
A query to the selected Harmonicity object.
the standard deviation, expressed in dB.
The standard deviation between the times t_{1} and t_{2} is defined as
1/(t_{2}  t_{1}) ∫_{t1}^{t2} dt (x(t)  μ)^{2} 
where x(t) is the harmonicity (in dB) as a function of time, and μ its mean. For our discrete Harmonicity object, the standard deviation is approximated by
1/(n1) ∑_{i=m..m+n1} (x_{i}  μ)^{2} 
where n is the number of frame centres between t_{1} and t_{2}. Note the "minus 1".
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