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 58 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.

[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()
 {
     m_convolverL1.reset();
     m_convolverR1.reset();
     m_convolverL2.reset();
     m_convolverR2.reset();
     m_delayLineL.reset();
     m_delayLineR.reset();
@@ skipping 216 matching lines @@
 
 void HRTFPanner::trace(Visitor* visitor)
 {
     visitor->trace(m_databaseLoader);
     Panner::trace(visitor);
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)