Initial Gain Coefficient tweaks

1)  Disambiguate 1.0 to GAIN_COEFF_UNITY, and 0.0 to GAIN_COEFF_ZERO
2)  Add GAIN_COEFF_SMALL which replaces SMALL_SIGNAL (-140dB)
3)  GAIN_COEFF_SMALL can used to avoid interpolating towards -inf on a db scale
4)  GAIN_COEFF_SMALL is used to detect very small (denormal?) gains and memset to zero

13 files changed, 80 insertions, 78 deletions

diff --git a/libs/ardour/amp.cc b/libs/ardour/amp.cc
index 523b538359..ac970fc581 100644
--- a/libs/ardour/amp.cc
+++ b/libs/ardour/amp.cc
@@ -40,7 +40,7 @@ Amp::Amp (Session& s)
 	: Processor(s, "Amp")
 	, _apply_gain(true)
 	, _apply_gain_automation(false)
-	, _current_gain(1.0)
+	, _current_gain(GAIN_COEFF_UNITY)
 	, _current_automation_frame (INT64_MAX)
 	, _gain_automation_buffer(0)
 {
@@ -115,7 +115,7 @@ Amp::run (BufferSet& bufs, framepos_t /*start_frame*/, framepos_t /*end_frame*/,
 
 				_current_gain = Amp::apply_gain (bufs, _session.nominal_frame_rate(), nframes, _current_gain, dg);
 
-			} else if (_current_gain != 1.0f) {
+			} else if (_current_gain != GAIN_COEFF_UNITY) {
 
 				/* gain has not changed, but its non-unity
 				*/
@@ -221,11 +221,11 @@ Amp::declick (BufferSet& bufs, framecnt_t nframes, int dir)
 	if (dir < 0) {
 		/* fade out: remove more and more of delta from initial */
 		delta = -1.0;
-                initial = 1.0;
+                initial = GAIN_COEFF_UNITY;
 	} else {
 		/* fade in: add more and more of delta from initial */
 		delta = 1.0;
-                initial = 0.0;
+                initial = GAIN_COEFF_ZERO;
 	}
 
 	/* Audio Gain */
@@ -275,15 +275,15 @@ Amp::apply_gain (AudioBuffer& buf, framecnt_t sample_rate, framecnt_t nframes, g
 		lpf += a * (target - lpf);
         }
 
-	if (lpf < 1e-10) return 0;
-	if (fabsf(lpf - 1.0) < 1e-10) return 1.0;
+	if (lpf < 1e-10) return 0; // TODO use GAIN_COEFF_TINY or _DENORMAL
+	if (fabsf(lpf - GAIN_COEFF_UNITY) < 1e-10) return GAIN_COEFF_UNITY;
 	return lpf;
 }
 
 void
 Amp::apply_simple_gain (BufferSet& bufs, framecnt_t nframes, gain_t target)
 {
-	if (target == 0.0) {
+	if (target < GAIN_COEFF_SMALL) {
 
 		for (BufferSet::midi_iterator i = bufs.midi_begin(); i != bufs.midi_end(); ++i) {
 			MidiBuffer& mb (*i);
@@ -300,7 +300,7 @@ Amp::apply_simple_gain (BufferSet& bufs, framecnt_t nframes, gain_t target)
 			memset (i->data(), 0, sizeof (Sample) * nframes);
 		}
 
-	} else if (target != 1.0) {
+	} else if (target != GAIN_COEFF_UNITY) {
 
 		for (BufferSet::midi_iterator i = bufs.midi_begin(); i != bufs.midi_end(); ++i) {
 			MidiBuffer& mb (*i);
@@ -322,9 +322,9 @@ Amp::apply_simple_gain (BufferSet& bufs, framecnt_t nframes, gain_t target)
 void
 Amp::apply_simple_gain (AudioBuffer& buf, framecnt_t nframes, gain_t target)
 {
-	if (target == 0.0) {
+	if (target < GAIN_COEFF_SMALL) {
                 memset (buf.data(), 0, sizeof (Sample) * nframes);
-	} else if (target != 1.0) {
+	} else if (target != GAIN_COEFF_UNITY) {
                 apply_gain_to_buffer (buf.data(), nframes, target);
 	}
 }
@@ -334,7 +334,7 @@ Amp::inc_gain (gain_t factor, void *src)
 {
 	float desired_gain = _gain_control->user_double();
 
