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# 6 What is the sampling and sample recovery?

(1) of the continuous signal such as the formation of the sampling interval sampling signal, sampling the signal spectrum is continuous spectrum with a sampling frequency of the signal cycle of the periodic extension form.

(2) the signal of the highest cutoff frequency fi, the sampling frequency f2, if the sampling frequency f2 2fi, then let the sampling signal through a cut-off frequency fi of the ideal low-pass filter, the summer can be uniquely recovered the original signal (which is the Nyquist sampling law), otherwise it will cause the sampled signal spectrum aliasing, it is impossible to restore the original signal without distortion.

but considering the actual sampling of the analog signal is not a sharp cutoff of the spectrum (an ideal rectangular characteristic), the highest top of the spectrum there are a number of smaller high-frequency components, it is generally f2 take 5fi ~ 10f1.

7. sampling frequency is too low what will happen? How to calculate the deviation? How to solve?

result of low sampling frequency of the signal to restore the original signal with different frequency. This signal distortion is called aliasing. Aliasing error occurs in the input signal sampling frequency of the closest integer multiple of the absolute difference.

example, the sampling frequency is 100 Hz, 510 HZ signal containing the ingredients, then the aliasing error is F = 15 100-510I = 10Hz.

To avoid this from happening, usually before the signal is collected through a low pass filter, the signal above the Nyquist frequency signal components filtered. This filter is called anti-aliasing filter.

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