FFTDrawer/app/src/main/java/com/feemers/android/fftdrawer/SignalProcessing/ThresholdCalculator.java

package com.feemers.android.fftdrawer.SignalProcessing;

class ThresholdCalculator {
    private double[] m_buffer;
    private int m_windowSize;
    private int m_bufferCounter;
    private int m_bufferInitCounter;
    private double m_constantThresholdPart;
    private double m_adaptiveThresholdPart;

    public ThresholdCalculator(int windowSize) {
        if (windowSize <= 0) {
            throw new AssertionError("windowSize should be postive");
        }
        m_windowSize = windowSize;
        reset();
    }

    public double getThreshold() {
        // This method is meant for the use inside of a detector implementation
        // Should be called every time a new sensor value is available
        // Returns the sum of the constant part of the threshold (determined by the user) and the
        // adaptive part of the threshold (determined by the noise level of the signal)
        return m_constantThresholdPart + m_adaptiveThresholdPart;
    }

    public void setConstantThresholdPart(double constantThresholdPart) {
        // This method should be called when the User changes the constant part of the threshold with the GUI
        this.m_constantThresholdPart = constantThresholdPart;
    }

    public void onNewSample(double sample) {
        // store sample
        m_buffer[m_bufferCounter] = sample;
        // increase counter
        m_bufferCounter++;
        // check if we are on the end of Array -> go to start
        if (m_bufferCounter >= m_windowSize) {
            m_bufferCounter = 0;
        }

        // when we start the application we will have an arry with emty values
        // hence we define how many values are already new
        // after N_sample == windowSize this will have no further effect
        if (m_bufferInitCounter < m_windowSize) {
            m_bufferInitCounter++;
        }

        // now calculate Mean
        double absMean = 0;
        for (int i = 0; i < m_bufferInitCounter; i++) {
            double sampleVal = m_buffer[i];
            absMean += Math.sqrt(sampleVal * sampleVal);
        }
        m_adaptiveThresholdPart = absMean / m_bufferInitCounter;
    }

    // for reset this class reset
    public void reset() {
        m_bufferCounter = 0;
        m_bufferInitCounter = 0;
        m_buffer = new double[m_windowSize];
        for (int i = 0; i < m_windowSize; i++) {
            m_buffer[i] = 0;
        }
    }
}