129333 2014-02-25 13:43:08 -0800 WaveShaperNode interpolation does not match specification 2014-02-28 01:35:38 -0800 1 1 1 Unclassified WebKit Web Audio 528+ (Nightly build) PC Windows XP NEW P2 Normal --- 1 webaudio.at.pendragon webkit-unassigned crogers webaudio.at.pendragon oldest_to_newest 984486 0 225181 webaudio.at.pendragon 2014-02-25 13:43:08 -0800 Created attachment 225181 HTML page that demonstates the bug (updated to work in Firefox too). The interpolation for the Web Audio WaveShaperNode does not work properly. I have created the follow JavaScript to demonstrate the 2 problems: var c=new webkitOfflineAudioContext(1, 23, 48000); //Create input values between -1.1 and + 1.1. var b=c.createBuffer(1, 23, 48000); var d=b.getChannelData(0); for (var i=0; i<23; i++){ d[i]=(i*.1)-1.1; } var src=c.createBufferSource(); src.buffer=b; src.start(0); //Simple wave-shaper. It should map -1 to 0, 0 to 1, and +1 to 0 - and interpolate all //points between. var ws=c.createWaveShaper(); var curve=new Float32Array(3); curve[0]=0; curve[1]=1; curve[2]=0; ws.curve=curve; src.connect(ws); ws.connect(c.destination); //Execute. c.oncomplete=function(ev){ var outputData=ev.renderedBuffer.getChannelData(0); var msgItems=[]; for (var i=0; i<23; i++){ msgItems.push("Input value " + d[i].toFixed(4) + " => output value " + outputData[i].toFixed(4)); } alert(msgItems.join("\n")); }; c.startRendering(); The specification says "Any sample value less than -1 will correspond to the first value in the curve array." * An input of -1.1 returns a value -0.1500, it should return 0.0000 The specification says "Each input sample within this range will index into the shaping curve with a signal level of zero corresponding to the center value of the curve array." * An input of 0 returns a value of 0.5000, it should return 1.0000 * An input of 0.4 returns a value of 0.0000, it should return 0.8000 The problem appears to be in WaveShaperDSPKernel.cpp - I think it should be changed to something like: double virtualIndex = 0.5 * (input + 1) * curveLength; double output; if (virtualIndex <= -1) { output = curve[0]; } else if (virtualIndex >= curve[curveLength-1]) { output = curve[curveLength-1]; } else { var index1 = (int)virtualIndex; var value1 = curve[index1]; var value2 = curve[index1+1]; var interpolationFactor = virtualIndex - index1; output = (1.0 - interpolationFactor) * value1 + interpolationFactor * value2; } The current test HTML page only tests input values that fall between -1 and +1 - and the error from the mid-point and end-point of the curve are disguised by the large number of elements in the curve array. 