AnalyserNode should downmix channels to mono.

third_party/WebKit/LayoutTests/webaudio/resources/realtimeanalyser-testing.js

 function createGraph(options) {
     var context = new OfflineAudioContext(1, renderFrames, sampleRate);
 
     // Use a default sawtooth wave for the test signal.  We want something is a
     // bit more harmonic content than a sine wave, but otherwise it doesn't
     // really matter.
     var src = context.createOscillator();
     src.type = "sawtooth";
 
     var analyser = context.createAnalyser();
@@ skipping 59 matching lines @@
     return 20 * Math.log10(x);
 }
 
 // Clip the FFT magnitude so that values below |limit| are set to |limit|.  The
 // FFT must be in dB.  The input array is clipped in place.
 function clipMagnitude(limit, x) {
     for (var k = 0; k < x.length; ++k)
         x[k] = Math.max(limit, x[k])
 }
 
-// Compare the float frequency data in dB, |freqData|, against the expected
-// value, |expectedFreq|. |options| is a dictionary with the property
-// |floatRelError| for setting the comparison threshold.
+// Compare the float frequency data in dB, |freqData|, against the expected value,
+// |expectedFreq|. |options| is a dictionary with the property |floatRelError| for setting the
+// comparison threshold and |precision| for setting the printed precision.  Setting |precision| to
+// |undefined| means printing all digits.  If |options.precision} doesn't exist, use a default
+// precision.
 function compareFloatFreq(message, freqData, expectedFreq, options) {
     // Any dB values below -100 is pretty much in the noise due to round-off in
     // the (single-precisiion) FFT, so just clip those values to -100.
     var lowerLimit = -100;
     clipMagnitude(lowerLimit, expectedFreq);
 
     var actual = freqData;
     clipMagnitude(lowerLimit, actual);
 
+    // Default precision for printing the FFT data.  Distinguish between options.precision existing
+    // or not.  If it does, use whatever value is there, including undefined.
+    var defaultPrecision = options.hasOwnProperty("precision") ? options.precision : 3;
+
     var success = Should(message, actual, {
             verbose: true,
-            precision: 3
+            precision: defaultPrecision
         })
         .beCloseToArray(expectedFreq, {
             relativeThreshold: options.floatRelError || 0,
         });
 
     return {
         success: success,
         expected: expectedFreq
     };
 }
@@ skipping 11 matching lines @@
 // Convert the float frequency data, |floatFreqData|, to byte values using the
 // dB limits |minDecibels| and |maxDecibels|.  The new byte array is returned.
 function convertFloatToByte(floatFreqData, minDecibels, maxDecibels) {
     var scale = 255 / (maxDecibels - minDecibels);
 
     return floatFreqData.map(function (x) {
         var value = Math.floor(scale * (x - minDecibels));
         return Math.min(255, Math.max(0, value));
     });
 }