Long Term Average Spectrum of large batch of audio files
use "wavread()" to read the audio files 
use "pwelch()" to calculated the power spectrum of the songs
you do energy averagin over multiple songs.


Something like this (just a code sketch)

nx = 8192; % that's about 5 Hz @44.1 kHz
dd = dir('*.wav'); % all files in the current directory
nFiles = length(dd);
LTAS = zeros(nx/2+1,nFiles)
for i = 1:nFiles
  x = wavread(dd(i).name);
  LTAS(:,i) = pwelch(x,hanning(nx),nx/2);
end
LTASOverAllSongs = mean(LTAS,2);