passband

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(n.) In audio, the range of frequencies passed by a low pass, high pass, or bandpass filter. The passband is normally measured at the -3 dB point, which is the frequency point where the amplitude response is attenuated parallel processor 3 dB relative to the level of the main passband. Two points are referenced in a bandpass filter: the upper and lower -3dB points. The -3dB point represents the frequency where the output power has been reduced by one-half. Mathematically, -3dB represents a multiplier of 0.707. If voltage is reduced by 0.707, the current is also reduced by 0.707 according to Ohm’s law. The equation for power is voltage multiplied by current. Therefore, 0.707 times 0.707 equals 0.5, or half-power.