985503 1 225181 webaudio.at.pendragon 2014-02-28 01:35:38 -0800 Comment on attachment 225181 HTML page that demonstates the bug (updated to work in Firefox too). <html> <body> <pre> The interpolation for the Web Audio WaveShaperNode does not work properly. I have created the follow JavaScript to demonstrate the 2 problems: var audioContextClass=window.OfflineAudioContext||webkitOfflineAudioContext var c=new audioContextClass(1, 23, 48000); //Create input values between -1.1 and + 1.1. var b=c.createBuffer(1, 23, 48000); var d=b.getChannelData(0); for (var i=0; i<23; i++){ d[i]=(i*.1)-1.1; } var src=c.createBufferSource(); src.buffer=b; src.start(0); //Simple wave-shaper. It should map -1 to 0, 0 to 1, and +1 to 0 - and interpolate all //points between. var ws=c.createWaveShaper(); var curve=new Float32Array(3); curve[0]=0; curve[1]=1; curve[2]=0; ws.curve=curve; src.connect(ws); ws.connect(c.destination); //Execute. c.oncomplete=function(ev){ var inputData=b.getChannelData(0); var outputData=ev.renderedBuffer.getChannelData(0); var msgItems=[]; for (var i=0; i<23; i++){ msgItems.push("Input value " + inputData[i].toFixed(4) + " => output value " + outputData[i].toFixed(4)); } alert(msgItems.join("\n")); }; c.startRendering(); The specification says "Any sample value less than -1 will correspond to the first value in the curve array." * In Chrome, an input of -1.1 returns a value -0.1500, it should return 0.0000 The specification says "Each input sample within this range will index into the shaping curve with a signal level of zero corresponding to the center value of the curve array." * In Chrome and FireFox, an input of 0 returns a value of 0.5000, it should return 1.0000 * In Chrome and FireFox, an input of 0.4 returns a value of 0.0000, it should return 0.8000 The problem appears to be in WaveShaperDSPKernel.cpp in the webkit source code - I think it should be something like this: double virtualIndex = 0.5 * (input + 1) * curveLength; double output; if (virtualIndex <= -1) { output = curve[0]; } else if (virtualIndex >= curve[curveLength-1]) { output = curve[curveLength-1]; } else { int index1 = static_cast<int>(virtualIndex); double value1 = curve[index1]; double value2 = curve[index1+1]; double interpolationFactor = virtualIndex - index1; output = (1.0 - interpolationFactor) * value1 + interpolationFactor * value2; } The current webkit test HTML page only tests input values that fall between -1 and +1. The error from the mid-point and end-point of the curve are disguised by the large number of elements in the tested curve array. </pre> <script type="text/javascript"> var