Move utility functions for sample rate to AudioUtilities.

Source/platform/audio/AudioUtilities.cpp

 /*
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 #include "config.h"
 
 #if ENABLE(WEB_AUDIO)
 
 #include "platform/audio/AudioUtilities.h"
+
 #include "wtf/Assertions.h"
 #include "wtf/MathExtras.h"
 
 namespace blink {
 
 namespace AudioUtilities {
 
 float decibelsToLinear(float decibels)
 {
     return powf(10, 0.05f * decibels);
@@ skipping 12 matching lines @@
 
 double discreteTimeConstantForSampleRate(double timeConstant, double sampleRate)
 {
     return 1 - exp(-1 / (sampleRate * timeConstant));
 }
 
 size_t timeToSampleFrame(double time, double sampleRate)
 {
     return static_cast<size_t>(round(time * sampleRate));
 }
+
+bool isSampleRateRangeGood(float sampleRate)
+{
+    return sampleRate >= minAllowedSampleRate() && sampleRate <= maxAllowedSampleRate();
+}
+
+size_t fftSizeForSampleRate(float sampleRate)
+{
+    // Currently, we truncate the impulse responses to half this size,

[Raymond Toy, 2014/09/11 16:38:45]

Need more context here because "this size" has no meaning anymore.

[KhNo, 2014/09/12 15:01:05]

Done.

+    // 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.
+    // 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.
+
+    ASSERT(isSampleRateRangeGood(sampleRate));
+
+    int truncatedImpulseLength = 256;
+    double sampleRateRatio = sampleRate / 44100;
+    double resampledLength = truncatedImpulseLength * sampleRateRatio;
+
+    return 2 * (1 << static_cast<unsigned>(log2(resampledLength)));
+}
+
+float minAllowedSampleRate()
+{
+    // crbug.com/344375
+    return 3000;
+}
+
+float maxAllowedSampleRate()
+{
+    // Windows can support up to this rate.
+    return 192000;
+}
 } // AudioUtilites
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)