You went to the simple image wikipedia just to find a citation that agrees with you, while the english Wikipedia has a whole artcicle describing it in quite an

You went to the simple image wikipedia just to find a citation that agrees with you, while the english Wikipedia has a whole artcicle describing it in quite an opposite way: https://en.wikipedia.org/wiki/Audio_signal https://en.wikipedia.org/wiki/Audio_signal If it is confusing, is because you do not understand what a "signal" means. A signal is not the phenomenon itself, it is a representation of it. An audio signal is a signal that represents sound, but it is not sound itself. If it were, you would not need to call it a signal, it would be simply "sound". In a slightly different use of adjective, an acoustic signal is a signal (that may or not be audio, eg, ultrassound) that is carried by sound waves. Actually, it only gets confusing if you try to be pedantic, as GP did. Everyone knows what an audio signal in a EM chart.