Defining Frequency Bands with Minim

Question

I'm using a Minim BeatDetect object to analyze the incoming microphone signal. BeatDetect uses FFT.

In the BeatDetect class, there are four functions of interest: isHat(), isKick(), isSnare() and isRange(int, int, int). The first three are customized versions of isRange(). What I'm trying to do is recognize more than just hat, kick and snare drums.

In order to do this, I need to understand the math in the methods isHat(), isKick() and isSnare(). I'm hoping someone here can help me. Here is the code for the 4 functions.

/**
 * In frequency energy mode this returns true if a beat corresponding to the
 * frequency range of a kick drum has been detected. This has been tuned to
 * work well with dance / techno music and may not perform well with other
 * styles of music. In sound energy mode this always returns false.
 * 
 * @return boolean: true if a kick drum beat has been detected
 * 
 * @example Analysis/FrequencyEnergyBeatDetection
 * 
 * @related BeatDetect
 */
public boolean isKick()
{
    if (algorithm == SOUND_ENERGY)
    {
        return false;
    }
    int upper = 6 >= spect.avgSize() ? spect.avgSize() : 6;
    return isRange(1, upper, 2);
}

/**
 * In frequency energy mode this returns true if a beat corresponding to the
 * frequency range of a snare drum has been detected. This has been tuned to
 * work well with dance / techno music and may not perform well with other
 * styles of music. In sound energy mode this always returns false.
 * 
 * @return boolean: true if a snare drum beat has been detected
 * 
 * @example Analysis/FrequencyEnergyBeatDetection
 * 
 * @related BeatDetect
 */
public boolean isSnare()
{
    if (algorithm == SOUND_ENERGY)
    {
        return false;
    }
    int lower = 8 >= spect.avgSize() ? spect.avgSize() : 8;
    int upper = spect.avgSize() - 1;
    int thresh = (upper - lower) / 3 + 1;
    return isRange(lower, upper, thresh);
}

/**
 * In frequency energy mode this returns true if a beat corresponding to the
 * frequency range of a hi hat has been detected. This has been tuned to work
 * well with dance / techno music and may not perform well with other styles
 * of music. In sound energy mode this always returns false.
 * 
 * @return boolean: true if a hi hat beat has been detected
 * 
 * @example Analysis/FrequencyEnergyBeatDetection
 * 
 * @related BeatDetect
 */
public boolean isHat()
{
    if (algorithm == SOUND_ENERGY)
    {
        return false;
    }
    int lower = spect.avgSize() - 7 < 0 ? 0 : spect.avgSize() - 7;
    int upper = spect.avgSize() - 1;
    return isRange(lower, upper, 1);
}

/**
 * In frequency energy mode this returns true if at least
 * <code>threshold</code> bands of the bands included in the range
 * <code>[low, high]</code> have registered a beat. In sound energy mode
 * this always returns false.
 * 
 * @param low
 *           int: the index of the lower band
 * @param high
 *           int: the index of the higher band
 * @param threshold
 *           int: the smallest number of bands in the range
 *           <code>[low, high]</code> that need to have registered a beat
 *           for this to return true
 * @return boolean: true if at least <code>threshold</code> bands of the bands
 *         included in the range <code>[low, high]</code> have registered a
 *         beat
 *         
 * @related BeatDetect
 */
public boolean isRange(int low, int high, int threshold)
{
    if (algorithm == SOUND_ENERGY)
    {
        return false;
    }
    int num = 0;
    for (int i = low; i < high + 1; i++)
    {
        if (isOnset(i))
        {
            num++;
        }
    }
    return num >= threshold;
}

I want to be able to recognize beats accurately across a range of instruments by manipulating the methods above. Can anybody help teach me what I need to recognize this?

Currently, I understand that the functions return true if a beat is detected within a specified range of frequency bands. What I don't understand is why the values for the parameters [low, high, threshold] in the functions correlate to specific instruments. Thanks for any input.