weird spectrogram result

Hello, im trying to produce spectrograms but I am only getting quite weid results and I dont know how to make it look nice (full coloured frequency bands)


the code is:

function [] = fft_comparison( signal1, signal2, name, FS )

error(nargchk(2,4,nargin));

if (nargin < 4)
    FS = 48000;
end
if (nargin < 3)
    name = 'FFt comparison';
end

signal1_L = signal1(:,1);
signal1_R = signal1(:,2);
signal2_L = signal2(:,1);
signal2_R = signal2(:,2);


%% fft 

left1 = fft(signal1_L);
right1 = fft(signal1_R);
left2 = fft(signal2_L);
right2 = fft(signal2_R);

nfft1 = 2^nextpow2(length(signal1));
nfft2 = 2^nextpow2(length(signal2));

%% plot


% figure('name', name);


subplot(2,2,1)
spectrogram(signal1_L,hann(1024),512,nfft1,FS,'yax
is');
title('Original left signal');
subplot(2,2,3)
spectrogram(signal2_L,hann(1024),512,nfft1,FS,'yax
is');
title('Modified left signal');
subplot(2,2,2)
spectrogram(signal1_R,hann(1024),512,nfft1,FS,'yax
is');
title('Original right signal');
subplot(2,2,4)
spectrogram(signal2_R,hann(1024),512,nfft1,FS,'yax
is');
title('Modified right signal');


end

Attachment:Capture.PNG (81280 bytes | downloaded 4 times)