Audio Filtering with fdesign

Hi, I want to filter audio : 20Hz-20kHz, I mean removing frequencies lower than 20Hz and higher than 20kHz, I apply bandpass filter (Fs is my sampling frequency and known before this line in programme), hlpf=fdesign.lowpass('Fp,Fst,Ap,Ast',20,20e4,2,60,Fs)

Is it wrong? I check it's output file with another audio software, and the filtered signal is in the picture, Thanks for help.