X-Git-Url: https://main.carlh.net/gitweb/?a=blobdiff_plain;f=libs%2Fardour%2Fsession_ltc.cc;h=8d976ea4da1b35814c9fd1a76174b82021571d6a;hb=0a4f4026a9e98ad2466d7f3e7de41dac8f22a136;hp=d14756c0ba063e524fc68d0b6cd610a1d1fbe40a;hpb=52532839110d4bbd2e4dc3e0eb8967d0f278a611;p=ardour.git

diff --git a/libs/ardour/session_ltc.cc b/libs/ardour/session_ltc.cc
index d14756c0ba..8d976ea4da 100644
--- a/libs/ardour/session_ltc.cc
+++ b/libs/ardour/session_ltc.cc
@@ -39,6 +39,25 @@ using namespace Timecode;
 //#define LTC_GEN_FRAMEDBUG
 //#define LTC_GEN_TXDBUG
 
+#ifndef MAX
+#define MAX(a,b) ( (a) > (b) ? (a) : (b) )
+#endif
+#ifndef MIN
+#define MIN(a,b) ( (a) < (b) ? (a) : (b) )
+#endif
+
+/* LTC signal should have a rise time of 25 us +/- 5 us.
+ * yet with most sound-cards a square-wave of 1-2 sample
+ * introduces rather some ringing and small oscillations.
+ * so we low-pass filter the signal a bit, depending
+ * on the sample-rate.
+ *
+ * TODO: this should become an adaptive value, when
+ * the playback speed is increases so that 1 bit < 3-4
+ * audio samples, we should fall back to 25 us.
+ */
+#define LTC_RISE_TIME MIN (100, MAX(25, (2000000 / engine().frame_rate())))
+
 void
 Session::ltc_tx_initialize()
 {
@@ -50,6 +69,7 @@ Session::ltc_tx_initialize()
 			0);
 
 	ltc_encoder_set_bufsize(ltc_encoder, nominal_frame_rate(), 23.0);
+	ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME);
 
 	/* buffersize for 1 LTC frame: (1 + sample-rate / fps) bytes
 	 * usually returned by ltc_encoder_get_buffersize(encoder)
@@ -153,19 +173,6 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
 	/* range from libltc (38..218) || - 128.0  -> (-90..90) */
 	const float ltcvol = Config->get_ltc_output_volume()/(90.0); // pow(10, db/20.0)/(90.0);
 
-#if 1
-	/* TODO read layency only on demand -> ::ltc_tx_reset()
-	 * this is already prepared.
-	 *
-	 * ..but first fix jack2 issue with re-computing latency
-	 * in the correct order. Until then, querying it in the
-	 * process-callback is the only way to get the current value
-	 *
-	 * update: fix for this issue is known -- common/JackEngine.cpp
-	 * but not yet applied to jack2 git.
-	 */
-	ltcport->get_connected_latency_range(ltc_out_latency, true);
-#endif
 	DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX %1 to %2 / %3 | lat: %4\n", start_frame, end_frame, nframes, ltc_out_latency.max));
 
 	/* all systems go. Now here's the plan:
@@ -191,6 +198,9 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
 			ltc_tx_cleanup();
 			return;
 		}
+		if (nominal_frame_rate() <= 48000) {
+			ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME);
+		}
 		ltc_enc_tcformat = cur_timecode;
 		ltc_tx_reset();
 	}
@@ -208,18 +218,11 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
 #define SIGNUM(a) ( (a) < 0 ? -1 : 1)
 	bool speed_changed = false;
 
-	/* use port latency compensation */
-#if 1
-	/* The generated timecode is offset by the port-latency,
+	/* port latency compensation:
+	 * The _generated timecode_ is offset by the port-latency,
 	 * therefore the offset depends on the direction of transport.
 	 */
-	framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame + ltc_out_latency.max) : (start_frame - ltc_out_latency.max);
-#else
-	/* This comes in handy when testing sync - record output on an A3 track
-	 * see also http://tracker.ardour.org/view.php?id=5073
-	 */
-	framepos_t cycle_start_frame = start_frame;
-#endif
+	framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame - ltc_out_latency.max) : (start_frame + ltc_out_latency.max);
 
 	/* cycle-start may become negative due to latency compensation */
 	if (cycle_start_frame < 0) { cycle_start_frame = 0; }
@@ -466,6 +469,24 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
 		DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 |  byte %4\n",
 					ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
 	}
+#if 1 /* experimental sample bit alignment */
+	else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
+		/* We may get away without a DLL if speed-changes are uniform enough and
+		 * no oscillation takes place, the linear approx here should reduce the
+		 * jitter sufficiently when generating LTC from another LTC source or
+		 * JACK-transport or ardour internal clock.
+		 *
+		 * Note that the granularity of the LTC encoder speed is 1 byte =
+		 * (frames-per-timecode-frame / 10) audio-samples.
+		 *
+		 * Thus, tiny speed changes won't have any effect and larger ones
+		 * may lead to oscillations.
+		 * To be better than that, resampling (or a rewrite of the encoder) is
+		 * required.
+		 */
+		ltc_speed -= ((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) / engine().frame_rate();
+	}
+#endif
 
 
 	// (6) encode and output
@@ -530,6 +551,12 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
 			ltc_enc_byte = (ltc_enc_byte + 1)%10;
 			if (ltc_enc_byte == 0 && ltc_speed != 0) {
 				ltc_encoder_inc_timecode(ltc_encoder);
+#if 0 /* force fixed parity -- scope debug */
+				LTCFrame f;
+				ltc_encoder_get_frame(ltc_encoder, &f);
+				f.biphase_mark_phase_correction=0;
+				ltc_encoder_set_frame(ltc_encoder, &f);
+#endif
 				ltc_tx_recalculate_position();
 				ltc_enc_cnt = 0;
 			} else if (ltc_enc_byte == 0) {