diff --git a/beat.py b/beat.py
index 42fd664..ca2fbc1 100644
--- a/beat.py
+++ b/beat.py
@@ -1,4 +1,5 @@
 import numpy as np
+import matplotlib.pyplot as plt  # for debug only
 
 class SsfZxing:
     """
@@ -7,18 +8,16 @@ class SsfZxing:
     """
     t_holdoff = 0.1     #: hold-off period in sec (ignore zxings after initial rise)
     # these two depend on each other.
-    t_range = 0.024     #: rise amplitude range in sec: +/- around transition, we check the rise amplitude. about 2*sw_sec but nb. 0.008 sec steps in fs/D rate
+    t_range = 0.032     #: rise amplitude range in sec: +/- around transition, we check the rise amplitude. about 2*sw_sec but nb. 0.008 sec steps in fs/D rate
     sw_sec =  0.04      #: upslope width in sec (for SSF function)
-    ssf_rel_thres = 3   #: magic number from Zong 2003, to scale mean SSF amplitude
+    ssf_rel_thres = 3   #: magic number from Zong 2003, threshold from mean SSF amplitude
     ssf_rel_rise = 0.8  #: minimum rise of SSF edge (from foot to peak) relative to 'ssf_th'
 
     def __init__(self): pass
 
-    def _ssf_det_zxings(self, fs, ssf):
+    def _ssf_det_zxings(self, fs, ssf, ssf_th):
         """detect threshold crossings in 'ssf' signal."""
         i_holdoff = int(self.t_holdoff * fs)
-        # TODO: check if we need lowpass instead of mean for 'ssf_th'
-        ssf_th = self.ssf_rel_thres * np.mean(ssf)
         # threshold crossing
         ssf_pk = np.pad((ssf > ssf_th).astype(int), (0,1))
         ssf_pks = np.pad(ssf_pk[:-1], (1,0))
@@ -31,7 +30,7 @@ class SsfZxing:
         i_range = int(self.t_range * fs)
         for i in np.arange(i_range, ssf_z.shape[0]-i_range-1):
             if ssf_z[i]:
-                rise = ssf[i+i_range] - ssf[i-i_range]
+                rise = np.max(ssf[i:i+i_range]) - np.min(ssf[i-i_range:i])
                 if rise < ssf_th * self.ssf_rel_rise:
                     ssf_z[i] = 0
         ssf_z[-i_range:] = 0  # force-zero the bounds where we cannot check the amplitude rise
@@ -43,13 +42,15 @@ class SsfZxing:
     def _ssf_function(self, fs, y):
         """sum-slope function."""
         sw = int(self.sw_sec*fs)
-
         duk = np.clip(np.diff(np.pad(y, (1,0))), a_min=0, a_max=np.inf)  # left-looking window
         #ssf = np.convolve(duk, slope_filter, mode='same')  # centered window (acausal!)
         duks = np.pad(np.cumsum(duk), (0, sw))
         duks_r = np.roll(duks, sw)
         ssf = (duks - duks_r)[:-sw]
-        return ssf
+        # compute threshold
+        # TODO: check if we need lowpass instead of mean for 'ssf_th'
+        ssf_th = self.ssf_rel_thres * np.mean(ssf)
+        return ssf, ssf_th
 
 
 def get_mae_dist(ibis):
@@ -128,6 +129,11 @@ def get_mae_err(fs, freq, phase, act_ibis, debug=False):
     # (in direction 2, an optimal solution is "fully sparse", "freq = 1/L", because those are the only 'est_beats' which are aligned)
     mae += get_mae_err_1(fs, freq, phase, act_ibis, debug)
     mae += get_mae_err_2(fs, freq, phase, act_ibis, debug)
+    # TODO: may need to weight these two differently
+    # TODO: see "2027-04-27 TestApi_0b" vs "2027-04-27 TestApi" plots [24]
+    # TODO: (check: is match always slightly to the left of the trough / smooth minimum?)
+    # TODO (if so, we may need to weight dir1 and dir2 differently -- or maybe norm by pts density??)
+    # (or even penalize differently instead of adding dir1 and dir2)
     return mae
 
 class RegularBeatFinder:
diff --git a/segmenter.py b/segmenter.py
index cda868e..965d469 100644
--- a/segmenter.py
+++ b/segmenter.py
@@ -9,6 +9,8 @@ def median_filter(a, w):
         o[i] = np.median(sl)
     return o
 
+# nice-to: split longer segments (above 30 sec), merge very-short segments
+
 class Segmenter:
     seg_win_size_sec = 4.0  #: window size for stat. measures for segmentation, in sec
     seg_win_step_sec = 1.0  #: step for segmentation, in sec
diff --git a/sqi.py b/sqi.py
index 35d92de..d643e8b 100644
--- a/sqi.py
+++ b/sqi.py
@@ -28,14 +28,14 @@ class SigQuality:
 
     def __init__(self): pass
 
-    def get_snr(self, fs, ssf, ssf_threshold, ssf_zxings):
+    def get_snr(self, fs, ssf, ssf_threshold, est_zxings):
         """Compute the Signal-to-Noise Ratio of beats, based on SSF function and detected beat locations."""
         sigma = fs * self.gauss_beat_template_sigma_sec
         W = int(fs * self.gauss_beat_template_win_sec)
         gb = gauss(W, W//2, sigma)
         # place gaussians on estimated beat locations
         ssf_est = np.zeros(ssf.shape[0])
-        for i in ssf_zxings:
+        for i in est_zxings:
             ssf_est += shift(ssf.shape[0], i, gb)
         ssf_est /= gb[W//2]  # normalize amplitude to 1.0
         ssf_est = np.roll(ssf_est, int(sigma))  # shift to right (beat loc = gauss beginning, not center)
@@ -49,7 +49,7 @@ class SigQuality:
         sqi_noise = np.sum(sqi_pen * (ssf**2))
 
         # noise is everywhere, while signal is only around detected peaks - correct for this.
-        goal_density = np.mean(np.clip(2*sigma / np.diff(ssf_zxings), a_min=0, a_max=1))
+        goal_density = np.mean(np.clip(2*sigma / np.diff(est_zxings), a_min=0, a_max=1))
         sqi_goal /= goal_density
         sqi = 10 * (np.log10(sqi_goal) - np.log10(sqi_noise))