audioContextClass=(window.OfflineAudioContext||webkitOfflineAudioContext); var c=new audioContextClass(1, 23, 48000); //Create input values between -1.1 and + 1.1. var b=c.createBuffer(1, 23, 48000); var d=b.getChannelData(0); for (var i=0; i<23; i++){ d[i]=(i*.1)-1.1; } var src=c.createBufferSource(); src.buffer=b; src.start(0); //Simple wave-shaper. var ws=c.createWaveShaper(); var curve=new Float32Array(3); curve[0]=0; curve[1]=1; curve[2]=0; ws.curve=curve; src.connect(ws); ws.connect(c.destination); //Execute. c.oncomplete=function(ev){ var inputData=b.getChannelData(0); var outputData=ev.renderedBuffer.getChannelData(0); var msgItems=[]; for (var i=0; i<23; i++){ msgItems.push("Input value " + inputData[i].toFixed(4) + " => output value " + outputData[i].toFixed(4)); } alert(msgItems.join("\n")); }; c.startRendering(); </script> </body> </html> 225181 2014-02-25 13:43:08 -0800 2014-02-28 01:35:38 -0800 HTML page that demonstates the bug (updated to work in Firefox too). test.html text/html 3151 webaudio.at.pendragon PGh0bWw+DQo8Ym9keT4NCjxwcmU+DQpUaGUgaW50ZXJwb2xhdGlvbiBmb3IgdGhlIFdlYiBBdWRp byBXYXZlU2hhcGVyTm9kZSBkb2VzIG5vdCB3b3JrIHByb3Blcmx5Lg0KDQpJIGhhdmUgY3JlYXRl ZCB0aGUgZm9sbG93IEphdmFTY3JpcHQgdG8gZGVtb25zdHJhdGUgdGhlIDIgcHJvYmxlbXM6DQp2 YXIgYz1uZXcgd2Via2l0T2ZmbGluZUF1ZGlvQ29udGV4dCgxLCAyMywgNDgwMDApOw0KDQovL0Ny ZWF0ZSBpbnB1dCB2YWx1ZXMgYmV0d2VlbiAtMS4xIGFuZCArIDEuMS4NCnZhciBiPWMuY3JlYXRl QnVmZmVyKDEsIDIzLCA0ODAwMCk7DQp2YXIgZD1iLmdldENoYW5uZWxEYXRhKDApOw0KZm9yICh2 YXIgaT0wOyBpPDIzOyBpKyspeyBkW2ldPShpKi4xKS0xLjE7IH0NCnZhciBzcmM9Yy5jcmVhdGVC dWZmZXJTb3VyY2UoKTsNCnNyYy5idWZmZXI9YjsNCnNyYy5zdGFydCgwKTsNCg0KLy9TaW1wbGUg d2F2ZS1zaGFwZXIuIEl0IHNob3VsZCBtYXAgLTEgdG8gMCwgMCB0byAxLCBhbmQgKzEgdG8gMCAt IGFuZCBpbnRlcnBvbGF0ZSBhbGwNCi8vcG9pbnRzIGJldHdlZW4uDQp2YXIgd3M9Yy5jcmVhdGVX YXZlU2hhcGVyKCk7DQp2YXIgY3VydmU9bmV3IEZsb2F0MzJBcnJheSgzKTsNCmN1cnZlWzBdPTA7 DQpjdXJ2ZVsxXT0xOw0KY3VydmVbMl09MDsNCndzLmN1cnZlPWN1cnZlOw0Kc3JjLmNvbm5lY3Qo d3MpOw0Kd3MuY29ubmVjdChjLmRlc3RpbmF0aW9uKTsNCg0KLy9FeGVjdXRlLg0KYy5vbmNvbXBs ZXRlPWZ1bmN0aW9uKGV2KXsNCiAgdmFyIG91dHB1dERhdGE9ZXYucmVuZGVyZWRCdWZmZXIuZ2V0 Q2hhbm5lbERhdGEoMCk7DQogIHZhciBtc2dJdGVtcz1bXTsNCiAgZm9yICh2YXIgaT0wOyBpPDIz OyBpKyspew0KICAgIG1zZ0l0ZW1zLnB1c2goIklucHV0IHZhbHVlICIgKyBkW2ldLnRvRml4ZWQo NCkgKw0KICAgICAgIiA9PiBvdXRwdXQgdmFsdWUgIiArIG91dHB1dERhdGFbaV0udG9GaXhlZCg0 KSk7DQogIH0NCiAgYWxlcnQobXNnSXRlbXMuam9pbigiXG4iKSk7DQp9Ow0KYy5zdGFydFJlbmRl cmluZygpOw0KDQpUaGUgc3BlY2lmaWNhdGlvbiBzYXlzICJBbnkgc2FtcGxlIHZhbHVlIGxlc3Mg dGhhbiAtMSB3aWxsIGNvcnJlc3BvbmQgdG8gdGhlIGZpcnN0IHZhbHVlIGluIHRoZSBjdXJ2ZSBh cnJheS4iDQoqIEFuIGlucHV0IG9mIC0xLjEgcmV0dXJucyBhIHZhbHVlIC0wLjE1MDAsIGl0IHNo