When no specific feature is to be observed in sound, the best way to represent it is to display its spectrogram since it reflects what the ear does: measuring energy among frequencies as its varies with time.
You can get that representation using the free and open source command-line tool SoX:
sox sound-original.wav -n spectrogram -o sound-original.png
sox sound-altered.wav -n spectrogram -o sound-altered.png
The alterations in the second sound can clearly be seen on its spectrogram which is good.
But in the case of more subtle alterations, it could be difficulty to see them.
In such a case, computing the difference between the two signals and displaying its spectrogram would be appropriate:
sox -m -v 1 sound-original.wav -v -1 sound-altered.wav sound-difference.wav
sox sound-difference.wav -n spectrogram -o sound-difference.png
Alternatively, creating the spectrogram directly without writing a temporary file:
sox -m -v 1 sound-original.wav -v -1 sound-altered.wav -n spectrogram -o sound-difference.png
In the command above,
-m asks SoX to mix audio files together, and
-v is intended to change the volume by a linear factor.
In our case, the volume of
sound-original.wav is left unchanged, whereas the
-1 factor applied to
sound-altered.wav is used to invert it.
The whole command computes the difference between the two audio signals.