This creates an (lxl) matrix of random integers between 44 and 55:
y=randi([44,55],l)+x;
That is not what you want to do anyway.
To create uniformly-distributed noise between 44 and 55 Hz, try this:
[x,Fs,Nbits] = wavread('jennifer.wav');
Fn = Fs/2; % Nyquist Frequency (Hz)
Wp = [44 55]/Fn; % Passband Frequencies (Normalised)
Ws = [43 56]/Fn; % Stopband Frequencies (Normalised)
Rp = 10; % Passband Ripple (dB)
Rs = 50; % Stopband Ripple (dB)
[n,Ws] = cheb2ord(Wp,Ws,Rp,Rs); % Filter Order
[z,p,k] = cheby2(n,Rs,Ws); % Filter Design
[sosbp,gbp] = zp2sos(z,p,k); % Convert To Second-Order-Section For Stability
figure(3)
freqz(sosbp, 2^17, Fs)
L=length(x);
noise = rand(1, L); % Normally-Distributed Random Vector
noise_filt = filtfilt(sosbp, gbp, noise); % Filter Noise Signal
noisy_signal = x + noise_filt;
The filter code works, however I have not used this with your sound file. Note that the output of wavread and audioread scale (or normalise) the output to a maximum amplitude of ±1, so use the rand function, since its output is [0,1]. You may want to reduce the noise amplitude even further to avoid completely ‘swamping’ your audio signal in the noise.
