further constraints regarding bug 309, from off-list discussion with Steve

src/PitchName.cpp

@@ -31,7 +31,16 @@
 double FreqToMIDInoteNumber(double freq)
 {
    // Make the calculation relative to A440 (A4), note number 69. 
-   return double (69.0 + (12.0 * (log(freq / 440.0) / log(2.0))));
+   double dCalc = 69.0 + (12.0 * (log(freq / 440.0) / log(2.0)));
+   //vvv For freq values in the range (0.0, ~8.2], that calculation 
+   // produces negative dCalc, and as close in frequency as they are, 
+   // their modulo 12 results are different. 
+   // Also, not clear that any of those frequencies is a "pitch", 
+   // so pending further discussion, just enforce a floor.
+   // MIDI numbers are non-negative. 
+   if (dCalc < 0.0)
+      dCalc = 0.0;
+   return dCalc;
 }
 
 // PitchIndex returns the [0,11] index for a double pitchNum, 

src/effects/ChangePitch.cpp

@@ -462,6 +462,7 @@ bool ChangePitchDialog::TransferDataFromWindow()
 
 // calculations
 
+//vvvvv Probaly unnecessary with fix to FreqToMIDInoteNumber(), but leave it in until we decide how to handle very low freq values. 
 void ChangePitchDialog::Calc_FromPitchIndex()
 {
    m_FromPitchIndex = (int)(m_ToPitchIndex - m_SemitonesChange) % 12;
@@ -600,16 +601,17 @@ void ChangePitchDialog::OnText_FromFrequency(wxCommandEvent & WXUNUSED(event))
       this->Calc_ToFrequency();
       this->Calc_ToPitchIndex();
 
+      //vvvvv Probaly unnecessary with fix to FreqToMIDInoteNumber(), but leave it in until we decide how to handle very low freq values. 
       // This is Steve's incremental fix for cross-updating issues related to bug 309. 
       // It's weird that in prior code (3 lines above this), we set m_FromPitchIndex, 
       // then call 2 Calc methods for the other members, and then this call to 
       // recalculate m_FromPitchIndex. Something's wrong there, but I want to figure 
       // out the overall best scheme, and this is an incremental fix. 
-      this->Calc_FromPitchIndex(); 
+      //   this->Calc_FromPitchIndex(); 
 
       m_bLoopDetect = true;
-      this->Update_Choice_ToPitch();
       this->Update_Choice_FromPitch();
+      this->Update_Choice_ToPitch();
       this->Update_Text_ToFrequency();
       m_bLoopDetect = false;