comparison loudness.js @ 407:a457b56ee928 Dev_main

Added loudness.js to handle loudness detection modules.

+/**
+ *  loundess.js
+ *  Loudness module for the Web Audio Evaluation Toolbox
+ *  Allows for automatic calculation of loudness of Web Audio API Buffer objects,
+ * 	return gain values to correct for a target loudness or match loudness between
+ *  multiple objects
+ */
+
+function getLoudness(buffer, result, timescale, offlineContext)
+{
+	// This function returns the EBU R 128 specification loudness model
+	// buffer -> Web Audio API Buffer object
+	// timescale -> M or Momentary (returns Array), S or Short (returns Array),
+	//   I or Integrated (default, returns number)
+	
+	// Create the required filters
+	if (buffer == undefined || result == undefined)
+	{
+		return 0;
+	}
+	if (timescale == undefined)
+	{
+		timescale = "I";
+	}
+	if (offlineContext == undefined)
+	{
+		offlineContext = new OfflineAudioContext(buffer.numberOfChannels, buffer.length, buffer.sampleRate);
+	}
+	var KFilter = offlineContext.createBiquadFilter();
+	KFilter.type = "highshelf";
+	KFilter.gain.value = 4;
+	KFilter.frequency.value = 1480;
+	
+	var HPFilter = offlineContext.createBiquadFilter();
+	HPFilter.type = "highpass";
+	HPFilter.Q.value = 0.707;
+	HPFilter.frequency.value = 60;
+	// copy Data into the process buffer
+	var processSource = offlineContext.createBufferSource();
+	processSource.buffer = buffer;
+	
+	processSource.connect(KFilter);
+	KFilter.connect(HPFilter);
+	HPFilter.connect(offlineContext.destination);
+	processSource.start();
+	offlineContext.startRendering().then(function(renderedBuffer) {
+		// Have the renderedBuffer information, now continue processing
+		console.log(renderedBuffer);
+		switch(timescale)
+		{
+		case "I":
+			var blockEnergy = calculateProcessedLoudness(renderedBuffer, 400, 0.75);
+			// Apply the absolute gate
+			var loudness = calculateLoudnessFromChannelBlocks(blockEnergy);
+			var absgatedEnergy = new Array(blockEnergy.length);
+			for (var c=0; c<blockEnergy.length; c++)
+			{
+				absgatedEnergy[c] = [];
+			}
+			for (var i=0; i<loudness.length; i++)
+			{
+				if (loudness[i] >= -70)
+				{
+					for (var c=0; c<blockEnergy.length; c++)
+					{
+						absgatedEnergy[c].push(blockEnergy[c][i]);
+					}
+				}
+			}
+			var overallAbsLoudness = calculateOverallLoudnessFromChannelBlocks(absgatedEnergy);
+			
+			//applying the relative gate 8 dB down from overallAbsLoudness
+			var relGateLevel = overallAbsLoudness - 8;
+			var relgateEnergy = new Array(blockEnergy.length);
+			for (var c=0; c<blockEnergy.length; c++)
+			{
+				relgateEnergy[c] = [];
+			}
+			for (var i=0; i<loudness.length; i++)
+			{
+				if (loudness[i] >= relGateLevel)
+				{
+					for (var c=0; c<blockEnergy.length; c++)
+					{
+						relgateEnergy[c].push(blockEnergy[c][i]);
+					}
+				}
+			}
+			var overallRelLoudness = calculateOverallLoudnessFromChannelBlocks(relgateEnergy);
+			result[0] =  overallRelLoudness;
+		}
+	}).catch(function(err) {
+		console.log(err);
+		result[0] = 1;
+	});
+}
+
+function calculateProcessedLoudness(buffer, winDur, overlap)
+{
+	// Buffer		Web Audio buffer node
+	// winDur		Window Duration in milliseconds
+	// overlap		Window overlap as normalised (0.5 = 50% overlap);
+	if (buffer == undefined)
+	{
+		return 0;
+	}
+	if (winDur == undefined)
+	{
+		winDur = 400;
+	}
+	if (overlap == undefined)
+	{
+		overlap = 0.5;
+	}
+	var winSize = buffer.sampleRate*winDur/1000;
+	var olapSize = overlap*winSize;
+	var numberOfFrames = Math.floor(buffer.length/olapSize - winSize/olapSize + 1);
+	var blockEnergy = new Array(buffer.numberOfChannels);
+	for (var channel = 0; channel < buffer.numberOfChannels; channel++)
+	{
+		blockEnergy[channel] = new Float32Array(numberOfFrames);
+		var data = buffer.getChannelData(channel);
+		for (var i=0; i<numberOfFrames; i++)
+		{
+			var sigma = 0;
+			for (var n=i*olapSize; n < i*olapSize+winSize; n++)
+			{
+				sigma += Math.pow(data[n],2);
+			}
+			blockEnergy[channel][i] = sigma/winSize;
+		}
+	}
+	return blockEnergy;
+}
+function calculateLoudnessFromChannelBlocks(blockEnergy)
+{
+	// Loudness
+	var loudness = new Float32Array(blockEnergy[0].length);
+	for (var i=0; i<blockEnergy[0].length; i++)
+	{
+		var sigma = 0;
+		for (var channel = 0; channel < blockEnergy.length; channel++)
+		{
+			var G = 1.0;
+			if (channel >= 4) {G = 1.41;}
+			sigma += blockEnergy[channel][i]*G;
+		}
+		loudness[i] = -0.691 + 10*Math.log10(sigma);
+	}
+	return loudness;
+}
+function calculateOverallLoudnessFromChannelBlocks(blockEnergy)
+{
+	// Loudness
+	var summation = 0;
+	for (var channel = 0; channel < blockEnergy.length; channel++)
+	{
+		var G = 1.0;
+		if (channel >= 4) {G = 1.41;}
+		var sigma = 0;
+		for (var i=0; i<blockEnergy[0].length; i++)
+		{
+			blockEnergy[channel][i] *= G;
+			sigma += blockEnergy[channel][i];
+		}
+		sigma /= blockEnergy.length;
+		summation+= sigma;
+	}
+	return -0.691 + 10*Math.log10(summation);;
+}