biz.source_code.dsp.signal

Class ActivityDetector

java.lang.Object

biz.source_code.dsp.signal.ActivityDetector

public class ActivityDetector
extends Object

An activity detector that can be used to subdivide an audio signal into zones with sound and zones with silence.

The following model is used to find active and silent zones: The input signal is divided into segments according to whether the signal envelope level is above or below the threshold level. These segments are classified into the following types:

• active: The envelope level is above the threshold and the zone is equal or longer than the minimum for activity.
• silence: The envelope level is below the threshold and the zone is equal or longer than the minimum for silence.
• undef: The zone is too small. The envelope level of the zone may be above or below the threshold (but not mixed).

"undef" segments are then eliminated using the following rules:

• Adjacent "undef" segments are combined.
• An "undef" segment that is adjacent to an "active" segment is converted to "active".
• An "undef" segment that lies between two "silence" segments is converted to "silence".
• The start and the end of the signal are regarded as "silence".

The resulting "active" segments are combined into the active zones.

Constructor Summary

Constructors

Constructor and Description
ActivityDetector(float thresholdLevel, int minActivityLen, int minSilenceLen) Creates an activity detector.

Method Summary

Modifier and Type	Method and Description
int[]	process(float[] signalEnvelope) Processes the signal envelope and returns the positions of the active zones.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ActivityDetector

public ActivityDetector(float thresholdLevel,
                        int minActivityLen,
                        int minSilenceLen)

Creates an activity detector.

Parameters:

thresholdLevel - The threshold signal envelope level to distinguish activity from silence.

minActivityLen - The minimum number of samples for an "active" segment.

minSilenceLen - The minimum number of samples for a "silence" segment.

Method Detail

process

public int[] process(float[] signalEnvelope)

Processes the signal envelope and returns the positions of the active zones.

Parameters:

signalEnvelope - The envelope of the input signal.

Returns:

An array with the start and end positions of the active zones. The size of the array is twice the number of active zones. The sequence is: active1Start, active1End, active2Start, active2End, ...