The getFloatFrequencyData()
method of the AnalyserNode
Interface copies the current frequency data into a Float32Array
array passed into it.
Each item in the array represents the decibel value for a specific frequency. The frequencies are spread linearly from 0 to 1/2 of the sample rate. For example, for 48000
sample rate, the last item of the array will represent the decibel value for 24000
Hz.
If you need higher performance and don't care about precision, you can use AnalyserNode.getByteFrequencyData()
instead, which works on a Uint8Array
.
Syntax
var audioCtx = new AudioContext(); var analyser = audioCtx.createAnalyser(); var dataArray = new Float32Array(analyser.frequencyBinCount); // Float32Array should be the same length as the frequencyBinCount void analyser.getFloatFrequencyData(dataArray); // fill the Float32Array with data returned from getFloatFrequencyData()
Parameters
array
- The
Float32Array
that the frequency domain data will be copied to. For any sample which is silent, the value is-Infinity
.
If the array has fewer elements than theAnalyserNode.frequencyBinCount
, excess elements are dropped. If it has more elements than needed, excess elements are ignored.
Return value
None.
Example
const audioCtx = new AudioContext(); const analyser = audioCtx.createAnalyser(); // Float32Array should be the same length as the frequencyBinCount const myDataArray = new Float32Array(analyser.frequencyBinCount); // fill the Float32Array with data returned from getFloatFrequencyData() analyser.getFloatFrequencyData(myDataArray);
Drawing a spectrum
The following example shows basic usage of an AudioContext
to connect a MediaElementAudioSourceNode
to an AnalyserNode
. While the audio is playing, we collect the frequency data repeatedly with requestAnimationFrame()
and draw a "winamp bargraph style" to a <canvas>
element.
For more complete applied examples/information, check out our Voice-change-O-matic-float-data demo (see the source code too).
<!doctype html> <body> <script> const audioCtx = new AudioContext(); //Create audio source //Here, we use an audio file, but this could also be e.g. microphone input const audioEle = new Audio(); audioEle.src = 'my-audio.mp3';//insert file name here audioEle.autoplay = true; audioEle.preload = 'auto'; const audioSourceNode = audioCtx.createMediaElementSource(audioEle); //Create analyser node const analyserNode = audioCtx.createAnalyser(); analyserNode.fftSize = 256; const bufferLength = analyserNode.frequencyBinCount; const dataArray = new Float32Array(bufferLength); //Set up audio node network audioSourceNode.connect(analyserNode); analyserNode.connect(audioCtx.destination); //Create 2D canvas const canvas = document.createElement('canvas'); canvas.style.position = 'absolute'; canvas.style.top = 0; canvas.style.left = 0; canvas.width = window.innerWidth; canvas.height = window.innerHeight; document.body.appendChild(canvas); const canvasCtx = canvas.getContext('2d'); canvasCtx.clearRect(0, 0, canvas.width, canvas.height); function draw() { //Schedule next redraw requestAnimationFrame(draw); //Get spectrum data analyserNode.getFloatFrequencyData(dataArray); //Draw black background canvasCtx.fillStyle = 'rgb(0, 0, 0)'; canvasCtx.fillRect(0, 0, canvas.width, canvas.height); //Draw spectrum const barWidth = (canvas.width / bufferLength) * 2.5; let posX = 0; for (let i = 0; i < bufferLength; i++) { const barHeight = (dataArray[i] + 140) * 2; canvasCtx.fillStyle = 'rgb(' + Math.floor(barHeight + 100) + ', 50, 50)'; canvasCtx.fillRect(posX, canvas.height - barHeight / 2, barWidth, barHeight / 2); posX += barWidth + 1; } }; draw(); </script> </body>
Specifications
Specification | Status | Comment |
---|---|---|
Web Audio API The definition of 'getFloatFrequencyData()' in that specification. |
Working Draft |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
getFloatFrequencyData | Chrome Full support 14 | Edge Full support 12 | Firefox Full support 25 | IE No support No | Opera Full support 15 | Safari Full support 6 | WebView Android Full support Yes | Chrome Android Full support 18 | Firefox Android Full support 26 | Opera Android Full support 14 | Safari iOS Full support 6 | Samsung Internet Android Full support 1.0 |
Legend
- Full support
- Full support
- No support
- No support