Prepare to filter incoming LTC

libs/ardour/ardour/transport_master.h

@@ -613,7 +613,7 @@ public:
 	void create_port ();
 
 private:
-	void parse_ltc (const pframes_t, const Sample* const, const samplecnt_t);
+	void parse_ltc (const pframes_t, Sample const*, samplecnt_t);
 	void process_ltc (samplepos_t const);
 	void init_dll (samplepos_t, int32_t);
 	bool detect_discontinuity (LTCFrameExt*, int, bool);
@@ -643,6 +643,17 @@ private:
 	PBD::ScopedConnection     port_connection;
 	PBD::ScopedConnectionList session_connections;
 	LatencyRange              ltc_slave_latency;
+
+
+	struct Biquad {
+		void reset () { z1 = z2 = 0;}
+		float  z1, z2;
+		double a1, a2, b0, b1, b2;
+	};
+
+	bool   _filter_enable;
+	Biquad _lpf;
+	Biquad _hpf;
 };
 
 class LIBARDOUR_API MIDIClock_TransportMaster : public TransportMaster, public TransportMasterViaMIDI

libs/ardour/ltc_slave.cc

@@ -27,6 +27,7 @@
 #include "pbd/pthread_utils.h"
 
 #include "ardour/debug.h"
+#include "ardour/dsp_filter.h"
 #include "ardour/profile.h"
 #include "ardour/transport_master.h"
 #include "ardour/session.h"
@@ -58,6 +59,7 @@ LTC_TransportMaster::LTC_TransportMaster (std::string const & name)
 	, ltc_detect_fps_max (0)
 	, sync_lock_broken (false)
 	, samples_per_timecode_frame (0)
+	, _filter_enable (false)
 {
 	memset (&prev_frame, 0, sizeof(LTCFrameExt));
 
@@ -97,6 +99,17 @@ LTC_TransportMaster::set_session (Session *s)
 
 		decoder = ltc_decoder_create((int) samples_per_ltc_frame, 128 /*queue size*/);
 
+		DSP::Biquad bq (AudioEngine::instance()->sample_rate());
+		bq.compute (DSP::Biquad::LowPass, 3500, 0.9, 0);
+		bq.coefficients (_lpf.a1, _lpf.a2, _lpf.b0, _lpf.b1, _lpf.b2);
+		bq.compute (DSP::Biquad::HighPass, 100, 0.707, 0);
+		bq.coefficients (_hpf.a1, _hpf.a2, _hpf.b0, _hpf.b1, _hpf.b2);
+		_lpf.reset ();
+		_hpf.reset ();
+
+		// TODO add a per master preference to enable filter (and set gain)
+		//_filter_enable = true;
+
 		parse_timecode_offset();
 		reset (true);
 
@@ -104,6 +117,8 @@ LTC_TransportMaster::set_session (Session *s)
 
 		_session->config.ParameterChanged.connect_same_thread (session_connections, boost::bind (&LTC_TransportMaster::parameter_changed, this, _1));
 		_session->LatencyUpdated.connect_same_thread (session_connections, boost::bind (&LTC_TransportMaster::resync_latency, this, _1));
+	} else {
+		_filter_enable = false;
 	}
 }
 
@@ -209,6 +224,8 @@ LTC_TransportMaster::resync_latency (bool playback)
 	if (old != ltc_slave_latency.max) {
 		sync_lock_broken = false;
 	}
+	_lpf.reset ();
+	_hpf.reset ();
 }
 
 void
@@ -231,26 +248,40 @@ LTC_TransportMaster::reset (bool with_position)
 }
 
 void
-LTC_TransportMaster::parse_ltc (const ARDOUR::pframes_t nframes, const Sample* const in, const ARDOUR::samplecnt_t posinfo)
+LTC_TransportMaster::parse_ltc (pframes_t const n_samples, Sample const* in, samplecnt_t posinfo)
 {
-	pframes_t i;
-	unsigned char sound[8192];
+	pframes_t remain = n_samples;
 
-	if (nframes > 8192) {
-		/* TODO warn once or wrap, loop conversion below
-		 * does jack/A3 support > 8192 spp anyway?
-		 */
-		return;
-	}
+	bool  const fe   = _filter_enable;
+	float const gain = 127.0; // relative to signed 8bit, 127.0 == 0dB
 
-	for (i = 0; i < nframes; i++) {
-		const int snd=(int) rint ((127.0*in[i])+128.0);
-		sound[i] = (unsigned char) (snd&0xff);
-	}
-
-	ltc_decoder_write (decoder, sound, nframes, posinfo);
-
-	return;
+	while (remain > 0) {
+    ltcsnd_sample_t sound[8192];
+    pframes_t c = std::min<pframes_t> (remain, 8192);
+		if (fe) {
+			for (pframes_t i = 0; i < c; ++i) {
+				/* LPF */
+				float xn = *in++;
+				float z  = _lpf.b0 * xn + _lpf.z1;
+				_lpf.z1  = _lpf.b1 * xn - _lpf.a1 * z + _lpf.z2;
+				_lpf.z2  = _lpf.b2 * xn - _lpf.a2 * z;
+				/* HPF */
+				xn       = z;
+				z        = _hpf.b0 * xn + _hpf.z1;
+				_hpf.z1  = _hpf.b1 * xn - _hpf.a1 * z + _hpf.z2;
+				_hpf.z2  = _hpf.b2 * xn - _hpf.a2 * z;
+				/* convert */
+				sound[i] = 128 + min (127, max<int> (-127, gain * z));
+			}
+		} else {
+			for (pframes_t i = 0; i < c; ++i) {
+				sound[i] = 128 + min (127, max<int> (-127, gain * (*in++)));
+			}
+		}
+    ltc_decoder_write (decoder, sound, c, posinfo);
+    posinfo += c;
+    remain -= c;
+  }
 }
 
 bool