In Indo-European languages, changing the pitch of the voice usually does not change the meaning of a spoken word or sentence. We illustrate this here, using as our speech sample one of the finer samples of political rhetoric of the early 3rd millennium. (No, not Obama, Bush. Dubya asserting that peace with fish is possible, which is of course enormously reassuring.) In addition to the original speech sample, we add two further samples which have been processed with Hideki Hawakara's "Straight" software, which can decompose speech into its pitch and formant contours, and resynthesize it after the pitch contour has been altered. The result sounds remarkably realistic. So here, then, is Bush, pleading for peace with fish, first normal, then with a steadily rising, and then with a falling pitch contour. You will note that, after the pitch manipulation, the speech remains comprehensible (at least, it is no less comprehensible than it was on the outset).
Bush pleads peace with fish. (Original pitch contour, varying between about 110 and 200 Hz)
Bush pleads peace with fish, rising pitch. (Steady, linear rise from 80 to 350 Hz)
Bush pleads peace with fish, falling pitch. (Steady, linear fall from 350 to 80 Hz)
In the examples above we manipulated the pitch of the speech to rise or fall over a widerange, which had no appreciable effect on how comprehensible the sentences are. This may create the impression that voice pitch is unimportant in spoken English, but that would be only partly true. While in English, voice pitch has no "semantic" role, it is a key feature of "prosody", which can, for example, give us non-verbal cues to a speaker's intent or affect. To illustrate this, consider the next two examples where we took the pitch contour of the original recording, and then either halved or doubled the range of the pitch variation. When the pitch range is halved, the voice sounds markedly depressed, when it is doubled it sounds very excited.
Bush depressed. (Normal pitch contour compressed from normal 110 - 200 Hz range to a much smaller 110-120 Hz range)
Bush excited. (Normal pitch contour expanded from normal 110 - 200 Hz range to a much larger 50-350 Hz range)