diff --git a/main.cpp b/main.cpp
index 4839a9e..d08c26c 100644
--- a/main.cpp
+++ b/main.cpp
@@ -3061,13 +3061,16 @@ int run(const Config& cfg) {
                                     !tty_do1_pair_state.pending_ch1_di8_high && !di8_level;
 
                                 if (pair_di1_matches && pair_di2_matches) {
-                                    if (both_di8_high) {
-                                        tty_di8_state.add_sample(0U, tty_do1_pair_state.pending_ch1_raw);
-                                        tty_di8_state.add_sample(1U, adc_raw_value);
-                                        ++packet_di8_samples_accumulated;
-                                        ++packet_di8_both_high;
-                                    } else if (both_di8_normal) {
-                                        ++packet_di8_both_normal;
+                                    if (!both_di8_high && !both_di8_normal) {
+                                        ++packet_di8_mixed;  // mixed DI8 pair -- discard
+                                    } else {
+                                        if (both_di8_high) {
+                                            ++packet_di8_both_high;
+                                        } else {
+                                            ++packet_di8_both_normal;
+                                        }
+
+                                        // DO1 transition detection (ALL non-mixed pairs).
                                         if (!tty_do1_pair_state.run_initialized) {
                                             tty_do1_pair_state.start_run(di1_level);
                                         } else if (tty_do1_pair_state.run_di1_high != di1_level) {
@@ -3076,11 +3079,20 @@ int run(const Config& cfg) {
                                             tty_do1_pair_state.start_run(di1_level);
                                         }
 
+                                        // DI8=HIGH accumulation AFTER transition check so emitted
+                                        // di8_ref_step belongs to the completed run, not the new one.
+                                        if (both_di8_high) {
+                                            tty_di8_state.add_sample(0U, tty_do1_pair_state.pending_ch1_raw);
+                                            tty_di8_state.add_sample(1U, adc_raw_value);
+                                            ++packet_di8_samples_accumulated;
+                                        }
+
+                                        // Pair subtraction includes ALL non-mixed pairs (both
+                                        // DI8=HIGH and DI8=LOW) so DO1 transitions stay visible
+                                        // even when DO8 and DO1 phases are perfectly aligned.
                                         tty_do1_pair_state.add_pair_sample(di2_level,
                                                                            tty_do1_pair_state.pending_ch1_raw,
                                                                            adc_raw_value);
-                                    } else {
-                                        ++packet_di8_mixed;  // mixed DI8 pair -- discard
                                     }
                                 }
                             }
diff --git a/run_do8_freq_ref.sh b/run_do8_freq_ref.sh
index e03ef2d..e53a291 100755
--- a/run_do8_freq_ref.sh
+++ b/run_do8_freq_ref.sh
@@ -30,6 +30,6 @@ exec "$BIN" \
   do1_toggle_per_frame \
   do1_pair_subtract_avg \
   do8_freq_ref \
-  do8_cycle_period:8 \
+  do8_cycle_period:4 \
   "tty:${TTY_PATH}" \
   "$@"