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Re: [css3-speech] voice-pitch

From: Daniel Weck <daniel.weck@gmail.com>
Date: Thu, 14 Jul 2011 18:12:26 +0100
Cc: fantasai <fantasai.lists@inkedblade.net>
Message-Id: <C4917FF2-6988-4B79-98BA-E0B61394B807@gmail.com>
To: www style <www-style@w3.org>, Alan Gresley <alan@css-class.com>
On 14 Jul 2011, at 15:57, Alan Gresley wrote:
>  | <semitones>
> 
>  | Specifies a relative change (decrement or increment)
>  | to the inherited value. The syntax of allowed values
>  | is a <number> followed immediately by "st" (semitones).
>  | A semitone is half of a tone (a half step) on the
>  | standard diatonic scale. As such, a semitone doesn't
>  | correspond to a fixed frequency: the ratio between
>  | two consecutive frequencies separated by exactly one
>  | semitone is the twelfth root of two
>  | (approximately 1.05946).
> 
> The above does not quite sound correct. Part of what the WD says above concerning the 'twelfth root of two' [1] is actually the ratio scaling of the 'chromatic scale' [2] with has all steps a semitone apart and an even ratio increase/decrease in hertz. The 'diatonic scale' does not have this even scaling and it only has seven steps 'T-T-S-T-T-T-S'.

The formulation can be improved indeed (lifted straight from the SSML specification, by the way).

The prose is meant to remind readers that the concept of "semitone" in CSS-Speech is the same as the concept of "semitone" in the diatonic scale. And of course, the definition of "semitone" is the same in both the diatonic and chromatic scales.

Because each and every "step" (interval) on the equal temperament chromatic scale is exactly a semitone, perhaps we should refer to this instead of the diatonic scale. At any rate, we can definitely improve the prose.

> I also don't understand what the WD means by the part which says 'a semitone doesn't correspond to a fixed frequency'?

Well, a semitone interval cannot be translated into an equivalent pitch difference without referring to a specific base/starting frequency. In other words, the Hertz value corresponding to a semitone step is defined relatively to an initial pitch, thus why a semitone does not correspond to a "fixed" frequency.

If you have better wording in mind, please propose! :)
Many thanks!

Regards, Dan
Received on Thursday, 14 July 2011 17:12:58 GMT

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