Spectrograms.

Spectrograms Because sound is a transitory phenomenon and only able to be perceived subjectively by listeners, experimental phoneticians have several methods of making the sound permanent by displaying it in visual form. This makes objective measurement of phenomena within the soundwave possible, and removes the possibility of subjective error while making auditory judgements. The commonest visual display we have in experimental phonetics is called the sound spectrogram. The display takes the form of a graph …

…which a sound is coming toward us. Because of the difference in arrival time of a sound at our two separate ears we are able to compute the direction of the sound from the degree to which the two different signals (one from each ear) are out of phase (i.e. out of step with one another). It is, among other things, artificial manipulation of this parameter which makes stereophonic or binaural sound reproduction possible.