design lowpass butterworth filter

I am just a beginner, I want to design an IIR low-pass filter butterworth. when I use function Butterord and butter, it always has frequency response from 0db.

Here is my code and result

fpass = 2500; fstop = 4000; As = 95; Rp=3; fs=44100; %Data
wp=(fpass*2)/fs; ws=(fstop*2)/fs;
[n,Wn] = buttord(wp,ws,Rp,As);   
[b,a,k]  = butter(n,Wn);
fprintf('\n Bac cua bo loc = %2.0f \n',n) 
sos = zp2sos(b,a,k);                
freqz(sos,1024,fs) 

Ripple of pass-band is 3db and I want to design from 40db instead of from 0db like this. How can i do it ? please help me