BiquadFilterNode.getFrequencyResponse()
The getFrequencyResponse()
method of the BiquadFilterNode
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
BiquadFilterNode.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 frequency response for each frequency value in thefrequencyArray
. For any frequency infrequencyArray
whose value is outside the range 0.0 tosampleRate
/2 (wheresampleRate
is the sample rate of theAudioContext
), the corresponding value in this array isNaN
. These are unitless values. phaseResponseOutput
-
A
Float32Array
to receive the computed phase response values in radians for each frequency value in the inputfrequencyArray
. For any frequency infrequencyArray
whose value is outside the range 0.0 tosampleRate
/2 (wheresampleRate
is the sample rate of theAudioContext
), the corresponding value in this array isNaN
.
Return value
Exceptions
InvalidAccessError
-
The three arrays provided are not all of the same length.
Example
In the following example we are using a biquad filter on a media stream (for the full
demo, see our stream-source-buffer
demo live, or read the
source.) As part of this demo, we get the frequency responses for this biquad
filter, for five sample frequencies. We first create the Float32Array
s 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>Biquad filter frequency response for: </p>
<ul class="freq-response-output">
</ul>
var freqResponseOutput = document.querySelector('.freq-response-output');
Finally, after creating our biquad 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 biquadFilter = audioCtx.createBiquadFilter();
biquadFilter.type = "lowshelf";
biquadFilter.frequency.value = 1000;
biquadFilter.gain.value = range.value;
...
function calcFrequencyResponse() {
biquadFilter.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
Specification |
---|
Web Audio API # dom-biquadfilternode-getfrequencyresponse |
Browser compatibility
BCD tables only load in the browser