Evaluation of In-Car Communication Systems - Digital Signal Processing for In-Vehicle Systems and Safety - page 92

, the speech and silent passages within
this signal can be detected. Therefore, the squared magnitude of s

By using the predefined test signal s ð n Þ

ð n Þ is calculated

and smoothed over the time:

2 2 2

s ð n Þ ¼ a j s ð n Þj þð aÞj s ð n Þj :

j j 1 1 (5.1)

. By means of this smoothed
discrete signal, the set of the sampling points for the speech and pause passages can
be derived by

The smoothing factor is chosen as a 2 ½ 0 : 001 ; 0 : 01

n o

2

T speech ¼ n j s ð n Þ j > S 0 ; (5.2)

n o

2

T pause ¼ n j s ð n Þ j < N 0 ; (5.3)

where S 0 gives the threshold for the speech passage detection and N 0 for the pause
passages; in addition, S 0 N 0 must hold. It is assumed that the signal recorded by

the binaural microphones is defined as

y i ð n Þ¼ h i ð n Þ s ð n Þþ b ð n Þ¼ u i ð n Þþ b ð n Þ; (5.4)

where b the impulse response between the

artificial mouth and the corresponding i -th binaural microphone, and u i ð

ð n Þ indicates the additive noise, h i ð n Þ

is equal to
the convolution of the impulse response and the test signal. By combining these
definitions, the noise power P B;i and the noisy speech power P Y;i can be estimated by

n Þ

X
n 2 T pause j

1

2

P B;i ¼

T pause

y i ð n Þj (5.5)

#

and

0 1

X

1

@

2

A

P U;i ¼

T speech

j y i ð n Þj P B;i ; (5.6)

#

n 2 T speech

where defines the cardinality of a given set. Hence, the logarithmic SNR in

dependence of the ear is defined as

#

P U;i P B;i

P B;i

SNR i ¼ 10 log 10

P U ; i
P B;i

¼ 10 log 10 1 : (5.7)