comparison trunk/src/Modules/BMM/ModuleGammatone.h @ 288:34993448961f

-Updated the Slaney IIR gammatone to use a cascase of four second-order filters as per the implementtion in Slaney's auditory toolbox. This is more numerically stable at high sample rates and low centre frequencies.

  *  \brief Slaney's gammatone filterbank
  *
  *  \author Thomas Walters <[e-mail]>
  *  \date created 2009/11/13
  *  \version \$Id$
+ *
+ * This is the version of the IIR gammatone used in Slaney's Auditory toolbox.
+ * The original verison as described in Apple Tech. Report #35 has a problem
+ * with the high-order coefficients at low centre frequencies and high sample
+ * rates. Since it is important that AIM-C can deal with these cases (for
+ * example for the Gaussian features), I've reiplemeted Slaney's alternative
+ * version which uses a cascade of four second-order filters in place of the 
+ * eighth-order filter.
  */
 #ifndef _AIMC_MODULES_BMM_GAMMATONE_H_
 #define _AIMC_MODULES_BMM_GAMMATONE_H_
 
 #include <vector>

   virtual void Process(const SignalBank &input);
 
  private:
   virtual bool InitializeInternal(const SignalBank& input);
   virtual void ResetInternal();
-  vector<vector<float> > forward_;
-  vector<vector<float> > back_;
-  vector<vector<float> > state_;
-  vector<float> centre_frequencies_;
+
+  // Filter coefficients
+  vector<vector<double> > b1_;
+  vector<vector<double> > b2_;
+  vector<vector<double> > b3_;
+  vector<vector<double> > b4_;
+  vector<vector<double> > a_;
+
+  vector<vector<double> > state_1_;
+  vector<vector<double> > state_2_;
+  vector<vector<double> > state_3_;
+  vector<vector<double> > state_4_;
+
+  vector<double> centre_frequencies_;
   int num_channels_;
-  float max_frequency_;
-  float min_frequency_;
+  double max_frequency_;
+  double min_frequency_;
 };
 }  // namespace aimc
 #endif  // _AIMC_MODULES_BMM_GAMMATONE_H_