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TriTone paradox

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The tritone paradox is an auditory illusion in which a sequentially played pair of Shepard tones separated by an interval of a tritone, or half octave, is heard as ascending by some people and as descending by others. Different populations tend to favor one of a limited set of different spots around the chromatic circle as central to the set of "higher" tones. The tritone paradox was first reported by psychology of music researcher Diana Deutsch in 1986.
 


Each Shepard tone consists of a set of octave related sinusoids, whose amplitudes are scaled by a fixed bell shaped spectral envelope based on a log frequency scale. For example, one tone might consist of a sinusoid at 440 Hz, accompanied by sinusoid at the higher octaves (880 Hz, 1760 Hz, etc.) and lower octaves (220 Hz, 110 Hz, etc.). The other tone might consist of a 311 Hz sinusoid, again accompanied by higher and lower octaves (622 Hz, 155.5 Hz, etc.). The amplitudes of the sinusoids of both complexes are determined by the same fixed amplitude envelope - for example the envelope might be centered at 370 Hz and span a 6 octave range.
 


Shepard predicted that the two tones would constitute a bistable figure, the auditory equivalent of the Necker cube, that could be heard ascending or descending, but never both at the same time. Diana Deutsch later found that perception of which tone was higher depended on the absolute frequencies involved: an individual will usually find the same tone to be higher, and this is determined by the tones' absolute pitches. This is consistently done by a large portion of the population, despite the fact that responding to different tones in different ways must involve the ability to hear absolute pitch, which was thought to be extremely rare. This finding has been used to argue that latent absolute-pitch ability is present in a large proportion of the population. In addition, Deutsch found that subjects from the south of England and from California resolved the ambiguity the opposite way. Also, Deutsch, Henthorn and Dolson found that native speakers of Vietnamese, a tonal language, heard the tritone paradox differently from Californians who were native speakers of English.
 
TriTone paradox example 

 



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I've read the text three times and I still cannot fathom what they're saying. Apparently, I'm THAT stupid.

 

I hear four groups of two tones with pause in between the pairings.

 

First two pairs are decending, high/low...high/low. With the second pair being lower than the first.

 

Second two pairs are acending, low/high...low/high. The final pair is higher than the third.

 

The more I listen to this, the more ambiguous the third pair is. It was quite clear to me (low/high) the first time.

 

My wife hears all four pairs as high/low.

 

 

 

 

 

For the record, I have a floppy vinyl record that was included in one of the Audio magazines, they did an article on Diana Deutsch. The floppy vinyl record is "Audible Illusions for Headphones".
 
 
I've also got a CD "Auditory Demonstrations" by Houtsma, Rossing, and Wagenaars.  "Prepared at the Institute for Perception Research (IPO), Eindoven, The Netherlands.  Supported by the Acoustical Society of America"  There's 80 tracks in 39 groups of auditory oddities like this.  Released by Philips, #1126-061.  Comes with a 90+ page booklet.
 
This CD-ROM has--I think--the same content as my CD.  This is sold by the Acoustical Society of America:

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 Putting together different auditory perceptions such as the one described here, makes me wonder how different subsets of these perceptions would influence our like or dislike of certain genres of music. Maybe to take it further, also what we like in a certain persons voice, or whether we like quiet places or not.

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 Putting together different auditory perceptions such as the one described here, makes me wonder how different subsets of these perceptions would influence our like or dislike of certain genres of music. Maybe to take it further, also what we like in a certain persons voice, or whether we like quiet places or not.
 
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