code: def new_note_track(env, synth):
    
    list_env = list(env)
    return chain.from_iterable(synth(freq) * list_env for freq in freq_gen())
docs: Audio track with the frequencies.
  
    Parameters
    ----------
    env:
      Envelope Stream (which imposes the duration).
    synth:
      One-argument function that receives a frequency (in rad/sample) and
      returns a Stream instance (a synthesized note).
  
    Returns
    -------
    Endless Stream instance that joins synthesized notes.