-	if (desired_gain == 0.0f) {
+	if (desired_gain < GAIN_COEFF_SMALL) {
 		set_gain (0.000001f + (0.000001f * factor), src);
 	} else {
 		set_gain (desired_gain + (desired_gain * factor), src);
diff --git a/libs/ardour/ardour/dB.h b/libs/ardour/ardour/dB.h
index abacdfcd29..0fd75a869f 100644
--- a/libs/ardour/ardour/dB.h
+++ b/libs/ardour/ardour/dB.h
@@ -22,6 +22,10 @@
 
 #include "pbd/fastlog.h"
 
+#define GAIN_COEFF_ZERO 0.0
+#define GAIN_COEFF_SMALL 0.0000001  //-140dB
+#define GAIN_COEFF_UNITY 1.0
+
 static inline float dB_to_coefficient (float dB) {
 	return dB > -318.8f ? pow (10.0f, dB * 0.05f) : 0.0f;
 }
diff --git a/libs/ardour/audio_track.cc b/libs/ardour/audio_track.cc
index 62109e86c7..33a5ba8f37 100644
--- a/libs/ardour/audio_track.cc
+++ b/libs/ardour/audio_track.cc
@@ -603,7 +603,7 @@ AudioTrack::freeze_me (InterThreadInfo& itt)
 
 	/* reset stuff that has already been accounted for in the freeze process */
 
-	set_gain (1.0, this);
+	set_gain (GAIN_COEFF_UNITY, this);
 	_amp->gain_control()->set_automation_state (Off);
 	/* XXX need to use _main_outs _panner->set_automation_state (Off); */
 
diff --git a/libs/ardour/audioengine.cc b/libs/ardour/audioengine.cc
index 116b99085b..c70a48725a 100644
--- a/libs/ardour/audioengine.cc
+++ b/libs/ardour/audioengine.cc
@@ -283,7 +283,7 @@ AudioEngine::process_callback (pframes_t nframes)
 
 			/* fade out over 1 second */
 			session_removal_countdown = sample_rate()/2;
-			session_removal_gain = 1.0;
+			session_removal_gain = GAIN_COEFF_UNITY;
 			session_removal_gain_step = 1.0/session_removal_countdown;
 
 		} else if (session_removal_countdown > 0) {
diff --git a/libs/ardour/audioregion.cc b/libs/ardour/audioregion.cc
index 37bf3e1fed..026de0713b 100644
--- a/libs/ardour/audioregion.cc
+++ b/libs/ardour/audioregion.cc
@@ -72,8 +72,6 @@ namespace ARDOUR {
 	}
 }
 
-static const double VERY_SMALL_SIGNAL = 0.0000001;  //-140dB
-
 /* Curve manipulations */
 
 static void
@@ -106,14 +104,14 @@ generate_db_fade (boost::shared_ptr<Evoral::ControlList> dst, double len, int nu
 	//generate a fade-out curve by successively applying a gain drop
 	float fade_speed = dB_to_coefficient(dB_drop / (float) num_steps);
 	for (int i = 1; i < (num_steps-1); i++) {
-		float coeff = 1.0;
+		float coeff = GAIN_COEFF_UNITY;
 		for (int j = 0; j < i; j++) {
 			coeff *= fade_speed;
 		}
 		dst->fast_simple_add (len*(double)i/(double)num_steps, coeff);
 	}
 
-	dst->fast_simple_add (len, VERY_SMALL_SIGNAL);
+	dst->fast_simple_add (len, GAIN_COEFF_SMALL);
 }
 
 static void
@@ -791,8 +789,8 @@ AudioRegion::state ()
 	// so, if they are both at 1.0f, that means the default region.
 
 	if (_envelope->size() == 2 &&
-	    _envelope->front()->value == 1.0f &&
-	    _envelope->back()->value==1.0f) {
+	    _envelope->front()->value == GAIN_COEFF_UNITY &&
+	    _envelope->back()->value==GAIN_COEFF_UNITY) {
 		if (_envelope->front()->when == 0 && _envelope->back()->when == _length) {
 			default_env = true;
 		}
@@ -1026,8 +1024,8 @@ AudioRegion::set_fade_in (FadeShape shape, framecnt_t len)
 
 	switch (shape) {
 	case FadeLinear:
-		_fade_in->fast_simple_add (0.0, VERY_SMALL_SIGNAL);
-		_fade_in->fast_simple_add (len, 1.0);
+		_fade_in->fast_simple_add (0.0, GAIN_COEFF_SMALL);
+		_fade_in->fast_simple_add (len, GAIN_COEFF_UNITY);
 		reverse_curve (_inverse_fade_in.val(), _fade_in.val());
 		break;
 
