From the frequency response curve can you tell what type of

From the frequency response curve can you tell what type of filter it is: Frequency response curve is given below:

% Sampling frequency is 40 kHz

Fs = 40e3;

t = linspace(0,1,40e3);

% 1 kHz and 3 kHz sine waves

x = cos(2*pi*1e3*t)+0.5*sin(2*pi*3e3*t)+randn(size(t));

% Lowpass filter everything below 4 kHz

% Specify the filter

hlpf = fdesign.lowpass(\'Fp,Fst,Ap,Ast\',4e3,4.1e3,0.5,50,40e3);

% Design the filter

D = design(hlpf);

% apply the filter

y = filter(D,x);

subplot(211)

plot(t(1:1000),x(1:1000)); title(\'Original Waveform\');

subplot(212)

plot(t(1:1000),y(388:1000+387)); title(\'Filtered Waveform\');

figure;

subplot(211)

plot(psd(spectrum.periodogram,x,\'Fs\',Fs,\'NFFT\',length(x)));

title(\'Original Signal PSD\');

subplot(212);

plot(psd(spectrum.periodogram,y,\'Fs\',Fs,\'NFFT\',length(x)));

title(\'Filtered Signal PSD\');