Displaying sound data using the SoundMixer.computeSpectrum() method

The following example looks at making a simple spectrum analyzer app using the drawing API and the SoundMixer.computeSpectrum() method. This is basically a revised version of the example I did on my other blog last year, the poorly named “SoundMixer.computeSpectrum()” entry.

I’ve updated the code somewhat to make it a bit prettier. You can find more information on the SoundMixer class and the computeSpectrum() method in the Adobe Flash CS3 documentation “Accessing raw sound data” in the Programming ActionScript 3.0 book.

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        creationComplete="init()">

    <mx:Script>
        <![CDATA[
            import mx.core.SoundAsset;

            [Embed('assets/song1.mp3')]
            private const song1:Class;

            private var mySong:SoundAsset = SoundAsset(new song1());

            private var byteArray:ByteArray = new ByteArray();

            private var timer:Timer;

            private function init():void {
                timer = new Timer(50);
                timer.addEventListener(TimerEvent.TIMER, doTimer);
            }

            private function doTimer(evt:TimerEvent):void {
                SoundMixer.computeSpectrum(byteArray, true);

                spr.graphics.clear();
                drawChannel(LEFT_CHANNEL_COLOR);
                drawChannel(RIGHT_CHANNEL_COLOR);
            }

            private function drawChannel(color:uint):void {
                var f:Number;
                var i:int;

                spr.graphics.lineStyle(1, color);
                spr.graphics.beginFill(color, 0.6);
                spr.graphics.moveTo(0, GRAPH_HEIGHT);
                for (i = 0; i < 256; i++) {
                    f = byteArray.readFloat();
                    spr.graphics.lineTo(i * 2, GRAPH_HEIGHT - ((f * GRAPH_HEIGHT)) * 0.75);
                }
                spr.graphics.lineTo(512, GRAPH_HEIGHT);
                spr.graphics.endFill();
            }

            private function playSong():void {
                mySong.play();
            }
        ]]>
    </mx:Script>

    <mx:Number id="GRAPH_WIDTH">512</mx:Number>
    <mx:Number id="GRAPH_HEIGHT">256</mx:Number>

    <mx:Number id="LEFT_CHANNEL_COLOR">0xFF0000</mx:Number>
    <mx:Number id="RIGHT_CHANNEL_COLOR">0x0000FF</mx:Number>

    <mx:ApplicationControlBar width="{GRAPH_WIDTH}">
        <mx:Label text="Left:" color="{LEFT_CHANNEL_COLOR}" fontWeight="bold" />
        <mx:Label text="Right:" color="{RIGHT_CHANNEL_COLOR}" fontWeight="bold" />
        <mx:Spacer width="100%" />
        <mx:Button label="Play" click="playSong(); timer.start()" />
    </mx:ApplicationControlBar>

    <mx:VBox id="hbox" width="{GRAPH_WIDTH}" height="{GRAPH_HEIGHT}" backgroundColor="white">
        <mx:Box id="spr" width="100%" height="100%" />
    </mx:VBox>

</mx:Application>

Here’s the modified version which uses the Flex 2 Charting components.

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        creationComplete="init()">

    <mx:Script>
        <![CDATA[
            import mx.charts.chartClasses.NumericAxis;
            import mx.core.SoundAsset;

            [Embed('assets/song1.mp3')]
            private const song1:Class;

            private var mySong:SoundAsset;
            private var byteArray:ByteArray;
            private var timer:Timer;

            private function init():void {
                byteArray = new ByteArray();

                timer = new Timer(50); /* 50 milliseconds (20x/sec) */
                timer.addEventListener(TimerEvent.TIMER, doTimer);
                timer.start();

                mySong = SoundAsset(new song1());
                // mySong.play();
            }

            private function doTimer(evt:TimerEvent):void {
                var i:int;
                var f:Number;

                SoundMixer.computeSpectrum(byteArray, true);

                leftCh.removeAll();
                for (i = 0; i < 256; i++) {
                    f = byteArray.readFloat();
                    leftCh.addItem({data:f});
                }

                rightCh.removeAll();
                for (i = 0; i < 256; i++) {
                    f = byteArray.readFloat();
                    rightCh.addItem({data:f});
                }
            }
        ]]>
    </mx:Script>

    <mx:ArrayCollection id="leftCh" />
    <mx:ArrayCollection id="rightCh" />

    <mx:ApplicationControlBar dock="true">
        <mx:Button label="play audio" click="mySong.play();" />
    </mx:ApplicationControlBar>

    <mx:ColumnChart id="barChart" width="100%" height="100%">
        <mx:verticalAxis>
            <mx:LinearAxis minimum="0" maximum="1.4" />
        </mx:verticalAxis>

        <mx:series>
            <mx:ColumnSeries dataProvider="{leftCh}" yField="data" displayName="Left" />
            <mx:ColumnSeries dataProvider="{rightCh}" yField="data" displayName="Right" />
        </mx:series>
    </mx:ColumnChart >

</mx:Application>