@@ -1048,12 +1046,12 @@ AudioRegion::set_fade_in (FadeShape shape, framecnt_t len)
 		break;
 
 	case FadeConstantPower:
-		_fade_in->fast_simple_add (0.0, VERY_SMALL_SIGNAL);
+		_fade_in->fast_simple_add (0.0, GAIN_COEFF_SMALL);
 		for (int i = 1; i < num_steps; ++i) {
 			const float dist = i / (num_steps + 1.f);
 			_fade_in->fast_simple_add (len * dist, sin (dist * M_PI / 2.0));
 		}
-		_fade_in->fast_simple_add (len, 1.0);
+		_fade_in->fast_simple_add (len, GAIN_COEFF_UNITY);
 		reverse_curve (_inverse_fade_in.val(), _fade_in.val());
 		break;
 		
@@ -1065,9 +1063,9 @@ AudioRegion::set_fade_in (FadeShape shape, framecnt_t len)
 		const double breakpoint = 0.7;  //linear for first 70%
 		for (int i = 2; i < 9; ++i) {
 			const float coeff = (1.f - breakpoint) * powf (0.5, i);
-			_fade_in->fast_simple_add (len * (breakpoint + ((1.0 - breakpoint) * (double)i / 9.0)), coeff);
+			_fade_in->fast_simple_add (len * (breakpoint + ((GAIN_COEFF_UNITY - breakpoint) * (double)i / 9.0)), coeff);
 		}
-		_fade_in->fast_simple_add (len, VERY_SMALL_SIGNAL);
+		_fade_in->fast_simple_add (len, GAIN_COEFF_SMALL);
 		reverse_curve (c3, _fade_in.val());
 		_fade_in->copy_events (*c3);
 		reverse_curve (_inverse_fade_in.val(), _fade_in.val());
@@ -1108,8 +1106,8 @@ AudioRegion::set_fade_out (FadeShape shape, framecnt_t len)
 
 	switch (shape) {
 	case FadeLinear:
-		_fade_out->fast_simple_add (0.0, 1.0);
-		_fade_out->fast_simple_add (len, VERY_SMALL_SIGNAL);
+		_fade_out->fast_simple_add (0.0, GAIN_COEFF_UNITY);
+		_fade_out->fast_simple_add (len, GAIN_COEFF_SMALL);
 		reverse_curve (_inverse_fade_out.val(), _fade_out.val());
 		break;
 		
@@ -1128,12 +1126,12 @@ AudioRegion::set_fade_out (FadeShape shape, framecnt_t len)
 	case FadeConstantPower:
 		//constant-power fades use a sin/cos relationship
 		//the cutoff is abrupt but it has the benefit of being symmetrical
-		_fade_out->fast_simple_add (0.0, 1.0);
+		_fade_out->fast_simple_add (0.0, GAIN_COEFF_UNITY);
 		for (int i = 1; i < num_steps; ++i) {
 			const float dist = i / (num_steps + 1.f);
 			_fade_out->fast_simple_add (len * dist, cos (dist * M_PI / 2.0));
 		}
-		_fade_out->fast_simple_add (len, VERY_SMALL_SIGNAL);
+		_fade_out->fast_simple_add (len, GAIN_COEFF_SMALL);
 		reverse_curve (_inverse_fade_out.val(), _fade_out.val());
 		break;
 		
