As we have seen, the effect of signal clipping on a sinusoid is primarily to produce harmonics al multiples of the sinusoidal frequency. These could casily be removed through the application of a low pass filter designed to pass frequencies lower than that of the sinusoid while rejecting the higher frequency harmonics. In this section, we will examine the effects of clipping on a trumpet signal. (a) Place the file trump_short. mat into your MATLAB workspace. This file can be downloaded from Black- board. Once the file is in your workspace, use the following MATLAB commands to retrieve an audio file of a trumpet >> load('trump_short. nat'); After you load this file, your workspace will contain the following two files: 1. trumpet 2. fs The file trumpet consists of a trumpet playing the note middle C, which is nominally 261.626 Hz. The variable is is the sampling rate which is 44.100 Hz. and the signal trumpet has been normalized to have a maximum absolute value of unity
(b) Use soundse to listen to the trumpet with the command: >> soundsc(trumpet, fs); le)
(c) Compute the spectrum of this signal using the method from part 3 (d) above. Plot this spectrum over the range 0 to 3,000 Hz. More than 10 harmonic peaks should be visible.
(d) Using the same approach as in Part 3 above, apply a clipping level of 0 to the trumpet signal and plot the resulting spectrum on the same plot as the original (un-clipped) signal. Comment on the differences that you observe in the spectra of the original and clipped trumpet signals. Again, use sounds to listen to the clipped trumpet waveform. le)
(e) Experiment with different clipping levels between 0 and 1. By varying the clipping level and listening to the result, find the lowest value of clipping detectable by car when you play the clipped waveform.