function d=meansqtf(b,a)
%AVEPSPEC calculates the mean square transfer function for a filter D=(B,A)
%
% Inputs: B,A         Numerator and denominator filter coefficients.
%
% Output: D           The mean square transfer function of the filter B/A. This equals
%                     the average otuput power when the filter is fed with unit variance
%                     white noise.
%
%                     D may be obtained approximately by:
%                         N=1024; D=sum(filter(B,A,[1 zeros(1,N)]).^2)

% Since the power spectrum is the fourier transform of the autocorrelation, we can calculate
% the average value of pb/pa by taking the 0'th order term of the convolution of the autocorrelation
% functions associated with b and 1/a. Since b is an FIR filter, this convolution is
% a finite sum even though the autocorrelation function of 1/a is infinite in extent.

%      Copyright (C) Mike Brookes 1997
%      Version: $Id: meansqtf.m 713 2011-10-16 14:45:43Z dmb $
%
%   VOICEBOX is a MATLAB toolbox for speech processing.
%   Home page: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%   This program is free software; you can redistribute it and/or modify
%   it under the terms of the GNU General Public License as published by
%   the Free Software Foundation; either version 2 of the License, or
%   (at your option) any later version.
%
%   This program is distributed in the hope that it will be useful,
%   but WITHOUT ANY WARRANTY; without even the implied warranty of
%   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%   GNU General Public License for more details.
%
%   You can obtain a copy of the GNU General Public License from
%   http://www.gnu.org/copyleft/gpl.html or by writing to
%   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if length(a)==1
   d=(b(:)')*b(:);
else
   m=lpcar2ra(b(:)');
   m(1)=m(1)*0.5;
   d=2*lpcar2rr(a(:)',length(m)-1)*m';
end
