dgrad.py 文件源码

def differentiator(n, Hz=1):
    """
    Return linear phase impulse response for a length *n* filter that
    approximates the differential operator. The sampling frequency is
    *Hz*.

    The filter length *n* must be even. The remez function returns
    type 3 (for *n* odd) and 4 (for *n* even) linear phase
    filters. However, type 3 linear phase filters are 0 at $\omega =
    0$ and $\omega = \pi$.
    """
    if n % 2 == 1:
        raise ValueError('the filter length n must be even')
    return scipy.signal.remez(n,
                              [0, Hz / 2],
                              [1],
                              Hz=Hz,
                              type='differentiator') * Hz * 2 * NP.pi