minispec.core.stft

minispec.core.stft(y, n_fft=2048, hop_length=None, win_length=None, window='hann', center=True, dtype=<class 'numpy.complex64'>, pad_mode='reflect')[source]

Short-time Fourier transform (STFT)

Returns a complex-valued matrix D such that

np.abs(D[f, t]) is the magnitude of frequency bin f at frame t

np.angle(D[f, t]) is the phase of frequency bin f at frame t

Parameters:
y : np.ndarray [shape=(n,)], real-valued

the input signal (audio time series)

n_fft : int > 0 [scalar]

FFT window size

hop_length : int > 0 [scalar]

number audio of frames between STFT columns. If unspecified, defaults win_length / 4.

win_length : int <= n_fft [scalar]

Each frame of audio is windowed by window(). The window will be of length win_length and then padded with zeros to match n_fft.

If unspecified, defaults to win_length = n_fft.

window : string, tuple, number, function, or np.ndarray [shape=(n_fft,)]
  • a window specification (string, tuple, or number); see scipy.signal.get_window
  • a window function, such as scipy.signal.hanning
  • a vector or array of length n_fft
center : boolean
  • If True, the signal y is padded so that frame D[:, t] is centered at y[t * hop_length].
  • If False, then D[:, t] begins at y[t * hop_length]
dtype : numeric type

Complex numeric type for D. Default is 64-bit complex.

pad_mode : string

If center=True, the padding mode to use at the edges of the signal. By default, STFT uses reflection padding.
Returns:
D : np.ndarray [shape=(1 + n_fft/2, t), dtype=dtype]

STFT matrix

See also

istft
Inverse STFT
ifgram
Instantaneous frequency spectrogram
np.pad
array padding

Examples

>>> y, sr = minispec.load(minispec.util.example_audio_file())
>>> D = np.abs(minispec.stft(y))
>>> D
array([[2.58028018e-03, 4.32422794e-02, 6.61255598e-01, ...,
        6.82710262e-04, 2.51654536e-04, 7.23036574e-05],
       [2.49403086e-03, 5.15930466e-02, 6.00107312e-01, ...,
        3.48026224e-04, 2.35853557e-04, 7.54836728e-05],
       [7.82410789e-04, 1.05394892e-01, 4.37517226e-01, ...,
        6.29352580e-04, 3.38571583e-04, 8.38094638e-05],
       ...,
       [9.48568513e-08, 4.74725084e-07, 1.50052492e-05, ...,
        1.85637656e-08, 2.89708542e-08, 5.74304337e-09],
       [1.25165826e-07, 8.58259284e-07, 1.11157215e-05, ...,
        3.49099771e-08, 3.11740926e-08, 5.29926236e-09],
       [1.70630571e-07, 8.92518756e-07, 1.23656537e-05, ...,
        5.33256745e-08, 3.33264900e-08, 5.13272980e-09]], dtype=float32)

Use left-aligned frames, instead of centered frames

>>> D_left = np.abs(minispec.stft(y, center=False))

Use a shorter hop length

>>> D_short = np.abs(minispec.stft(y, hop_length=64))

Display a spectrogram

>>> import matplotlib.pyplot as plt
>>> minispec.display.specshow(minispec.amplitude_to_db(D,
...                                                  ref=np.max),
...                          y_axis='log', x_axis='time')
>>> plt.title('Power spectrogram')
>>> plt.colorbar(format='%+2.0f dB')
>>> plt.tight_layout()