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kmeterdsp.cc

/*
    Copyright (C) 2008 Fons Adriaensen <fons@kokkinizita.net>
    
    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 should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/


#include <math.h>
#include "kmeterdsp.h"


int    Kmeterdsp::_hold; 
float  Kmeterdsp::_fall; 
float  Kmeterdsp::_omega; 



Kmeterdsp::Kmeterdsp (void) :
    _z1 (0),
    _z2 (0),
    _rms (0),
    _dpk (0),
    _cnt (0),
    _flag (false)
{
}


Kmeterdsp::~Kmeterdsp (void)
{
}


void Kmeterdsp::process (float *p, int n)
{
    // Called by JACK's process callback.
    //
    // p : pointer to sample buffer
    // n : number of samples to process

    float  s, t, z1, z2;

    if (_flag) // Display thread has read the rms value.
    {
      _rms  = 0;
      _flag = 0;
    }

    // Get filter state.
    z1 = _z1;
    z2 = _z2;

    // Process n samples. Find digital peak value for this
    // period and perform filtering. The second filter is
    // evaluated only every 4th sample - this is just an
    // optimisation.
    t = 0;
    n /= 4;  // Loop is unrolled by 4.
    while (n--)
    {
      s = fabsf (*p++);             // Absolute value of next sample.
      if (t < s) t = s;             // Update digital peak.
      z1 += _omega * (s * s - z1);  // Update first filter.
      s = fabsf (*p++);             // Repeated four times.
      if (t < s) t = s;
      z1 += _omega * (s * s - z1);
      s = fabsf (*p++);
      if (t < s) t = s;
      z1 += _omega * (s * s - z1);
      s = fabsf (*p++);
      if (t < s) t = s;
      z1 += _omega * (s * s - z1);
        z2 += 4 * _omega * (z1 - z2); // Update second filter.
    }

    // Save filter state. The added constants avoid denormals.
    _z1 = z1 + 1e-20f;
    _z2 = z2 + 1e-20f;

    // Adjust RMS value and update maximum since last read().
    s = sqrtf (2 * z2);
    if (s > _rms) _rms = s;

    // Digital peak hold and fallback.
    if (t > _dpk)
    {
      // If higher than current value, update and set hold counter.
      _dpk = t;
      _cnt = _hold;
    }
    else if (_cnt) _cnt--; // else decrement counter if not zero,
    else
    {
        _dpk *= _fall;     // else let the peak value fall back,
      _dpk += 1e-10f;    // and avoid denormals.
    }
}


void Kmeterdsp::read (float *rms, float *dpk)
{
    // Called by display process approx. 30 times per second.
    //
    // Returns highest _rms value since last call, 
    // and current _dpk value.

    *rms = _rms;
    *dpk = _dpk;
    _flag = true; // Resets _rms in next process().
}


void Kmeterdsp::init (int fsamp, int fsize, float hold, float fall)
{
    // Called by initialisation code.
    //
    // fsamp = sample frequency
    // fsize = period size
    // hold  = peak hold time, seconds
    // fall  = peak fallback rate, dB/s

    float t;

    _omega = 9.72f / fsamp;                    // ballistic filter coefficient
    t = (float) fsize / fsamp;                 // period time in seconds
    _hold = (int)(hold / t + 0.5f);            // number of periods to hold peak
    _fall = powf (10.0f, -0.05f * fall * t);   // per period fallback multiplier
}

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