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    AudioListener

    This article is in need of a technical review.

    この記事はまだ日本語に翻訳されていません。MDN の翻訳はボランティアによって行われています。是非 MDN に登録し、私たちの力になって下さい。

    The AudioListener interface represents the position and orientation of the unique person listening to the audio scene, and is used in audio spatialisation. All PannerNodes spatialise in relation to the AudioListener stored in the AudioContext.listener attribute.

    It is important to note that there is only one listener per context and that it isn't an AudioNode.

    We see the position, up and front vectors of an AudioListener, with the up and front vectors at 90° from the other

    Properties

    Inherits properties from its parent, AudioNode.

    Methods

    Inherits methods from its parent, AudioNode.

    AudioListener.setOrientation()
    Defines the orientation of the listener.

    Deprecated features

    In a previous version of the specification, the three members listed below could be used to control the doppler effect applied to AudioBufferSourceNodes connected downstream — these would be pitched up and down according to the relative speed of the PannerNode and the AudioListener. These features had a number of problems:

    • Only AudioBufferSourceNodes were pitched up or down, not other source nodes.
    • The behavior to adopt when an AudioBufferSourceNode was connected to multiple PannerNodes was unclear.
    • Because the velocity of the panner and the listener were not AudioParams, the pitch modification could not be smoothly applied, resulting in audio glitches.
    AudioListener.dopplerFactor
    Is a double value representing the amount of pitch shift to use when rendering a doppler effect.
    AudioListener.speedOfSound
    Is a double value representing the speed of sound, in meters per second.
    AudioListener.setPosition()
    Defines the position of the listener.

    Example

    In the following example, you can see an example of how the createPanner() method, AudioListener  and PannerNode would be used to control audio spatialisation. Generally you will define the position in 3D space that your audio listener and panner (source) occupy initially, and then update the position of one or both of these as the application is used. You might be moving a character around inside a game world for example, and wanting delivery of audio to change realistically as your character moves closer to or further away from a music player such as a stereo. In the example you can see this being controlled by the functions moveRight(), moveLeft(), etc., which set new values for the panner position via the PositionPanner() function.

    To see a complete implementation, check out our panner-node example (view the source code) — this demo transports you to the 2.5D "Room of metal", where you can play a track on a boom box and then walk around the boom box to see how the sound changes!

    // define Web Audio API objects
    
    var AudioContext = window.AudioContext || window.webkitAudioContext;
    var audioCtx = new AudioContext();
    
    var panner = audioCtx.createPanner();
    panner.panningModel = 'HRTF';
    panner.distanceModel = 'inverse';
    panner.refDistance = 1;
    panner.maxDistance = 10000;
    panner.rolloffFactor = 1;
    panner.coneInnerAngle = 360;
    panner.coneOuterAngle = 0;
    panner.coneOuterGain = 0;
    panner.setOrientation(1,0,0);
    
    var listener = audioCtx.listener;
    listener.setOrientation(0,0,-1,0,1,0);
    
    var source;
    
    var boomBox = document.querySelector('.boom-box');
    
    // set up listener and panner position information
    var WIDTH = window.innerWidth;
    var HEIGHT = window.innerHeight;
    
    var xPos = WIDTH/2;
    var yPos = HEIGHT/2;
    var zPos = 295;
    
    leftBound = (-xPos) + 50;
    rightBound = xPos - 50;
    
    xIterator = WIDTH/150;
    
    // listener will always be in the same place for this demo
    listener.setPosition(xPos,yPos,300);
    listenerData.innerHTML = 'Listener data: X ' + xPos + ' Y ' + yPos + ' Z ' + 300;
    
    // panner will move as the boombox graphic moves around on the screen
    function positionPanner() {
      panner.setPosition(xPos,yPos,zPos);
      pannerData.innerHTML = 'Panner data: X ' + xPos + ' Y ' + yPos + ' Z ' + zPos;
    }
    
    // controls to move left and right past the boom box
    // and zoom in and out
    // only right movement code shown in this listing to save space
    // look at the source code for full listing
    
    var leftButton = document.querySelector('.left');
    var rightButton = document.querySelector('.right');
    var zoomInButton = document.querySelector('.zoom-in');
    var zoomOutButton = document.querySelector('.zoom-out');
    
    var boomX = 0;
    var boomY = 0;
    var boomZoom = 0.25;
    
    var zoomInLoop;
    var zoomOutLoop
    
    function moveRight() {
      boomX += -xIterator;
      xPos += -0.066;
    
      if(boomX <= leftBound) {
        boomX = leftBound;
        xPos = (WIDTH/2) - 5;
      }
    
      boomBox.style.transform = "translate(" + boomX + "px , " + boomY + "px) scale(" + boomZoom + ")";
      positionPanner();
      rightLoop = requestAnimationFrame(moveRight);
      return rightLoop;
    }
    
    rightButton.onmousedown = moveRight;
    rightButton.onmouseup = function () {
      window.cancelAnimationFrame(rightLoop);
    }

    Note: In terms of working out what position values to apply to the listener and panner, to make the sound appropriate to what the visuals are doing on screen, there is quite a bit of fiddly maths involved, but you will soon get used to it with a bit of experimentation.

    Specifications

    Specification Status Comment
    Web Audio API
    The definition of 'AudioListener' in that specification.
    Working Draft  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
    Basic support 10.0webkit 25.0 (25.0)  Not supported 15.0webkit
    22 (unprefixed)
    6.0webkit
    Feature Android Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
    Basic support ? 26.0 1.2 ? ? ? 33.0

    See also

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    最終更新者: chrisdavidmills,