The data you provided seems to already be in the frequency domain. If you could share the time domain audio data that would be more applicable to the link you shared. Otherwise, see below to simply smooth the data.
% Import the data
data = readtable("sample-data James Brown.txt");
% Convert to output type
data = table2array(data);
% Remove duplicate column in data
data = data(:,1);
% Plot original data
figure;
plot(data)
% Smooth data
dataSmooth = smoothdata(data,"movmean","SmoothingFactor",0.4);
% Plot smoothed data
hold on
plot(dataSmooth, "r")
hold off
