Skip to main content
`Ctrl`+`K`
scipy.signal.

# group_delay

scipy.signal.group_delay(system, w=512, whole=False, fs=6.283185307179586)

  Compute the group delay of a digital filter.

  The group delay measures by how many samples amplitude envelopes of various spectral components of a signal are delayed by a filter. It is formally defined as the derivative of continuous (unwrapped) phase:

                d        jw
      D(w) = - -- arg H(e)
               dw

  Parameters:
    system tuple of array_like (b, a)

      Numerator and denominator coefficients of a filter transfer function.

    w{None, int, array_like}, optional

      If a single integer, then compute at that many frequencies (default is N=512).

      If an array_like, compute the delay at the frequencies given. These are in the same units as fs.

    whole bool, optional

      Normally, frequencies are computed from 0 to the Nyquist frequency, fs/2 (upper-half of unit-circle). If whole is True, compute frequencies from 0 to fs. Ignored if w is array_like.

    fs float, optional

      The sampling frequency of the digital system. Defaults to 2*pi radians/sample (so w is from 0 to pi).

      Added in version 1.2.0.

  Returns:
    w ndarray

      The frequencies at which group delay was computed, in the same units as fs. By default, w is normalized to the range [0, pi) (radians/sample).

    gd ndarray

      The group delay.

  See also

  `freqz`

    Frequency response of a digital filter

  Notes

  The similar function in MATLAB is called grpdelay.

  If the transfer function \(H(z)\) has zeros or poles on the unit circle, the group delay at corresponding frequencies is undefined. When such a case arises the warning is raised and the group delay is set to 0 at those frequencies.

  For the details of numerical computation of the group delay refer to [1] or [2].

  Added in version 0.16.0.

  References

  [1]

  Richard G. Lyons, “Understanding Digital Signal Processing, 3rd edition”, p. 830.

  [2]

  Julius O. Smith III, “Numerical Computation of Group Delay”, in “Introduction to Digital Filters with Audio Applications”, online book, 2007, https://ccrma.stanford.edu/~jos/fp/Numerical_Computation_Group_Delay.html

  Examples

      >>> from scipy import signal
      >>> b, a = signal.iirdesign(0.1, 0.3, 5, 50, ftype='cheby1')
      >>> w, gd = signal.group_delay((b, a))

      >>> import matplotlib.pyplot as plt
      >>> plt.title('Digital filter group delay')
      >>> plt.plot(w, gd)
      >>> plt.ylabel('Group delay [samples]')
      >>> plt.xlabel('Frequency [rad/sample]')
      >>> plt.show()