Compute the tail time for an IIRFilter from its coefficients

third_party/WebKit/Source/platform/audio/IIRFilter.h

Index: third_party/WebKit/Source/platform/audio/IIRFilter.h
diff --git a/third_party/WebKit/Source/platform/audio/IIRFilter.h b/third_party/WebKit/Source/platform/audio/IIRFilter.h
index de2d3c6b8bee9cbfc10fe25db6dc118485fb0859..173d21e846792d877ad63ef6c1d7c240d9d53dbd 100644
--- a/third_party/WebKit/Source/platform/audio/IIRFilter.h
+++ b/third_party/WebKit/Source/platform/audio/IIRFilter.h
@@ -30,6 +30,12 @@ class PLATFORM_EXPORT IIRFilter final {
                             float* mag_response,
                             float* phase_response);
 
+  // Compute the tail time of the IIR filter
+  double TailTime(double sample_rate);

[hongchan, 2017/05/12 16:24:05]

What's the frequency of this computation?

On a related note, I am aware that IIRFilter does not share its infra with any
other DSP kernel or platform components. Should we actually consider doing that?

It seems like TailTime() and ResetState() methods can be shared with other
similar components.

We can fix them later, but I think we should at least consider.

[Raymond Toy, 2017/05/12 17:33:18]

I don't quite understand this question?  The TailTime is always requested every
render quantum. For the IIR filter, the value is computed once during
construction and this just returns that value.
I don't understand what is being shared.
I don't understand this either.  The TailTime() value depends on the node.

[hongchan, 2017/05/12 17:36:45]

You answered this above. We compute just once.
I just looked at the header file. Two methods are shared with other friend
classes. Ignore my comments.

+
+  // Reset the internal state of the IIR filter to the initial state.
+  void ResetState();
+
  private:
   // Filter memory
   //