shannon-nyquist theorem

One can recover a continuous signal xc(t) from sampled signal x[n] exactly when

1. xc(t) is a bandlimited signal

2. The sampling rate is greater than twice the frequency, or

   2πT>2Ωmax

   Where T is the sampling period (how long between samples) and Ωmax is the maximum frequency in the frequency response of xc(t)