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

Source/platform/audio/HRTFPanner.cpp

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 27 matching lines @@
 
 namespace blink {
 
 // The value of 2 milliseconds is larger than the largest delay which exists in any HRTFKernel from the default HRTFDatabase (0.0136 seconds).
 // We ASSERT the delay values used in process() with this value.
 const double MaxDelayTimeSeconds = 0.002;
 
 const int UninitializedAzimuth = -1;
 const unsigned RenderingQuantum = 128;
 
+// Support sample rate from 3 kHz to 192 kHz.

[Raymond Toy, 2014/09/04 17:27:20]

This comment seems unrelated to the following code. Update it to match the code.
You probably want to explain why 32 and 4096 are appropriate limits on the fft
size.

[KhNo, 2014/09/05 05:03:25]

I changed logic to find correct fft size. Do not need more this magic values.

+const size_t minfftSize = 32;
+const size_t maxfftSize = 4096;
+const float coefficientSampleRate = 2756.25f;

[Raymond Toy, 2014/09/04 17:27:20]

No trialing "f" required according to blink style.

You probably explained this to me, but where does the 2765.25 come from? You'll
probably need to add a comment to say where this magic number comes from.

[KhNo, 2014/09/05 05:03:25]

Done.

+
 HRTFPanner::HRTFPanner(float sampleRate, HRTFDatabaseLoader* databaseLoader)
     : Panner(PanningModelHRTF)
     , m_databaseLoader(databaseLoader)
     , m_sampleRate(sampleRate)
     , m_crossfadeSelection(CrossfadeSelection1)
     , m_azimuthIndex1(UninitializedAzimuth)
     , m_elevation1(0)
     , m_azimuthIndex2(UninitializedAzimuth)
     , m_elevation2(0)
     , m_crossfadeX(0)
@@ skipping 14 matching lines @@
 
 HRTFPanner::~HRTFPanner()
 {
 }
 
 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.
-    ASSERT(sampleRate >= 44100 && sampleRate <= 96000.0);
-    return (sampleRate < 88200.0) ? 512 : 1024;
+    ASSERT(sampleRate >= 3000.f && sampleRate <= 192000.f);

[Raymond Toy, 2014/09/04 17:27:20]

No ".f" allowed per blink style guide.

[KhNo, 2014/09/05 05:03:25]

Done.

+
+    if (sampleRate < 3000.f)
+        return minfftSize;
+    if (sampleRate > 192000.f)
+        return maxfftSize;
+
+    int scale = floor(sampleRate / coefficientSampleRate);
+    return scale * minfftSize;

[Raymond Toy, 2014/09/04 17:27:20]

Don't you need to make sure the returned FFT size is a power of two?

[KhNo, 2014/09/05 05:03:25]

Yes, it is required. I think I missed it during update patch set.
I changed the logic to find correct fft size from array that is guaranteed power
of two.
Thanks for detailed checking.

 }
 
 void HRTFPanner::reset()
 {
     m_convolverL1.reset();
     m_convolverR1.reset();
     m_convolverL2.reset();
     m_convolverR2.reset();
     m_delayLineL.reset();
     m_delayLineR.reset();
@@ skipping 210 matching lines @@
 double HRTFPanner::latencyTime() const
 {
     // The latency of a FFTConvolver is also fftSize() / 2, and is in addition to its tailTime of the
     // same value.
     return (fftSize() / 2) / static_cast<double>(sampleRate());
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)