Fixed bug in peak interpolation algorithm in xtract_peak_spectrum()

5 files changed, 7 insertions, 1 deletions

diff --git a/src/delta.c b/src/delta.c
index 25d380b..b1effd0 100644
--- a/src/delta.c
+++ b/src/delta.c
@@ -26,6 +26,7 @@
 
 int xtract_flux(const float *data, const int N, const void *argv , float *result){
 
+    /* FIX: don't be lazy -- take the lnorm of the difference vector! */
     return xtract_lnorm(data, N, argv, result);
 
 }
diff --git a/src/scalar.c b/src/scalar.c
index 4a2b672..d2bc317 100644
--- a/src/scalar.c
+++ b/src/scalar.c
@@ -434,6 +434,8 @@ int xtract_spread(const float *data, const int N, const void *argv, float *resul
 	den += data[n];
     }
 
+    /* FIX: spectral spread is mathematically equivalent to spectral variance --
+     * here we are computing the spectral standard deviation */
     *result = sqrtf(num / den);
 
     return XTRACT_SUCCESS;
diff --git a/src/vector.c b/src/vector.c
index 449cd0d..b891111 100644
--- a/src/vector.c
+++ b/src/vector.c
@@ -436,7 +436,7 @@ int xtract_peak_spectrum(const float *data, const int N, const void *argv, float
     for(n = 1; n < N; n++){
         if(input[n] >= threshold){
             if(input[n] > input[n - 1] && input[n] > input[n + 1]){
-                result[N + n] = q * (n + (p = .5 * (y = input[n-1] - 
+                result[N + n] = q * (n + (p = .5 * ((y = input[n-1]) - 
 				(y3 = input[n+1])) / (input[n - 1] - 2 * 
 				    (y2 = input[n]) + input[n + 1])));
                 result[n] = y2 - .25 * (y - y3) * p;
diff --git a/xtract/xtract_delta.h b/xtract/xtract_delta.h
index 6e19708..152a891 100644
--- a/xtract/xtract_delta.h
+++ b/xtract/xtract_delta.h
@@ -39,6 +39,7 @@ extern "C" {
 
 /** \brief Extract flux 
  *
+ *  \note FIX: don't be lazy -- take the lnorm of the difference vector! 
  * An alias for xtract_lnorm()
  */
 int xtract_flux(const float *data, const int N, const void *argv , float *result);
diff --git a/xtract/xtract_scalar.h b/xtract/xtract_scalar.h
index 9bccb01..fdfb42a 100644
--- a/xtract/xtract_scalar.h
+++ b/xtract/xtract_scalar.h
@@ -394,6 +394,8 @@ int xtract_hps(const float *data, const int N, const void *argv, float *result);
  * \param *result: the pitch of N values from the array pointed to by *data
  *
  * This algorithm is based on the AMDF, with peak and centre clipping. It would benefit from further improvements to improve noise robustness and overall efficiency
+ *
+ * It is based on suggestion by Robert Bristow-Johnson in a discussion on the comp.dsp mailing list, subject "Reference implementation of pitch detection"
  * 
  */
 int xtract_f0(const float *data, const int N, const void *argv, float *result);