add API to query signal value of audio-latency measurement

libs/ardour/ardour/mtdm.h

@@ -34,6 +34,7 @@ public:
     int    inv (void) { return _inv; }
     double del (void) { return _del; }
     double err (void) { return _err; }
+    float get_peak () { const float rv = _peak; _peak = 0; return rv; }
 
 private:
     class Freq {
@@ -54,6 +55,7 @@ private:
     int     _cnt;
     int     _inv;
     Freq    _freq [13];
+    float   _peak;
 };
 
 #endif /* __libardour_mtdm_h__ */

libs/ardour/mtdm.cc

@@ -23,6 +23,7 @@
 MTDM::MTDM (int fsamp)
   : _cnt (0)
   , _inv (0)
+  , _peak (0)
 {
     int   i;
     Freq  *F;
@@ -56,11 +57,13 @@ int MTDM::process (size_t len, float *ip, float *op)
     int    i;
     float  vip, vop, a, c, s;
     Freq   *F;
+		float peak = 0;
 
     while (len--)
     {
         vop = 0.0f;
 	vip = *ip++;
+	if (fabsf(vip) > peak) { peak = vip; }
 	for (i = 0, F = _freq; i < 13; i++, F++)
 	{
 	    a = 2 * (float) M_PI * (F->p & 65535) / 65536.0;
@@ -86,6 +89,8 @@ int MTDM::process (size_t len, float *ip, float *op)
 	}
     }
 
+    if (peak > _peak) { _peak = vip; }
+
     return 0;
 }