# v_lpcar2db

## PURPOSE

V_LPCAR2DB LPC: Convert AR coefs to power spectrum in dB DB=(AR)

## SYNOPSIS

function [db,f]=v_lpcar2db(ar,np)

## DESCRIPTION

    V_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:

- v_rfft V_RFFT Calculate the DFT of real data Y=(X,N,D)

This function is called by:

## SOURCE CODE

    0001 function [db,f]=v_lpcar2db(ar,np)
    0002 %V_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: v_lpcar2db.m 10865 2018-09-21 17:22:45Z dmb $
    0015 %
    0016 %   VOICEBOX is a MATLAB toolbox for speech processing.
    0017 %   Home page: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html
    0018 %
    0019 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    0020 %   This program is free software; you can redistribute it and/or modify
    0021 %   it under the terms of the GNU Lesser General Public License as published by
    0022 %   the Free Software Foundation; either version 3 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 Lesser General Public License for more details.
    0029 %
    0030 %   You can obtain a copy of the GNU Lesser General Public License from
    0031 %   https://www.gnu.org/licenses/ .
    0032 %
    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=v_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