why should we use apre=[1] and bpre=[1 -0.95]; in pre-emphasis filtering?

apre=[1]; [s1,fs]=wavread('D:\PROJECT\STUTTERED SPEECH\asr codes\Voice Recognition and Identification System\train\s1.wav'); subplot(3,1,1) plot(s1) title('speech signal'); %sound(s1,f); % design pre-emphasis filter bpre=[1 -0.95]; %fvtool(bpre,apre); ypre=filter(bpre,apre,s1); subplot(3,1,2) plot(ypre); title('First filter response'); %sound(ypre,f); s3 = zeros(size(s1)); for j1 = 1:size(s1,2) s3(:,j1) = conv(s1(:,j1),ypre(:,j1),'same'); wavwrite(s3,fs,16, 'new_s3_signa.wav'); end subplot(3,1,3); plot(s3); title('speech after filtering'); %sound(m,fs);