WHITELF_SOUND(1)					      WHITELF_SOUND(1)



NAME
       whiteLF_sound - generate white noise directly to the sound card

SYNOPSIS
       whiteLF_sound [-d device] [-i infilename] [-v]

DESCRIPTION
       WhiteLF_sound  is for generating low passed white noise directly to the
       sound card.

       Sealed speaker enclosures exhibit a dual pole roll off below the enclo-
       sure  cutoff  frequency,  F3,  (this  is exactly true, in theory, for a
       critically damped design, almost true for a Bessel design or  maximally
       flat Butterworth design, and, approximately true for a Chebyshev design
       or acoustic suspension design.)

       To use a sealed enclosure for measuring room acoustics,	low  frequency
       contouring  is  necessary  for the speaker to supply a flat white noise
       response-meaning, providing the speaker with a dual pole bass boost.

       This program is a modification of the white_sound(1) program, and  pro-
       vides  two  poles  and two zeros in the generated white noise response.
       The pole frequency should be approximately a decade lower than  the  -6
       dB  frequency  of the speaker, (slightly below the -3 dB F3 cutoff fre-
       quency-a decade is not absolutely necessary, however,) and extends  the
       generated  response  to	down  -6 dB at approximately a decade lower in
       frequency, i.e., it extends the	flat  response	of  the  speaker  down
       approximately  a  decade,  albeit  with	very significant power ineffi-
       ciency, (but adequate for measuring most  room  acoustics  in  a  quiet
       environment.)

       The  flat  band high frequency gain and the pole frequency can be iter-
       ated, (via stdin,) in a near field measurement of the speaker for cali-
       bration	of flat response, then measurements taken at various locations
       in a room to derive the room's acoustical characteristics.

       A note about the algorithm. For each time sample, a white noise element
       is  generated and input to two recursive pole functions in series, (the
       pole frequency is specified by the double pole frequency, p  or	f.)  A
       second white noise element is generated, and the amplitude reduced, (by
       the factor of the flat band high frequency gain, g,)  and  summed  with
       the  output  of	the  two recursive poles to approximate the two zeros,
       thus generating a "flat band high frequency" white  noise.  This  tech-
       nique  is adequate for most purposes, and avoids the instability issues
       of generating zeros in the transfer function. Theoretically, this gives
       a  3  dB.  error, (since the two noise amplitudes add root-mean-square,
       instead of linearly,) which can be reduced, adequately, by altering the
       pole frequency when doing the near-field speaker alignment.

       The commands controlling the program are read from stdin, as EOL termi-
       nated records, and consist of a single character command followed by  a
       value, (if any):

	   Quit: e, q
	   Help: h
	   Print Values: p, v
	   Amplitude: a n, v n, 0 <= n <= 100, (1.0)
	   Double Pole Frequency: f n, p n, 1 <= n <= 1000, (5.3)
	   Flat Band High Frequency Gain: g n, 0 <= n <= 1, (0.01)

       Note:  the program waits for an input record on stdin before generating
       the white noise, (i.e., hit the Enter key when ready.)

OPTIONS
       -d device
	      sound device, (/dev/dsp).

       -i infilename
	      Input filename, (stdin).

       -v     Print the version and copyright banner of the program.

AUTHORS
       ----------------------------------------------------------------------

       A license is hereby granted to reproduce this software source code and
       to create executable versions from this source code for personal,
       non-commercial use.  The copyright notice included with the software
       must be maintained in all copies produced.

       THIS PROGRAM IS PROVIDED "AS IS". THE AUTHOR PROVIDES NO WARRANTIES
       WHATSOEVER, EXPRESSED OR IMPLIED, INCLUDING WARRANTIES OF
       MERCHANTABILITY, TITLE, OR FITNESS FOR ANY PARTICULAR PURPOSE.  THE
       AUTHOR DOES NOT WARRANT THAT USE OF THIS PROGRAM DOES NOT INFRINGE THE
       INTELLECTUAL PROPERTY RIGHTS OF ANY THIRD PARTY IN ANY COUNTRY.

       Copyright (c) 1994-2008, John Conover, All Rights Reserved.

       Comments and/or bug reports should be addressed to:

	   john@email.johncon.com (John Conover)

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			       February 18, 2008	      WHITELF_SOUND(1)