Bug 105912 – Biquad filter: The phase response is incorrect

• Status: RESOLVED
• Resolution: INVALID
• Component: Web Audio

[kdj]

The phase change of frequency values is not happening as expected.
Verified on Webkit-r137862.

Please find the example below here:

----------------------------------------------------------------------------------------------------------
       var duration = 2.0;
       var sampleRate = 44100.0;
       function {
            context = window.AudioContext;
            numberOfFrames = duration * sampleRate;
            filter = context.createBiquadFilter();
            source = context.createBufferSource();
......
            fre = new Float32Array(numberOfFrames);
            mag = new Float32Array(numberOfFrames);
            pha = new Float32Array(numberOfFrames);
......
            buffer = context.createBuffer(1,numberOfFrames, sampleRate);
            data = buffer.getChannelData(0);
......
            // data filled with random values 
	    // for e.g. data[i] = Math.sin(440.0 * Math.PI * i / sampleRate);
......
            source.buffer = buffer;
            filter.type = 7;
            filter.frequency.value = 495.0;
            filter.getFrequencyResponse(fre, mag, pha);
.......
            source.connect(filter);
            filter.connect(context.destination);
.......
        }
        var result = (pha[numberOfFrames/2] != pha[(numberOfFrames/2) - 1]);
        assert_true(result, "Check if BiquadFilterNode.ALLPASS filter changes the phase relationship");
----------------------------------------------------------------------------------------------------------

Expected behaviour: 'pha[numberOfFrames/2]' is not equal to 'pha[(numberOfFrames/2) - 1]' and result == true
Current Result: The value of result is coming as False.
Observed behaviour: pha[numberOfFrames/2] = pha[(numberOfFrames/2) - 1] = 0;

[Raymond Toy]

In the example code given, there a mistake.  The values of the fre array are not set so they're all initialized to 0.  getFrequencyResponse returns the response for the frequency values in fre, so the mag and phase arrays are all filled with the same values corresponding to the response at frequency 0.

Please submit a more complete example if this problem still occurs.

[kdj]

Thanks for notifying the error; Test case has the issue, so marking it as resolved and INVALID.
(In reply to comment #1)
> In the example code given, there a mistake.  The values of the fre array are not set so they're all initialized to 0.  getFrequencyResponse returns the response for the frequency values in fre, so the mag and phase arrays are all filled with the same values corresponding to the response at frequency 0.
> 
> Please submit a more complete example if this problem still occurs.