Sampling frequency
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Signal Processing and Control Theory
In digital signal processing and in control theory, sampling frequency is the rate at which a continuous-time (analog) signal is sampled into a discrete-time (digital) signal consisting of digital samples. Sampling frequency is usually measured in hertz, or samples per second.
The sample time of a discrete signal can refer either to the period of samples taken from that signal or to the time that a particular sample was taken. In the first case, it is the inverse of the sample rate.
When converting from analog to digital, the analog signal must usually be sampled -- that is, measured or read -- at discrete intervals of time. The length of the interval depends on the application, but is limited by the Nyquist-Shannon sampling theorem. The sampling frequency is the inverse of this number: the smaller the interval, the higher the frequency, and, in general, higher frequencies imply higher-quality sampling.
Audio
In digital audio, common sampling rates are:
- 8000 Hz - telephone, adequate for human speech
- 11025 Hz
- 22050 Hz - radio
- 44100 Hz - compact disc
- 48000 Hz - digital sound used for films and professional audio
- 96000 or 192400 Hz - DVD Audio and Super ACD (
Video
In digital video, which uses a CCD as the sensor, the sampling rate is defined the frame/field rate, rather than the notional pixel clock. All modern TV cameras use CCDs, and the image sampling frequency is the repetition rate of the CCD integration period.
When analogue video is converted to digital video, a different sampling process occurs, this time at the pixel frequency. Some common pixel sampling rates are:
- 13.5 MHz - CCIR 601, D1 video
See Also
de:Samplingfrequenz nl:bemonsteringsfrequentie ja:サンプリング周波数
