code: def bisine_wave(frequency):
    
    #
    # We can first our existing sine generator to generate two different
    # waves.
    f_hi = frequency
    f_lo = frequency / 2.0
    with tf.name_scope('hi'):
      sine_hi = sine_wave(f_hi)
    with tf.name_scope('lo'):
      sine_lo = sine_wave(f_lo)
    #
    # Now, we have two tensors of shape [1, _samples(), 1]. By concatenating
    # them along axis 2, we get a tensor of shape [1, _samples(), 2]---a
    # stereo waveform.
    return tf.concat([sine_lo, sine_hi], axis=2)
docs: Emit two sine waves, in stereo at different octaves.