Moving average filter for sound in MATLAB y[n] = b0x[n] +b1x[n-1]


I have this MA filter in matlab as following

 load handel;
 x = y;

 b0 = 0.5;
 b1 = 0.5;

 N = length(x); % Length of input signal
 y = zeros(size(x)); % Allocate space for outut

 y(1) = b0*x(1); % First sample, assuming x(0) = 0
  for n=2:N % Remaining samples
    y(n) = b0*x(n) + b1*x(n-1);
  end;

 soundsc(y,Fs);


I was asked to listen to the signal and describe it , well I have run the load handel without filter in matlab than i have run the signal with this filter , it sounds like that with filter the signal sounds more demped and less noise compared without filter and when i changed the b1 to b1 =-0.5 it hears only the descant the base of sound is gone . Now I want to know the reason behind.


What is the effect of the filter on the input signal which pass through the system?
what is the effect of the filter on input signal which pass through the system if we change b0= 0.5 and b1 = -0.5?
1.) The moving average filter works as a low pass filter. Consequently, it will attenuate the high-frequency part of the signal and passes the low-frequency part of the signal. Therefore, the output signal should sound flat. 

2.) If we change b0= 0.5 and b1 = -0.5, the filter works basically as a differentiator, subtracting one sample from another sample. In this case, the filter works as a high pass filter, attenuating the low-frequency part of the signal. Therefore, when listening to the output signal, the high-frequency part of the input signal should appear amplified.