How can i use this audio equalizer code properly?

Hello guys,

I really have some troubles at the moment, because i had a homework to create an audio equalizer and i made all the things fine, and now, the last thing i have to do is to edit/modify the sound, to make it work properly.

I'm pretty newbie in matlab, but i found a usefull code(https://www.mathworks.com/matlabcentral/fileexchange/23982-digital-audio-equalizer) and i used some of it's parts to make the sliders in GUI and the code for editing the sound after i put in the playlist and press the play button. So, i will show you the code here:

    [x,Fs]=audioread(item_selected); %From here
    [a,b]=coef();
    l_bucata=2*Fs;
    Nb=round(length(x)/l_bucata);
    y=0;
    for ret=1:floor(Nb)
     bucata=x((ret-1)*l_bucata+1:ret*l_bucata);
      for k=1:5
       y=y+filter(10^(C(k)/20)*b{k},a{k},bucata); 
      end
    end %To here
    sunet=audioplayer(y,Fs); %I'm using this function and the playblocking thing to be able to use pause/resume/stop options
    playblocking(sunet);

Alright, so, FROM HERE, TO HERE, it's the paragraph where the sound will be edited, but i don't really understand what is wrong, because if i try to use sunet=audioplayer(x,Fs)/playblocking(sunet) it starts normally, but if i do the text that i wrote upthere, the sound starts to move very fast, doing weird things(like multi running in the same time), but the good thing is that the filters are working at all. I want to modify something to be able to listen the normal speed, and the whole song.

Thank you so much!