diff --git a/aligner.py b/aligner.py
index 32e944a..bf1cbee 100644
--- a/aligner.py
+++ b/aligner.py
@@ -220,8 +220,9 @@ def interp_missing_1(ts):
     return np.array(tsl)
 
 
-def interp_missing(ts_a, ts_b):
+def interp_missing(ts_a_o, ts_b_o):
     """interpolate missing beats"""
+    ts_a, ts_b = np.array(ts_a_o), np.array(ts_b_o)  # deep copy
     assert len(ts_a) == len(ts_b)
     ib_th = 0.2  #: sec (inter-beat interval threshold for interpolation)
     mn_a, mn_b = np.mean(np.diff(ts_a)), np.mean(np.diff(ts_b))
@@ -229,14 +230,62 @@ def interp_missing(ts_a, ts_b):
     idxs_interp_b = np.where(np.abs(np.diff(ts_b) - mn_b) > ib_th)[0]
     # join the two sets, and apply interpolation to both timeseries
     # (ensures they will have the same length afterwards)
-    idxs_interp = np.array(list(sorted(list(set(idxs_interp_b).union(set(idxs_interp_b))))))
+    idxs_interp = list(sorted(list(set(idxs_interp_a).union(set(idxs_interp_b)))))
     tsl_a, tsl_b = list(ts_a), list(ts_b)
+    ma, mb = 0, 0
+    #print('idxs_interp_a', str(list(idxs_interp_a)))
+    #print('idxs_interp_b', str(list(idxs_interp_b)))
     for k, i in enumerate(idxs_interp):
-        tsl_a.insert(i+k+1, ts_a[i] + (ts_a[i+1] - ts_a[i]) / 2)
-        tsl_b.insert(i+k+1, ts_b[i] + (ts_b[i+1] - ts_b[i]) / 2)
-    if len(idxs_interp) > 0:
-        print('interp_missing: added %d beats' % len(idxs_interp))
-    return np.array(tsl_a), np.array(tsl_b)
+        ai = (ts_a[i+1] - ts_a[i])
+        bi = (ts_b[i+1] - ts_b[i])
+        # maybe we need to interpolate just on 'a' or 'b' side
+        # maybe we need to add more than 1 point
+        na, nb = int(np.round(ai / mn_a)), int(np.round(bi / mn_b))
+        #
+        # maybe we need to merge adjacent
+        """
+        if na == 0:
+            print('idx=%d: a interp (%.3f, %.3f), rm %d pts of %.3f interval' % (i, ts_a[i], ts_a[i+1], int(na-1), ai))
+            print('idx=%d: b interp (%.3f, %.3f), rm %d pts of %.3f interval' % (i, ts_b[i], ts_b[i+1], int(nb-1), bi))
+            print('  idx=%d: a1 %s' % (i, tsl_a[i+ma+1-3:i+ma+1+4]))
+            ts_a[i+1] = ts_a[i]
+            del tsl_a[i+ma]
+            print('  idx=%d: a2 %s' % (i, tsl_a[i+ma+1-3:i+ma+1+4]))
+            print('  idx=%d: b %s' % (i, tsl_b[i+mb+1-3:i+mb+1+4]))
+        if nb == 0:
+            print('idx=%d: a interp (%.3f, %.3f), rm %d pts of %.3f interval' % (i, ts_a[i], ts_a[i+1], int(na-1), ai))
+            print('idx=%d: b interp (%.3f, %.3f), rm %d pts of %.3f interval' % (i, ts_b[i], ts_b[i+1], int(nb-1), bi))
+            print('  idx=%d: b1 %s' % (i, tsl_b[i+mb+1-3:i+mb+1+4]))
+            ts_b[i+1] = ts_b[i]
+            del tsl_b[i+ma]
+            print('  idx=%d: b2 %s' % (i, tsl_b[i+mb+1-3:i+mb+1+4]))
+            print('  idx=%d: a %s' % (i, tsl_a[i+ma+1-3:i+ma+1+4]))
+        ai /= na if na != 0 else 1
+        bi /= nb if nb != 0 else 1
+        """
+        ai /= na if na != 0 else 1
+        bi /= nb if nb != 0 else 1
+        #
+        #print('idx=%d: a interp (%.3f, %.3f), add %d pts of %.3f interval' % (i, ts_a[i], ts_a[i+1], int(na-1), ai))
+        #print('idx=%d: b interp (%.3f, %.3f), add %d pts of %.3f interval' % (i, ts_b[i], ts_b[i+1], int(nb-1), bi))
+        #print('  idx=%d: a1 %s' % (i, tsl_a[i+ma+1-3:i+ma+1+4]))
+        for pa in range(int(na-1)):
+            tsl_a.insert(i+ma+pa+1, ts_a[i] + ai * (pa+1))
+        #print('  idx=%d: a2 %s' % (i, tsl_a[i+ma+1-3:i+ma+1+4]))
+        #print('  idx=%d: b1 %s' % (i, tsl_b[i+mb+1-3:i+mb+1+4]))
+        for pb in range(int(nb-1)):
+            tsl_b.insert(i+mb+pb+1, ts_b[i] + bi * (pb+1))
+        #print('  idx=%d: b2 %s' % (i, tsl_b[i+mb+1-3:i+mb+1+4]))
+        ma += int(na-1)
+        mb += int(nb-1)
+    #if len(idxs_interp) > 0:
+    #    print('interp_missing: added %d beats' % len(idxs_interp))
+    if ma > 0 or mb > 0:
+        print('interp_missing: added ma=%d mb=%d beats' % (ma, mb))
+    ll = len(ts_a) + min(ma, mb)
+    oa, ob = np.array(tsl_a)[:ll], np.array(tsl_b)[:ll]
+    print(len(ts_a), len(oa), len(ob))
+    return oa, ob
 
 
 def align(annot_a, annot_b):