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# lpcar2pf

## PURPOSE

LPCAR2PF Convert AR coefs to power spectrum PF=(AR,NP)

## SYNOPSIS

function [pf,f]=lpcar2pf(ar,np)

## DESCRIPTION

```LPCAR2PF Convert AR coefs to power spectrum PF=(AR,NP)

Inputs: ar(nf,n)     AR coefficients, one frame per row
np           Size of output spectrum is np+1 [n]

Outputs: pf(nf,np+1)  Power spectrum from DC to Nyquist
f(1,np+1)    Normalized frequencies (0 to 0.5)

For high speed make np equal to a power of 2```

## CROSS-REFERENCE INFORMATION

This function calls:
• rfft RFFT Calculate the DFT of real data Y=(X,N,D)
This function is called by:

## SOURCE CODE

```0001 function [pf,f]=lpcar2pf(ar,np)
0002 %LPCAR2PF Convert AR coefs to power spectrum PF=(AR,NP)
0003 %
0004 %  Inputs: ar(nf,n)     AR coefficients, one frame per row
0005 %          np           Size of output spectrum is np+1 [n]
0006 %
0007 % Outputs: pf(nf,np+1)  Power spectrum from DC to Nyquist
0008 %          f(1,np+1)    Normalized frequencies (0 to 0.5)
0009 %
0010 % For high speed make np equal to a power of 2
0011
0012 %      Copyright (C) Mike Brookes 1998-2014
0013 %      Version: \$Id: lpcar2pf.m 5026 2014-08-22 17:47:43Z dmb \$
0014 %
0015 %   VOICEBOX is a MATLAB toolbox for speech processing.
0017 %
0018 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0019 %   This program is free software; you can redistribute it and/or modify
0021 %   the Free Software Foundation; either version 2 of the License, or
0022 %   (at your option) any later version.
0023 %
0024 %   This program is distributed in the hope that it will be useful,
0025 %   but WITHOUT ANY WARRANTY; without even the implied warranty of
0026 %   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
0027 %   GNU General Public License for more details.
0028 %
0029 %   You can obtain a copy of the GNU General Public License from
0030 %   http://www.gnu.org/copyleft/gpl.html or by writing to
0031 %   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA.
0032 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0033
0034 [nf,p1]=size(ar);
0035 if nargin<2
0036     if nargout
0037         np=p1-1;
0038     else
0039         np=128;
0040     end
0041 end
0042 pf=abs(rfft(ar.',2*np).').^(-2);
0043 f=(0:np)/(2*np);
0044 if ~nargout
0045         plot(f,pf.');
0046         xlabel('Normalized frequency f/f_s');
0047         ylabel('LPC Power Spectrum');
0048 end
0049```

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