Allow to configure vari-speed resampler quality

This also allows to disable the resampler, effectively disabling
varispeed support, for the benefit of adding no additional latency.
By default 2 * 16 samples latency are added, due to port-resampler,
this is not desirable if Ardour is used as mixer only.

libs/ardour/ardour/port.h

@@ -158,7 +158,11 @@ public:
 
 	static pframes_t cycle_nframes () { return _cycle_nframes; }
 	static double speed_ratio () { return _speed_ratio; }
+
 	static uint32_t resampler_quality () { return _resampler_quality; }
+	static uint32_t resampler_latency () { return _resampler_latency; }
+	static bool     can_varispeed ()     { return _resampler_latency > 0; }
+	static void     setup_resampler (uint32_t q = 17);
 
 protected:
 
@@ -175,7 +179,6 @@ protected:
 	LatencyRange _private_capture_latency;
 
 	static double _speed_ratio;
-	static const uint32_t _resampler_quality; /* also latency of the resampler */
 
 private:
 	std::string _name;  ///< port short name
@@ -188,6 +191,9 @@ private:
 	*/
 	std::set<std::string> _connections;
 
+	static uint32_t _resampler_quality; // 8 <= q <= 96
+	static uint32_t _resampler_latency; // = _resampler_quality - 1
+
 	void port_connected_or_disconnected (boost::weak_ptr<Port>, boost::weak_ptr<Port>, bool);
 	void signal_drop ();
 	void session_global_drop ();

libs/ardour/ardour/rc_configuration_vars.h

@@ -40,6 +40,9 @@ CONFIG_VARIABLE (AutoConnectOption, output_auto_connect, "output-auto-connect",
 CONFIG_VARIABLE (AutoConnectOption, input_auto_connect, "input-auto-connect", AutoConnectPhysical)
 CONFIG_VARIABLE (bool, strict_io, "strict-io", true)
 
+/* 0: off, no varispeed, q: 8..96 */
+CONFIG_VARIABLE (uint32_t, port_resampler_quality, "port-resampler-quality,", 17)
+
 /* Connect all physical inputs to a dummy port, this makes raw input data available.
  * `jack_port_get_buffer (jack_port_by_name (c, "system:capture_1") , n_samples);`
  * nees to work for input-monitoring (recorder page).

libs/ardour/audio_port.cc

@@ -42,7 +42,7 @@ AudioPort::AudioPort (const std::string& name, PortFlags flags)
 	, _data (0)
 {
 	assert (name.find_first_of (':') == string::npos);
-	_src.setup (_resampler_quality);
+	_src.setup (resampler_quality ());
 	_src.set_rrfilt (10);
 }
 

libs/ardour/disk_writer.cc

@@ -699,9 +699,9 @@ DiskWriter::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_samp
 		}
 
 		if (_xrun_flag) {
-			/* There still are `Port::resampler_quality () -1` samples in the resampler
+			/* There still are `Port::resampler_latency ()` samples in the resampler
 			 * buffer from before the xrun. */
-			_xruns.push_back (_capture_captured + Port::resampler_quality () - 1);
+			_xruns.push_back (_capture_captured + Port::resampler_latency ());
 		}
 
 		_capture_captured += rec_nframes;

libs/ardour/globals.cc

@@ -613,6 +613,8 @@ ARDOUR::init (bool try_optimization, const char* localedir, bool with_gui)
 	}
 #endif
 
+	Port::setup_resampler (Config->get_port_resampler_quality ());
+
 	setup_hardware_optimization (try_optimization);
 
 	if (Config->get_cpu_dma_latency () >= 0) {

libs/ardour/port.cc

@@ -47,7 +47,8 @@ pframes_t    Port::_global_port_buffer_offset = 0;
 pframes_t    Port::_cycle_nframes = 0;
 double       Port::_speed_ratio = 1.0;
 std::string  Port::state_node_name = X_("Port");
-const uint32_t Port::_resampler_quality = 17;
+uint32_t     Port::_resampler_quality = 17;
+uint32_t     Port::_resampler_latency = 16; // = _resampler_quality - 1;
 
