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//-*- C++ -*-
/*
* lingot, a musical instrument tuner.
*
* Copyright (C) 2004-2007 Ibán Cereijo Graña, Jairo Chapela Martínez.
*
* This file is part of lingot.
*
* lingot 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.
*
* lingot 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 should have received a copy of the GNU General Public License
* along with lingot; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "lingot-gauge.h"
LingotGauge* lingot_gauge_new(FLT initial_position)
{
//
// ----- ERROR GAUGE FILTER CONFIGURATION -----
//
// dynamic model of the gauge:
//
// 2
// d d
// --- s(t) = k (e(t) - s(t)) - q -- s(t)
// 2 dt
// dt
//
// acceleration of gauge position 's(t)' linealy depends on the difference
// respect to the input stimulus 'e(t)' (destination position). Inserting
// a friction coefficient 'q', acceleration proportionaly diminish with
// velocity (typical friction in mechanics). 'k' is the adaptation constant,
// and depends on the gauge mass.
//
// with the following derivatives approximation (valid for high sample rate):
//
// d
// -- s(t) ~= (s[n] - s[n - 1])*fs
// dt
//
// 2
// d 2
// --- s(t) ~= (s[n] - 2*s[n - 1] + s[n - 2])*fs
// 2
// dt
//
// we can obtain a difference equation, and implement it with an IIR digital
// filter.
//
FLT k = 60;
// adaptation constant.
FLT q = 6;
// friction coefficient.
FLT a[] =
{
k + GAUGE_RATE*(q + GAUGE_RATE),
-GAUGE_RATE*(q + 2.0*GAUGE_RATE),
GAUGE_RATE*GAUGE_RATE};
FLT b[] =
{ k};
LingotGauge* gauge = malloc(sizeof(LingotGauge));
gauge->filter = lingot_filter_new( 2, 0, a, b );
lingot_gauge_compute(gauge, initial_position);
return gauge;
}
void lingot_gauge_destroy(LingotGauge* gauge)
{
lingot_filter_destroy(gauge->filter);
free(gauge);
}
void lingot_gauge_compute(LingotGauge* gauge, FLT sample)
{
gauge->position = lingot_filter_filter_sample(gauge->filter, sample);
}
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