This illusion was also discovered by Deutsch (1986). In music, tritone refers to the half octave, or the interval spanning six semitones. Thus, in the key of C major, there is one tritone: If you start on F, you can go up six semitones to B. Similarly, E and A-sharp are tritones (see Figure 13.21). In the tritone paradox, Deutsch presents stimuli generated similar to the way Shepard generated his paradoxical scale, that is, each note is an envelope of sound sweeping from one octave to the next, but with a heard pitch equivalent to the lower note. Thus, in the tritone paradox, Deutsch played a note with a perceived pitch of C and one with a perceived pitch of F-sharp, a tritone away. Here’s the paradox: Some people hear the notes as ascending, as in a lower C to a higher F-sharp, whereas other people hear the notes descending, as in a higher C to a lower F-sharp.
In this illustration, you can play the tritones and see which whay you hear the tones move. It is good play this in a group to see if you all agree.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
Below is a list of the ways that you can alter the illustration. The settings include the following:
Play: start play a pair of tones to experience the tritone paradox.
Keyboard: click or touch a key to play the tone associated with that key. See if other intervals suffer the same illusion?
Lower Note: what note will be the lower tone of the pair to play.
Interval: what musical interval will be played between the two tones: a fourth, a tritone, or a fifth.
Tone Type: play a Paradox Tone or just the Fundamental of the paradoxical done.
Plot Frequency: You can have the frequency graph plotted Linearly where each Hertz step is the same size or Logarithmically where the ratio between given frequencies stays the same size.
Pressing this button restores the settings to their default values.