am_sine_generator

am_sine_generator(xmod, fs, fc, spl_level, print_m=False)

Amplitude-modulated sine wave generation

This function creates an amplitude-modulated (AM) signal with sinusoidal carrier of frequency ‘fc’, and arbitrary modulating signal ‘xmod’. The AM signal length is the same as the length of ‘xmod’. The signal level is adjusted to ‘spl_level’ in dB.

Parameters:

• xmod (array) – Modulating signal, dim(N).

• fs (float) – Sampling frequency, in Hz.

• fc (float) – Carrier frequency, in Hz. Must be less than ‘fs/2’.

• spl_level (float) – Sound Pressure Level [dB ref 20 uPa RMS] of the modulated signal.

• print_m (bool, optional) – Flag declaring whether to print the calculated modulation index. Default is False.

Returns:

• y (numpy.array) – Amplitude-modulated signal with sine carrier in Pascals, dim(N).

• m (float) – Modulation index

Warning

spl_level must be provided in dB, ref=2e-5 Pa.

See also

am_noise_generator

Amplitude modulation with broadband noise carrier

fm_sine_generator

Frequency modulation with sine wave carrier

sine_wave_generator

Sine wave generation

Notes

The modulation index ‘m’ will be equal to the peak value of the modulating signal ‘xmod’. Its value can be printed by setting the optional flag ‘print_m’ to True.

For ‘m’ = 0.5, the carrier amplitude varies by 50% above and below its unmodulated level. For ‘m’ = 1.0, it varies by 100%. With 100% modulation the wave amplitude sometimes reaches zero, and this represents full modulation. Increasing the modulating signal beyond that point is known as overmodulation.

Examples

>>> from mosqito.utils import am_sine_generator
>>> import matplotlib.pyplot as plt
>>> import numpy as np
>>> fs = 48000      # [Hz]
>>> duration = 1
>>> t = np.linspace(0, duration, int(fs*duration))
>>> dB = 60         # [dB SPL]
>>> fc = 100        # [Hz]
>>> fm = 4          # [Hz]
>>> xmod = np.sin(2*np.pi*t*fm)
>>> y_am, m = am_sine_generator(xmod, fs, fc, dB, True)
>>> fig, plots = plt.subplots(2, 1)
>>> plots[0].set_title(f'Amplitude-modulated sine wave, modulation index = {m:.1f}')
>>> plots[0].plot(t, xmod, 'C0', label='Modulating signal')
>>> plots[0].legend(loc='upper right')
>>> plots[0].grid()
>>> plots[0].set_ylabel('Amplitude')
>>> plots[0].set_xlim([0, duration])
>>> plots[1].plot(t, y_am, '#69c3c5', label='AM signal')
>>> plots[1].legend(loc='upper right')
>>> plots[1].grid()
>>> plots[1].set_ylabel('Amplitude')
>>> plots[1].set_xlim([0, duration])
>>> plots[1].set_xlabel('Time [s]')
>>> fig.set_tight_layout('tight')
>>>

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