function bartlettHann( t, T, A ) {
	T -= 1;
	return A * ( A0 - (A1*abs( (t/T)-0.5) ) - (A2*cospi( (2.0/T)*t) ) );
}
Evaluates a Bartlett-Hann window function.

@private
@param {integer} t - value at which to evaluate the function
@param {integer} T - period
@param {number} A - amplitude
@returns {number} function value