IIRFilterNode.getFrequencyResponse

The getFrequencyResponse() method of the IIRFilterNode interface takes the current filtering algorithm's settings and calculates the frequency response for frequencies specified in a specified array of frequencies.

The two output arrays, magResponseOutput and phaseResponseOutput, must be created before calling this method; they must be the same size as the array of input frequency values (frequencyArray).

Syntax

IIRFilterNode.getFrequencyResponse(frequencyArray, magResponseOutput, phaseResponseOutput);

Parameters

frequencyArray

A Float32Array containing an array of frequencies, specified in Hertz, which you want to filter.

magResponseOutput

A Float32Array to receive the computed magnitudes of the freqency response for each frequency value in the frequencyArray.

phaseResponseOutput

A Float32Array to receive the computed phase response values in radians for each frequency value in the input frequencyArray.

Return value

undefined

Exceptions

NotSupportedError

The three arrays provided are not all of the same length.

Example

In the following example we are using an IIR filter on a media stream (for a complete full demo, see our stream-source-buffer demo live, or read its source.) As part of this demo, we get the frequency responses for this IIR filter, for five sample frequencies. We first create the Float32Array objects we need, one containing the input frequencies, and two to receive the output magnitude and phase values:

var myFrequencyArray = new Float32Array(5);
myFrequencyArray[0] = 1000;
myFrequencyArray[1] = 2000;
myFrequencyArray[2] = 3000;
myFrequencyArray[3] = 4000;
myFrequencyArray[4] = 5000;

var magResponseOutput = new Float32Array(5);
var phaseResponseOutput = new Float32Array(5);

Next we create a <ul> element in our HTML to contain our results, and grab a reference to it in our JavaScript:

<p>IIR filter frequency response for: </p>
<ul class="freq-response-output">
</ul>

var freqResponseOutput = document.querySelector('.freq-response-output');

Finally, after creating our filter, we use getFrequencyResponse() to generate the response data and put it in our arrays, then loop through each data set and output them in a human-readable list at the bottom of the page:

var feedforwardCoefficients = [0.1, 0.2, 0.3, 0.4, 0.5];
var feedbackCoefficients = [0.5, 0.4, 0.3, 0.2, 0.1];

var iirFilter = audioCtx.createIIRFilter(feedforwardCoefficients, feedbackCoefficients);

  ...

function calcFrequencyResponse() {
  iirFilter.getFrequencyResponse(myFrequencyArray, magResponseOutput, phaseResponseOutput);

  for(i = 0; i <= myFrequencyArray.length-1;i++){
    var listItem = document.createElement('li');
    listItem.innerHTML = '<strong>' + myFrequencyArray[i] + 'Hz</strong>: Magnitude ' + magResponseOutput[i] + ', Phase ' + phaseResponseOutput[i] + ' radians.';
    freqResponseOutput.appendChild(listItem);
  }
}

calcFrequencyResponse();

Specifications

Browser compatibility

See also

• Using the Web Audio API
• IIRFilterNode
• AudioNode