Frequency response

From Includipedia, the inclusionist encyclopedia

Frequency response is the measure of any system's response at the output to a signal of varying frequency (but constant amplitude) at its input. In the audible range it usually referred to in connection with Electronic amplifiers, microphones and loudspeakers. Radio spectrum frequency response can refer to measurements of coaxial cables, category cables, video switchers and wireless communications devices. Subsonic frequency response measurements can include earthquakes and electroencephalography (brain waves).

The frequency response is typically characterized by the magnitude of the system's response, measured in dB, and the phase, measured in radians, versus frequency. The frequency response of a system can be measured by:

• applying an impulse to the system and measuring its response (see impulse response)
• sweeping a constant-amplitude pure tone through the bandwidth of interest and measuring the output level and phase shift relative to the input
• applying a signal with a wide frequency spectrum (e.g., maximum length sequence, white noise, or pink noise), and calculating the impulse response by deconvolution of this input signal and the output signal of the system.
• simply measuring the output of a system where an input signal isn't practical.

Once a frequency response has been measured (e.g., as an impulse response), providing the system is linear and time-invariant, its characteristic can be approximated with arbitrary accuracy by a digital filter. Similarly, if a system is demonstrated to have a poor frequency response, a digital or analog filter can be applied to the signals prior to their reproduction to compensate for these deficiencies.

Frequency response curves are often used to indicate the accuracy of amplifiers and speakers for reproducing audio. As an example, a high fidelity amplifier may be said to have a frequency response of 20 Hz - 20,000 Hz ±1 dB. This means that the system amplifies all frequencies within that range within the limits quoted. 'Good frequency response' therefore does not guarantee a specific fidelity, but only indicates that a piece of equipment meets the basic frequency response requirements.

See also

• Transfer function
• Bode plot
• Bandwidth
• Audio system measurements
• Transient response & steady-state response

es:Respuesta en frecuencia ja:周波数特性 ko:주파수 응답 it:Risposta in frequenza pt:Resposta em freqüência ru:Частотный отклик uk:Амплітудно-частотна характеристика zh:频率响应