Minim core
ugens
analysis
Name BeatDetect
Description The BeatDetect class allows you to analyze an audio stream for beats (rhythmic onsets). Beat Detection Algorithms by Frederic Patin describes beats in the following way:
The human listening system determines the rhythm of music by detecting a pseudo periodical succession of beats. The signal which is intercepted by the ear contains a certain energy, this energy is converted into an electrical signal which the brain interprets. Obviously, The more energy the sound transports, the louder the sound will seem. But a sound will be heard as a beat only if his energy is largely superior to the sound's energy history, that is to say if the brain detects a brutal variation in sound energy. Therefore if the ear intercepts a monotonous sound with sometimes big energy peaks it will detect beats, however, if you play a continuous loud sound you will not perceive any beats. Thus, the beats are big variations of sound energy.
In fact, the two algorithms in this class are based on two algorithms described in that paper.

To use this class, inside of draw() you must first call detect(), passing the AudioBuffer you want to analyze. You may then use the isXXX functions to find out what beats have occurred in that frame. For example, you might use isKick() to cause a circle to pulse.

BeatDetect has two modes: sound energy tracking and frequency energy tracking. In sound energy mode, the level of the buffer, as returned by level(), is used as the instant energy in each frame. Beats, then, are spikes in this value, relative to the previous one second of sound. In frequency energy mode, the same process is used but instead of tracking the level of the buffer, an FFT is used to obtain a spectrum, which is then divided into average bands using logAverages(), and each of these bands is tracked individually. The result is that it is possible to track sounds that occur in different parts of the frequency spectrum independently (like the kick drum and snare drum).

In sound energy mode you use isOnset() to query the algorithm and in frequency energy mode you use isOnset(int i), isKick(), isSnare(), and isRange() to query particular frequnecy bands or ranges of frequency bands. It should be noted that isKick(), isSnare(), and isHat() merely call isRange() with values determined by testing the algorithm against music with a heavy beat and they may not be appropriate for all kinds of music. If you find they are performing poorly with your music, you should use isRange() directly to locate the bands that provide the most meaningful information for you.

Examples
/**
  * This sketch demonstrates how to use the BeatDetect object song SOUND_ENERGY mode.<br />
  * You must call <code>detect</code> every frame and then you can use <code>isOnset</code>
  * to track the beat of the music.
  * <p>
  * This sketch plays an entire song, so it may be a little slow to load.
  * <p>
  * For more information about Minim and additional features, 
  * visit http://code.compartmental.net/minim/
  */
  
import ddf.minim.*;
import ddf.minim.analysis.*;

Minim minim;
AudioPlayer song;
BeatDetect beat;

float eRadius;

void setup()
{
  size(200, 200, P3D);
  minim = new Minim(this);
  song = minim.loadFile("marcus_kellis_theme.mp3", 2048);
  song.play();
  // a beat detection object song SOUND_ENERGY mode with a sensitivity of 10 milliseconds
  beat = new BeatDetect();
  
  ellipseMode(RADIUS);
  eRadius = 20;
}

void draw()
{
  background(0);
  beat.detect(song.mix);
  float a = map(eRadius, 20, 80, 60, 255);
  fill(60, 255, 0, a);
  if ( beat.isOnset() ) eRadius = 80;
  ellipse(width/2, height/2, eRadius, eRadius);
  eRadius *= 0.95;
  if ( eRadius < 20 ) eRadius = 20;
}
Constructors
BeatDetect();
BeatDetect(timeSize, sampleRate);
Parameters
timeSize   int: the size of the buffer
sampleRate   float: the sample rate of the samples in the buffer
Fields
FREQ_ENERGY   Constant used to request frequency energy tracking mode.

SOUND_ENERGY   Constant used to request sound energy tracking mode.

Methods
detect ( )   Analyze the samples in buffer. This is a cumulative process, so you must call this function every frame.

detectMode ( )   Set the object to use the requested algorithm. If an invalid value is passed, the function will report and error and default to BeatDetect.SOUND_ENERGY

detectSize ( )   In frequency energy mode this returns the number of frequency bands currently being used. In sound energy mode this always returns 0.

getDetectCenterFrequency ( )   Returns the center frequency of the ith frequency band. In sound energy mode this always returns 0.

isHat ( )   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.

isKick ( )   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.

isOnset ( )   In sound energy mode this returns true when a beat has been detected. In frequency energy mode this always returns false.

isRange ( )   In frequency energy mode this returns true if at least threshold bands of the bands included in the range [low, high] have registered a beat. In sound energy mode this always returns false.

isSnare ( )   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.

setSensitivity ( )   Sets the sensitivity of the algorithm. After a beat has been detected, the algorithm will wait for millis milliseconds before allowing another beat to be reported. You can use this to dampen the algorithm if it is giving too many false-positives. The default value is 10, which is essentially no damping. If you try to set the sensitivity to a negative value, an error will be reported and it will be set to 10 instead.

Usage Web & Application
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