b3VsZCByZXR1cm4gMC4wMDAwDQoNClRoZSBzcGVjaWZpY2F0aW9uIHNheXMgIkVhY2ggaW5wdXQg c2FtcGxlIHdpdGhpbiB0aGlzIHJhbmdlIHdpbGwgaW5kZXggaW50byB0aGUgc2hhcGluZyBjdXJ2 ZQ0Kd2l0aCBhIHNpZ25hbCBsZXZlbCBvZiB6ZXJvIGNvcnJlc3BvbmRpbmcgdG8gdGhlIGNlbnRl ciB2YWx1ZSBvZiB0aGUgY3VydmUgYXJyYXkuIg0KKiBBbiBpbnB1dCBvZiAwIHJldHVybnMgYSB2 YWx1ZSBvZiAwLjUwMDAsIGl0IHNob3VsZCByZXR1cm4gMS4wMDAwDQoqIEFuIGlucHV0IG9mIDAu NCByZXR1cm5zIGEgdmFsdWUgb2YgMC4wMDAwLCBpdCBzaG91bGQgcmV0dXJuIDAuODAwMA0KDQpU aGUgcHJvYmxlbSBhcHBlYXJzIHRvIGJlIGluIFdhdmVTaGFwZXJEU1BLZXJuZWwuY3BwIC0gSSB0 aGluayBpdCBzaG91bGQgYmUgc29tZXRoaW5nIGxpa2UgdGhpczoNCg0KZG91YmxlIHZpcnR1YWxJ bmRleCA9IDAuNSAqIChpbnB1dCArIDEpICogY3VydmVMZW5ndGg7DQpkb3VibGUgb3V0cHV0Ow0K aWYgKHZpcnR1YWxJbmRleCA8PSAtMSkgew0KICBvdXRwdXQgPSBjdXJ2ZVswXTsNCn0gZWxzZSBp ZiAodmlydHVhbEluZGV4ID49IGN1cnZlW2N1cnZlTGVuZ3RoLTFdKSB7DQogIG91dHB1dCA9IGN1 cnZlW2N1cnZlTGVuZ3RoLTFdOw0KfSBlbHNlIHsNCiAgdmFyIGluZGV4MSA9IChpbnQpdmlydHVh bEluZGV4Ow0KICB2YXIgdmFsdWUxID0gY3VydmVbaW5kZXgxXTsNCiAgdmFyIHZhbHVlMiA9IGN1 cnZlW2luZGV4MSsxXTsNCiAgdmFyIGludGVycG9sYXRpb25GYWN0b3IgPSB2aXJ0dWFsSW5kZXgg LSBpbmRleDE7DQogIG91dHB1dCA9ICgxLjAgLSBpbnRlcnBvbGF0aW9uRmFjdG9yKSAqIHZhbHVl MSArIGludGVycG9sYXRpb25GYWN0b3IgKiB2YWx1ZTI7DQp9DQoNClRoZSBjdXJyZW50IHRlc3Qg SFRNTCBwYWdlIG9ubHkgdGVzdHMgaW5wdXQgdmFsdWVzIHRoYXQgZmFsbCBiZXR3ZWVuIC0xIGFu ZCArMSAtIGFuZCB0aGUNCmVycm9yIGZyb20gdGhlIG1pZC1wb2ludCBhbmQgZW5kLXBvaW50IG9m IHRoZSBjdXJ2ZSBhcmUgZGlzZ3Vpc2VkIGJ5IHRoZSBsYXJnZSBudW1iZXIgb2YNCmVsZW1lbnRz IGluIHRoZSBjdXJ2ZSBhcnJheS4NCjwvcHJlPg0KPHNjcmlwdCB0eXBlPSJ0ZXh0L2phdmFzY3Jp cHQiPg0KdmFyIGM9bmV3IHdlYmtpdE9mZmxpbmVBdWRpb0NvbnRleHQoMSwgMjMsIDQ4MDAwKTsN Cg0KLy9DcmVhdGUgaW5wdXQgdmFsdWVzIGJldHdlZW4gLTEuMSBhbmQgKyAxLjEuDQp2YXIgYj1j LmNyZWF0ZUJ1ZmZlcigxLCAyMywgNDgwMDApOw0KdmFyIGQ9Yi5nZXRDaGFubmVsRGF0YSgwKTsN CmZvciAodmFyIGk9MDsgaTwyMzsgaSsrKXsgZFtpXT0oaSouMSktMS4xOyB9DQp2YXIgc3JjPWMu Y3JlYXRlQnVmZmVyU291cmNlKCk7DQpzcmMuYnVmZmVyPWI7DQpzcmMuc3RhcnQoMCk7DQoNCi8v U2ltcGxlIHdhdmUtc2hhcGVyLg0KdmFyIHdzPWMuY3JlYXRlV2F2ZVNoYXBlcigpOw0KdmFyIGN1 cnZlPW5ldyBGbG9hdDMyQXJyYXkoMyk7DQpjdXJ2ZVswXT0wOw0KY3VydmVbMV09MTsNCmN1cnZl WzJdPTA7DQp3cy5jdXJ2ZT1jdXJ2ZTsNCnNyYy5jb25uZWN0KHdzKTsNCndzLmNvbm5lY3QoYy5k ZXN0aW5hdGlvbik7DQoNCi8vRXhlY3V0ZS4NCmMub25jb21wbGV0ZT1mdW5jdGlvbihldil7DQog IHZhciBvdXRwdXREYXRhPWV2LnJlbmRlcmVkQnVmZmVyLmdldENoYW5uZWxEYXRhKDApOw0KICB2 YXIgbXNnSXRlbXM9W107DQogIGZvciAodmFyIGk9MDsgaTwyMzsgaSsrKXsNCiAgICBtc2dJdGVt cy5wdXNoKCJJbnB1dCB2YWx1ZSAiICsgZFtpXS50b0ZpeGVkKDQpICsNCiAgICAgICIgPT4gb3V0 cHV0IHZhbHVlICIgKyBvdXRwdXREYXRhW2ldLnRvRml4ZWQoNCkpOw0KICB9DQogIGFsZXJ0KG1z Z0l0ZW1zLmpvaW4oIlxuIikpOw0KfTsNCmMuc3RhcnRSZW5kZXJpbmcoKTsNCjwvc2NyaXB0Pg0K PC9ib2R5Pg0KPC9odG1sPg==