Flash CS3 Documentation

Programming ActionScript 3.0 > Working with sound > Capturing sound input > Detecting microphone activity

Detecting microphone activity

To conserve bandwidth and processing resources, Flash Player tries to detect when no sound is being transmitted by a microphone. When the microphone's activity level stays below the silence level threshold for a period of time, Flash Player stops transmitting the audio input and dispatches a simple ActivityEvent instead.

Three properties of the Microphone class monitor and control the detection of activity:

• The read-only activityLevel property indicates the amount of sound the microphone is detecting, on a scale from 0 to 100.
• The silenceLevel property specifies the amount of sound needed to activate the microphone and dispatch an ActivityEvent.ACTIVITY event. The silenceLevel property also uses a scale from 0 to 100, and the default value is 10.
• The silenceTimeout property describes the number of milliseconds that the activity level must stay below the silence level, until an ActivityEvent.ACTIVITY event is dispatched to indicate that the microphone is now silent. The default silenceTimeout value is 2000.

Both the Microphone.silenceLevel property and the Microphone.silenceTimeout property are read only, but their values can be changed by using the Microphone.setSilenceLevel() method.

In some cases, the process of activating the microphone when new activity is detected can cause a short delay. Keeping the microphone active at all times can remove such activation delays. Your application can call the Microphone.setSilenceLevel() method with the silenceLevel parameter set to zero to tell Flash Player to keep the microphone active and keep gathering audio data, even when no sound is being detected. Conversely, setting the silenceLevel parameter to 100 prevents the microphone from being activated at all.

The following example displays information about the microphone and reports on activity events and status events dispatched by a Microphone object:

import flash,events.ActivityEvent;
import flash,events.StatusEvent;
import flash.media.Microphone;

var deviceArray:Array = Microphone.names;
trace("Available sound input devices:");
for (var i:int = 0; i < deviceArray.length; i++)
{
    trace("   " + deviceArray[i]);
}

var mic:Microphone = Microphone.getMicrophone();
mic.gain = 60;
mic.rate = 11;
mic.setUseEchoSuppression(true);
mic.setLoopBack(true);
mic.setSilenceLevel(5, 1000);
    
mic.addEventListener(ActivityEvent.ACTIVITY, this.onMicActivity);
mic.addEventListener(StatusEvent.STATUS, this.onMicStatus);
    
var micDetails:String = "Sound input device name: " + mic.name + '\n';
micDetails += "Gain: " + mic.gain + '\n';
micDetails += "Rate: " + mic.rate + " kHz" + '\n';
micDetails += "Muted: " + mic.muted + '\n';
micDetails += "Silence level: " + mic.silenceLevel + '\n';
micDetails += "Silence timeout: " + mic.silenceTimeout + '\n';
micDetails += "Echo suppression: " + mic.useEchoSuppression + '\n';
trace(micDetails);

function onMicActivity(event:ActivityEvent):void
{
    trace("activating=" + event.activating + ", activityLevel=" + 
        mic.activityLevel);
}

function onMicStatus(event:StatusEvent):void
{
    trace("status: level=" + event.level + ", code=" + event.code);
}

When you run the above example, speak or makes noises into your system microphone and watch the resulting trace statements appear in a console or debug window.

Flash CS3