Extending supported sample rate from 3.0KHz to 192.0KHz for OfflineAudioContext.

Source/platform/audio/HRTFPanner.cpp

Index: Source/platform/audio/HRTFPanner.cpp
diff --git a/Source/platform/audio/HRTFPanner.cpp b/Source/platform/audio/HRTFPanner.cpp
index bab33c8173f42faf16cff3bb267d22271e99306c..a43f0d0b1f19d3b8bde8e16aeaf7f999384f969f 100644
--- a/Source/platform/audio/HRTFPanner.cpp
+++ b/Source/platform/audio/HRTFPanner.cpp
@@ -77,8 +77,13 @@ size_t HRTFPanner::fftSizeForSampleRate(float sampleRate)
     // The HRTF impulse responses (loaded as audio resources) are 512 sample-frames @44.1KHz.
     // Currently, we truncate the impulse responses to half this size, but an FFT-size of twice impulse response size is needed (for convolution).
     // So for sample rates around 44.1KHz an FFT size of 512 is good. We double the FFT-size only for sample rates at least double this.

[Raymond Toy, 2014/09/08 20:01:49]

Nit: Remove the sentence beginning with "We double...".

Probably replace that sentence with something like:

For different sample rates, the truncated response is resampled. The resampled
length is used to compute the FFT size by choosing a power of two that is
greater than or equal the resampled length. This power of two is doubled to get
the actual FFT size.

[KhNo, 2014/09/10 12:59:06]

Done.

-    ASSERT(sampleRate >= 44100 && sampleRate <= 96000.0);
-    return (sampleRate < 88200.0) ? 512 : 1024;
+    ASSERT(sampleRate >= 3000 && sampleRate <= 192000);
+
+    int impulseLength = 256;

[Raymond Toy, 2014/09/08 20:01:49]

Nit: I think I'd call this truncatedImpulseLength, to kind of match the comments
in line 78.

[KhNo, 2014/09/10 12:59:05]

Done.

+    double ratio = sampleRate / 44100;

[Raymond Toy, 2014/09/08 20:01:49]

Nit: Rename ratio to sampleRateRatio (to kind of match the names in
AudioBus.cpp)

[KhNo, 2014/09/10 12:59:05]

Done.

+    double resampledLength = impulseLength * ratio;
+
+    return 2 * (1 << static_cast<unsigned>(log2(resampledLength)));
 }
 
 void HRTFPanner::reset()