 /* a handy define to shorten what would otherwise be a needlessly verbose
  * repeated phrase
@@ -388,13 +389,9 @@ Port::set_public_latency_range (LatencyRange const& range, bool playback) const
 	if (_port_handle) {
 		LatencyRange r (range);
 		if (externally_connected () && 0 == (_flags & TransportSyncPort) && sends_output () == playback) {
-#if 0
-			r.min *= _speed_ratio;
-			r.max *= _speed_ratio;
-#endif
 			if (type () == DataType::AUDIO) {
-				r.min += (_resampler_quality - 1);
-				r.max += (_resampler_quality - 1);
+				r.min += (_resampler_latency);
+				r.max += (_resampler_latency);
 			}
 		}
 		port_engine.set_latency_range (_port_handle, playback, r);
@@ -449,19 +446,6 @@ Port::public_latency_range (bool playback) const
 
 	if (_port_handle) {
 		r = port_engine.get_latency_range (_port_handle, playback);
-		if (externally_connected () && 0 == (_flags & TransportSyncPort) && sends_output () == playback) {
-#if 0
-			r.min /= _speed_ratio;
-			r.max /= _speed_ratio;
-#endif
-#if 0
-			/* use value as set by set_public_latency_range */
-			if (type () == DataType::AUDIO) {
-				r.min += (_resampler_quality - 1);
-				r.max += (_resampler_quality - 1);
-			}
-#endif
-		}
 
 		DEBUG_TRACE (DEBUG::LatencyIO, string_compose (
 				     "GET PORT %1: %4 PUBLIC latency range %2 .. %3\n",
@@ -493,8 +477,8 @@ Port::collect_latency_from_backend (LatencyRange& range, bool playback) const
 		if (!AudioEngine::instance()->port_is_mine (*c)) {
 			if (externally_connected () && 0 == (_flags & TransportSyncPort) && sends_output () == playback) {
 				if (type () == DataType::AUDIO) {
-					lr.min += (_resampler_quality - 1);
-					lr.max += (_resampler_quality - 1);
+					lr.min += (_resampler_latency);
+					lr.max += (_resampler_latency);
 				}
 			}
 		}
@@ -542,13 +526,9 @@ Port::get_connected_latency_range (LatencyRange& range, bool playback) const
 				if (remote_port) {
 					lr = port_engine.get_latency_range (remote_port, playback);
 					if (externally_connected () && 0 == (_flags & TransportSyncPort) && sends_output () == playback) {
-#if 0
-						lr.min /= _speed_ratio;
-						lr.max /= _speed_ratio;
-#endif
 						if (type () == DataType::AUDIO) {
-							lr.min += (_resampler_quality - 1);
-							lr.max += (_resampler_quality - 1);
+							lr.min += (_resampler_latency);
+							lr.max += (_resampler_latency);
 						}
 					}
 
@@ -726,13 +706,40 @@ Port::set_state (const XMLNode& node, int)
 	return 0;
 }
 
+/* static */ void
+Port::setup_resampler (uint32_t q)
+{
+	/* configure at application start (Ardour::init) */
+	static bool setup_done = false;
+	if (setup_done) {
+		return;
+	}
+	setup_done = true;
+	if (q == 0) {
+		/* no vari-speed */
+		_resampler_quality = 0;
+		_resampler_latency = 0;
+		return;
+	}
+	// range constrained in VMResampler::setup
+	if (q < 8) {
+		q = 8;
+	}
+	if (q > 96) {
+		q = 96;
+	}
+	_resampler_quality = q;
+	_resampler_latency = q - 1;
+}
+
+
 /*static*/ void
 Port::set_speed_ratio (double s) {
-	/* see VMResampler::set_rratio() for min/max range */
-	if (s == 0.0) {
+	if (s == 0.0 || !can_varispeed ()) {
 		/* no resampling when stopped */
 		_speed_ratio = 1.0;
 	} else {
+		/* see VMResampler::set_rratio() for min/max range */
 		_speed_ratio = std::min ((double) Config->get_max_transport_speed(), std::max (0.02, fabs (s)));
 	}
 }