A Constant Q Transform based on GWpy qtransform

The creation of this program was inspired by the need to include a CQT package with minimal size and dependency for SHARCNET (ComputeCanada) Supercomputer Clusters.

​x
# IMPORTANT DISCLAIMER: All credits for the original Q transform algorithm go to the authors of *GWpy* and *Omega* pipeline.
# See original algorithms at: [Omega Scan] https://gwdetchar.readthedocs.io/en/stable/omega/
#                             [GWpy] https://gwpy.github.io/docs/stable/
#          particularly       [GWpy qtransform]
#              - https://github.com/gwpy/gwpy/blob/26f63684db17104c5d552c30cdf01248b2ec76c9/gwpy/signal/qtransform.py
#
# The license information does NOT imply this package (constantQ) as the original q transform/q scan algorithm.
# NOTE: Referenced programs are under the GNU license 
# for more information on the license visit: https://www.gnu.org/licenses/gpl-faq.en.html

How to use it:

Step 1: Generating a chirp signal

x
import numpy as np
​
# Generate np.array chirp signal
dt = 0.001
t = np.arange(0,3,dt)
f0 = 50
f1 = 250
t1 = 2
x = np.cos(2*np.pi*t*(f0 + (f1 - f0)*np.power(t, 2)/(3*t1**2)))
fs = 1/dt
​
plt.plot(x)             # plot the chirp signal
plt.show()              # display

Step 2: Generating a TimeSeries object

x
from constantQ.timeseries import TimeSeries
series = TimeSeries(x, dt = 0.001, unit='m', name='test', t0=0)     #np.array --> constantQ.timeseries    

Step 3: Q Transform

x
hdata = series
sq = hdata.q_transform(search=None)             # q transform
print(len(sq[0]))       # freq array length
print(len(sq))          # time array length
​
plt.imshow(sq.T, origin='lower')                # plot the spectrogram
plt.colorbar()                                  # colorbar
plt.show()                                      # display

To compare the result with a Scipy Spectrogram

x
from scipy import signal as scisignal
​
freq, ts, Sxx = scisignal.spectrogram(x)        # scipy spectrogram
​
plt.pcolor(ts, freq, Sxx, shading='auto')       # plot the spectrogram
plt.colorbar()                                  # colorbar
plt.show()                                      # display

This test version 0.0.1 largely follows the GWpy architecture. Changes will be made in future updates if a different structure is better for this package.