Bandwidth

  Defines the part of the frequency spectrum where the attenuation through a device is low, thus allowing a uniform transfer of the signals within that band (passband). Usually measured at the half-power points of the response curve i.e the points of -3 dB ( Decibel).

For communication purposes, the bandwidth defines the amount of information that can be transferred through a particular channel in a given time interval. For analogue signals, the bandwidth defines the quality of the channel. Typical values are 3000 Hz for speech and 15 to 20 KHz for high-quality channels. In the case of digital transmission, the bandwidth defines the maximum information capacity, baud, of the channel.

The bandwidth can either be referred to an interval starting at 0 Hz (baseband) or to any other part of the spectrum. Baseband information can be modulated, by various methods, on a high frequency carrier. Note that after modulation, the bandwidth required to transfer the baseband information might increase.

Bandwidth limiting is often applied to readout electronics of sensors, in order to optimize the signal-to-noise ratio (``shaping'').