Classe « Axes »

Méthode matplotlib.figure.Axes.specgram

Signature de la méthode specgram

def specgram(self, x, NFFT=None, Fs=None, Fc=None, detrend=None, window=None, noverlap=None, cmap=None, xextent=None, pad_to=None, sides=None, scale_by_freq=None, mode=None, scale=None, vmin=None, vmax=None, *, data=None, **kwargs) 

Description

specgram.__doc__

Plot a spectrogram.

Compute and plot a spectrogram of data in *x*.  Data are split into
*NFFT* length segments and the spectrum of each section is
computed.  The windowing function *window* is applied to each
segment, and the amount of overlap of each segment is
specified with *noverlap*. The spectrogram is plotted as a colormap
(using imshow).

Parameters
----------
x : 1-D array or sequence
    Array or sequence containing the data.

Fs : float, default: 2
    The sampling frequency (samples per time unit).  It is used to calculate
    the Fourier frequencies, *freqs*, in cycles per time unit.

window : callable or ndarray, default: `.window_hanning`
    A function or a vector of length *NFFT*.  To create window vectors see
    `.window_hanning`, `.window_none`, `numpy.blackman`, `numpy.hamming`,
    `numpy.bartlett`, `scipy.signal`, `scipy.signal.get_window`, etc.  If a
    function is passed as the argument, it must take a data segment as an
    argument and return the windowed version of the segment.

sides : {'default', 'onesided', 'twosided'}, optional
    Which sides of the spectrum to return. 'default' is one-sided for real
    data and two-sided for complex data. 'onesided' forces the return of a
    one-sided spectrum, while 'twosided' forces two-sided.

pad_to : int, optional
    The number of points to which the data segment is padded when performing
    the FFT.  This can be different from *NFFT*, which specifies the number
    of data points used.  While not increasing the actual resolution of the
    spectrum (the minimum distance between resolvable peaks), this can give
    more points in the plot, allowing for more detail. This corresponds to
    the *n* parameter in the call to fft(). The default is None, which sets
    *pad_to* equal to *NFFT*

NFFT : int, default: 256
    The number of data points used in each block for the FFT.  A power 2 is
    most efficient.  This should *NOT* be used to get zero padding, or the
    scaling of the result will be incorrect; use *pad_to* for this instead.

detrend : {'none', 'mean', 'linear'} or callable, default: 'none'
    The function applied to each segment before fft-ing, designed to remove
    the mean or linear trend.  Unlike in MATLAB, where the *detrend* parameter
    is a vector, in Matplotlib is it a function.  The :mod:`~matplotlib.mlab`
    module defines `.detrend_none`, `.detrend_mean`, and `.detrend_linear`,
    but you can use a custom function as well.  You can also use a string to
    choose one of the functions: 'none' calls `.detrend_none`. 'mean' calls
    `.detrend_mean`. 'linear' calls `.detrend_linear`.

scale_by_freq : bool, default: True
    Whether the resulting density values should be scaled by the scaling
    frequency, which gives density in units of Hz^-1.  This allows for
    integration over the returned frequency values.  The default is True for
    MATLAB compatibility.

mode : {'default', 'psd', 'magnitude', 'angle', 'phase'}
    What sort of spectrum to use.  Default is 'psd', which takes the
    power spectral density.  'magnitude' returns the magnitude
    spectrum.  'angle' returns the phase spectrum without unwrapping.
    'phase' returns the phase spectrum with unwrapping.

noverlap : int, default: 128
    The number of points of overlap between blocks.

scale : {'default', 'linear', 'dB'}
    The scaling of the values in the *spec*.  'linear' is no scaling.
    'dB' returns the values in dB scale.  When *mode* is 'psd',
    this is dB power (10 * log10).  Otherwise this is dB amplitude
    (20 * log10). 'default' is 'dB' if *mode* is 'psd' or
    'magnitude' and 'linear' otherwise.  This must be 'linear'
    if *mode* is 'angle' or 'phase'.

Fc : int, default: 0
    The center frequency of *x*, which offsets the x extents of the
    plot to reflect the frequency range used when a signal is acquired
    and then filtered and downsampled to baseband.

cmap : `.Colormap`, default: :rc:`image.cmap`

xextent : *None* or (xmin, xmax)
    The image extent along the x-axis. The default sets *xmin* to the
    left border of the first bin (*spectrum* column) and *xmax* to the
    right border of the last bin. Note that for *noverlap>0* the width
    of the bins is smaller than those of the segments.

**kwargs
    Additional keyword arguments are passed on to `~.axes.Axes.imshow`
    which makes the specgram image. The origin keyword argument
    is not supported.

Returns
-------
spectrum : 2D array
    Columns are the periodograms of successive segments.

freqs : 1-D array
    The frequencies corresponding to the rows in *spectrum*.

t : 1-D array
    The times corresponding to midpoints of segments (i.e., the columns
    in *spectrum*).

im : `.AxesImage`
    The image created by imshow containing the spectrogram.

See Also
--------
psd
    Differs in the default overlap; in returning the mean of the
    segment periodograms; in not returning times; and in generating a
    line plot instead of colormap.
magnitude_spectrum
    A single spectrum, similar to having a single segment when *mode*
    is 'magnitude'. Plots a line instead of a colormap.
angle_spectrum
    A single spectrum, similar to having a single segment when *mode*
    is 'angle'. Plots a line instead of a colormap.
phase_spectrum
    A single spectrum, similar to having a single segment when *mode*
    is 'phase'. Plots a line instead of a colormap.

Notes
-----
The parameters *detrend* and *scale_by_freq* do only apply when *mode*
is set to 'psd'.

.. note::
    In addition to the above described arguments, this function can take
    a *data* keyword argument. If such a *data* argument is given,
    the following arguments can also be string ``s``, which is
    interpreted as ``data[s]`` (unless this raises an exception):
    *x*.

    Objects passed as **data** must support item access (``data[s]``) and
    membership test (``s in data``).