www.pudn.com > voicebox2.zip > ERB2FRQ.M

function frq = erb2frq(erb) 
%ERB2FRQ  Convert ERB frequency scale to Hertz FRQ=(ERB) 
%	frq = erb2frq(erb) converts a vector of ERB-rate values 
%	to the corresponding frequencies in Hz. 
% 
%       Note that erb values must not exceed 42.79 
 
%	We have df/de = 6.23*f^2 + 93.39*f + 28.52 
%	where the above expression gives the Equivalent Rectangular 
%	Bandwidth (ERB)in Hz  of a human auditory filter with a centre 
%	frequency of f kHz. 
% 
%	By integrating the reciprocal of the above expression, we 
%	get: 
%		e = a ln((f/p-1)/(f/q-1))/c 
% 
%	where p and q are the roots of the equation: -0.312 and -14.7 
%  	and c = (6.23*(p-q))/1000 = 0.08950404 
% 
%	from this we can derive: 
% 
%	f = a/(b-exp(c*e)) - d 
% 
%	where a = 1000 q (1 - q/p) = 676170.4 
%	      b = q/p = 47.06538 
%	      d = -1000q = 14678.49 
%	and f is in Hz 
% 
%	References: 
% 
%	  [1] B.C.J.Moore & B.R.Glasberg "Suggested formula for 
%		calculating auditory-filter bandwidth and excitation 
%		patterns", J Acoust Soc America V74, pp 750-753, 1983 
% 
%	  [2] O. Ghitza, "Auditory Models & Human Performance in Tasks 
%		related to Speech Coding & Speech Recognition", 
%		IEEE Trans on Speech & Audio Processing, Vol 2, 
%		pp 115-132, Jan 1994 
%	 
 
 
 
%      Copyright (C) Mike Brookes 1998 
% 
%      Last modified Fri Apr  3 14:57:14 1998 
% 
%   VOICEBOX home page: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html 
% 
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%   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 
%   ftp://prep.ai.mit.edu/pub/gnu/COPYING-2.0 or by writing to 
%   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA. 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 
frq = 676170.4*(47.06538-exp(0.08950404*erb)).^(-1) - 14678.49;