Struct contents reference from a non-struct array object

L=10000;

fs=48000;

[y,fs] = audioread('pp.wav');

left_channel = y(:,1);

right_channel = y(:,2);

b = left_channel - right_channel;

x_noise=b.val(1,1:L)/200;

and i'm getting 'Struct contents reference from a non-struct array object' error in line "x_noise=b.val(1,1:L)/200;". Please tell me the solution.

[madhan ravi]

whos b %?

[pankaj gupta]

b is the signal which is difference between left and right signal of an audio signal.