Creating a sound synthesizer in the notebook

In this recipe, we will create a small electronic piano in the notebook. We will synthesize sinusoidal sounds with NumPy instead of using recorded tones.

How to do it...

1. We import the modules:

   In [1]: import numpy as np
           import matplotlib.pyplot as plt
           from IPython.display import (Audio, display,
                                        clear_output)
           from IPython.html import widgets
           from functools import partial
           %matplotlib inline

2. We define the sampling rate and the duration of the notes:

   In [2]: rate = 16000.
           duration = 0.5
           t = np.linspace(0., duration, rate * duration)

3. We create a function that generates and plays the sound of a note (sine function) at a given frequency, using NumPy and IPython's Audio class:

   In [3]: def synth(f):
               x = np.sin(f * 2. * np.pi * t)
               display(Audio(x, rate=rate, autoplay=True))

4. Here is the fundamental 440 Hz note:

   In [4]: synth(440)

5. Now, we generate the...