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# lpcar2db

## PURPOSE

LPCAR2DB LPC: Convert AR coefs to power spectrum in dB DB=(AR)

## SYNOPSIS

function [db,f]=lpcar2db(ar,np)

## DESCRIPTION

```LPCAR2DB LPC: Convert AR coefs to power spectrum in dB DB=(AR)

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

Outputs: db(nf,np+1)  Power spectrum in dB 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 [db,f]=lpcar2db(ar,np)
0002 %LPCAR2DB LPC: Convert AR coefs to power spectrum in dB DB=(AR)
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: db(nf,np+1)  Power spectrum in dB 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
0013 %      Copyright (C) Mike Brookes 1998
0014 %      Version: \$Id: lpcar2db.m 5026 2014-08-22 17:47:43Z dmb \$
0015 %
0016 %   VOICEBOX is a MATLAB toolbox for speech processing.
0018 %
0019 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0020 %   This program is free software; you can redistribute it and/or modify
0022 %   the Free Software Foundation; either version 2 of the License, or
0023 %   (at your option) any later version.
0024 %
0025 %   This program is distributed in the hope that it will be useful,
0026 %   but WITHOUT ANY WARRANTY; without even the implied warranty of
0027 %   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
0028 %   GNU General Public License for more details.
0029 %
0030 %   You can obtain a copy of the GNU General Public License from
0031 %   http://www.gnu.org/copyleft/gpl.html or by writing to
0032 %   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA.
0033 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0034
0035 [nf,p1]=size(ar);
0036 if nargin<2
0037     if nargout
0038         np=p1-1;
0039     else
0040         np=128;
0041     end
0042 end
0043 ff=rfft(ar.',2*np).';
0044 db=-10*log10(real(ff.*conj(ff)));
0045 f=(0:np)/(2*np);
0046 if ~nargout
0047         plot(f,db.');
0048         xlabel('Normalized frequency f/f_s');
0049         ylabel('LPC Power Spectrum (dB)');
0050 end
0051```

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