SD = 1 L { ??? i = 1 L SD ( l ) } = 1 L { ??? i = 1 L 10 log 10 4 K ??? j = 1 K / 2 ( log 10 [ SP t ( l ) ( ?? j ) ] - log 10 [ SP t ( l ) ( ?? j ) ] ) 2 } Expression??????(4) where in Expression (4), L is the number data frames used for evaluation, l is a frame number, K is the number of FFT points, SPt (l)(??j) is an FFT power spectrum of a quantization target of the lth processing frame, SPq (l