus it's quite common to get better performing impulse noise filters with model-based systems ...