Confused about the error

[y,Fs] = audioread('access_Denied.3gpp');

timeWindow = 20e-3; lengthWindow = round(timeWindow*Fs); % number of samples per window

% third argument specifies the number of overlapping samples yBuffer = buffer(x, lengthWindow, round(lengthWindow*0.2));

Error using buffer Input must be a vector.

Error in filter_1 (line 50) yBuffer = buffer(x, lengthWindow, round(lengthWindow*0.2));