I am getting an error that matlab does not recognize the function filter1 even though it is a matlab built-in function

%% Lab 3 Part 3

clc

clear

clf

% reads given audio file and puts it into y at frequency Fs

[y, Fs] = audioread('song_original.wav');

% starts playing original sound

%{

disp('sound start');

sound(y);

pause(10);

clear sound

disp('sound end');

%}

%% FFT

Z = fft(y);

t = (0:length(y)-1)/Fs;

t = transpose(t);

FD = 1/(mean(diff(t)));

L = numel(Z);

P2 = abs(Z/L);

P1 = P2(1:L/2+1);

P1(2:end-1) = 2*P1(2:end-1);

f = FD*(0:(L/2))/L;

%% Plot original sound file

plot(t,y,'k-','linewidth',1)

box off;

axis tight

xlabel 'time (seconds)'

%% Low Pass Filter

ylp = filterl('lp',y,'x',t,'fc',1100);

hold on

plot(t,ylp,'b')

Warning: Integer operands are required for colon operator when used

as index.

> In Lab3Part32 (line 25)

Undefined function or variable 'filterl'.

Error in Lab3Part32 (line 38)

ylp = filterl('lp',y,'x',t,'fc',1100);

>>

Answer 1

[Voss]

filter1 is not a built-in function, but it is available on the File Exchange:

https://www.mathworks.com/matlabcentral/fileexchange/53534-filter1

Download that, put it on your path, and try running your code again.

Answer 2

[Image Analyst]

I tried both filter1 ("one") and filterl ("L"). I'm not seeing either one in base MATLAB. It must be some function that you got (or thought you got) from somewhere or someone. Ask your professor for it. If he gave you a folder of utilities for your lab, then you must set a path to that folder.