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SSML definition of "semitone"

From: Daniel Weck <daniel.weck@gmail.com>
Date: Thu, 14 Jul 2011 19:49:33 +0100
Message-Id: <28C2AA75-9B33-4391-8070-8D149FE6A454@gmail.com>
Cc: Alan Gresley <alan@css-class.com>
To: www-voice@w3.org, dburnett@voxeo.com
Dear all,

The draft of the CSS Speech Module used to provide the same description of a "semitone" as the one found in the SSML Recommendation (verbatim copy):

A semitone is half of a tone (a half step) on the standard diatonic scale.

Following a remark on the CSS public mailing list [1] that this is at worst an incorrect definition, and at best a misleading/confusing statement, we have decided to rephrase this part of the prose (a diatonic scale combines semitone and full-tone intervals, so "a half step" isn't normatively relevant). Here is the current proposal, your feedback is welcome:

A semitone interval corresponds to the step between each note on an equal temperament chromatic scale. A semitone can therefore be quantified as the difference between two consecutive pitch frequencies on such scale. The ratio between two consecutive frequencies separated by exactly one semitone is the twelfth root of two (approximately 1.05946). As a result, the value in Hertz corresponding to a semitone offset is relative to the initial frequency the offset is applied to (in other words, a semitone doesn't correspond to a fixed numerical value in Hertz).

Regards, Daniel

Received on Thursday, 14 July 2011 18:50:05 UTC

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