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/*
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* DCfilter.h |
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* |
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* Copyright 2012 Tim Barrass. |
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* |
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* This file is part of Mozzi. |
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* |
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* Mozzi is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. |
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* |
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*/ |
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#ifndef DCFILTER_H |
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#define DCFILTER_H |
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/*
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tb2010 adapted from: |
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robert bristow-johnson, DSP Trick: Fixed-Point DC Blocking Filter with Noise-Shaping |
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http://www.dspguru.com/book/export/html/126
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y[n] = x[n] - x[n-1] + a * y[n-1] |
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Where y[n] is the output at the current time n, and x[n] is the input at the current time n. |
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also, see DC Blocker Algorithms, http://www.ingelec.uns.edu.ar/pds2803/materiales/articulos/04472252.pdf
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*/ |
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/**
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A DC-blocking filter useful for highlighting changes in control signals. |
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The output of the filter settles to 0 if the incoming signal stays constant. If the input changes, the |
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filter output swings to track the change and eventually settles back to 0. |
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*/ |
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class DCfilter |
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{ |
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public: |
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/**
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Instantiate a DC-blocking filter. |
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@param pole sets the responsiveness of the filter, |
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how long it takes to settle to 0 if the input signal levels out at a constant value. |
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*/ |
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DCfilter(float pole):acc(0),prev_x(0),prev_y(0) |
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{ |
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A = (int)(32768.0*(1.0 - pole)); |
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} |
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/* almost original
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// timing: 20us
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int next(int x) |
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{ |
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setPin13High(); |
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acc -= prev_x; |
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prev_x = (long)x<<15; |
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acc += prev_x; |
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acc -= A*prev_y; |
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prev_y = acc>>15; // quantization happens here
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int filtered = (int)prev_y; |
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// acc has y[n] in upper 17 bits and -e[n] in lower 15 bits
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setPin13Low(); |
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return filtered; |
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} |
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*/ |
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/**
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Filter the incoming value and return the result. |
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@param x the value to filter |
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@return filtered signal |
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*/ |
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// timing :8us
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inline |
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int next(int x) |
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{ |
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acc += ((long)(x-prev_x)<<16)>>1; |
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prev_x = x; |
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acc -= (long)A*prev_y; // acc has y[n] in upper 17 bits and -e[n] in lower 15 bits
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prev_y = (acc>>16)<<1; // faster than >>15 but loses bit 0
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if (acc & 32784) prev_y += 1; // adds 1 if it was in the 0 bit position lost in the shifts above
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return prev_y; |
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} |
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private: |
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long acc; |
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int prev_x, prev_y,A; |
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}; |
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/**
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@example 05.Control_Filters/DCFilter/DCFilter.ino |
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This example demonstrates the DCFilter class. |
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*/ |
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#endif // #ifndef DCFILTER_H
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@ -1,44 +0,0 @@ |
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/*
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============================================================================== |
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This file is part of Tal-NoiseMaker by Patrick Kunz. |
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Copyright(c) 2005-2010 Patrick Kunz, TAL |
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Togu Audio Line, Inc. |
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http://kunz.corrupt.ch
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This file may be licensed under the terms of of the |
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GNU General Public License Version 2 (the ``GPL''). |
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Software distributed under the License is distributed |
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on an ``AS IS'' basis, WITHOUT WARRANTY OF ANY KIND, either |
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express or implied. See the GPL for the specific language |
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governing rights and limitations. |
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You should have received a copy of the GPL along with this |
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program. If not, go to http://www.gnu.org/licenses/gpl.html
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or write to the Free Software Foundation, Inc., |
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
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============================================================================== |
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*/ |
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#if !defined(__OnePoleLP_h) |
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#define __OnePoleLP_h |
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class OnePoleLP { |
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public: |
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float inputs, outputs, lastOutput; |
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OnePoleLP() { |
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lastOutput = inputs = outputs = 0.0f; |
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} |
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~OnePoleLP() {} |
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void tick(float *sample, float cutoff) { |
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float p = (cutoff * 0.98f) * (cutoff * 0.98f) * (cutoff * 0.98f) * (cutoff * 0.98f); |
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outputs = (1.0f - p) * (*sample) + p * outputs; |
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*sample = outputs; |
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} |
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}; |
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#endif |
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