@@ -1145,9 +1143,9 @@ AudioRegion::set_fade_out (FadeShape shape, framecnt_t len)
 		const double breakpoint = 0.7;  //linear for first 70%
 		for (int i = 2; i < 9; ++i) {
 			const float coeff = (1.f - breakpoint) * powf (0.5, i);
-			_fade_out->fast_simple_add (len * (breakpoint + ((1.0 - breakpoint) * (double)i / 9.0)), coeff);
+			_fade_out->fast_simple_add (len * (breakpoint + ((GAIN_COEFF_UNITY - breakpoint) * (double)i / 9.0)), coeff);
 		}
-		_fade_out->fast_simple_add (len, VERY_SMALL_SIGNAL);
+		_fade_out->fast_simple_add (len, GAIN_COEFF_SMALL);
 		reverse_curve (_inverse_fade_out.val(), _fade_out.val());
 		break;
 	}
@@ -1266,8 +1264,8 @@ AudioRegion::set_default_envelope ()
 {
 	_envelope->freeze ();
 	_envelope->clear ();
-	_envelope->fast_simple_add (0, 1.0f);
-	_envelope->fast_simple_add (_length, 1.0f);
+	_envelope->fast_simple_add (0, GAIN_COEFF_UNITY);
+	_envelope->fast_simple_add (_length, GAIN_COEFF_UNITY);
 	_envelope->thaw ();
 }
 
@@ -1447,14 +1445,14 @@ AudioRegion::normalize (float max_amplitude, float target_dB)
 {
 	gain_t target = dB_to_coefficient (target_dB);
 
-	if (target == 1.0f) {
+	if (target == GAIN_COEFF_UNITY) {
 		/* do not normalize to precisely 1.0 (0 dBFS), to avoid making it appear
 		   that we may have clipped.
 		*/
 		target -= FLT_EPSILON;
 	}
 
-	if (max_amplitude == 0.0f) {
+	if (max_amplitude < GAIN_COEFF_SMALL) {
 		/* don't even try */
 		return;
 	}
diff --git a/libs/ardour/delivery.cc b/libs/ardour/delivery.cc
index f16719888f..359b029d0c 100644
--- a/libs/ardour/delivery.cc
+++ b/libs/ardour/delivery.cc
@@ -52,7 +52,7 @@ Delivery::Delivery (Session& s, boost::shared_ptr<IO> io, boost::shared_ptr<Pann
 	: IOProcessor(s, boost::shared_ptr<IO>(), (role_requires_output_ports (r) ? io : boost::shared_ptr<IO>()), name)
 	, _role (r)
 	, _output_buffers (new BufferSet())
-	, _current_gain (1.0)
+	, _current_gain (GAIN_COEFF_UNITY)
 	, _no_outs_cuz_we_no_monitor (false)
 	, _mute_master (mm)
 	, _no_panner_reset (false)
@@ -76,7 +76,7 @@ Delivery::Delivery (Session& s, boost::shared_ptr<Pannable> pannable, boost::sha
 	: IOProcessor(s, false, (role_requires_output_ports (r) ? true : false), name, "", DataType::AUDIO, (r == Send))
 	, _role (r)
 	, _output_buffers (new BufferSet())
-	, _current_gain (1.0)
+	, _current_gain (GAIN_COEFF_UNITY)
 	, _no_outs_cuz_we_no_monitor (false)
 	, _mute_master (mm)
 	, _no_panner_reset (false)
@@ -264,7 +264,7 @@ Delivery::run (BufferSet& bufs, framepos_t start_frame, framepos_t end_frame, pf
 
 		_current_gain = Amp::apply_gain (bufs, _session.nominal_frame_rate(), nframes, _current_gain, tgain);
 
-	} else if (tgain == 0.0) {
+	} else if (tgain < GAIN_COEFF_SMALL) {
 
 		/* we were quiet last time, and we're still supposed to be quiet.
 		   Silence the outputs, and make sure the buffers are quiet too,
@@ -273,11 +273,11 @@ Delivery::run (BufferSet& bufs, framepos_t start_frame, framepos_t end_frame, pf
 		_output->silence (nframes);
 		if (result_required) {
 			bufs.set_count (output_buffers().count ());
-			Amp::apply_simple_gain (bufs, nframes, 0.0);
+			Amp::apply_simple_gain (bufs, nframes, GAIN_COEFF_ZERO);
 		}
 		goto out;
 
-	} else if (tgain != 1.0) {
+	} else if (tgain != GAIN_COEFF_UNITY) {
 
 		/* target gain has not changed, but is not unity */
 		Amp::apply_simple_gain (bufs, nframes, tgain);
@@ -498,7 +498,7 @@ Delivery::target_gain ()
 	/* if we've been requested to deactivate, our target gain is zero */
 
 	if (!_pending_active) {
-		return 0.0;
+		return GAIN_COEFF_ZERO;
 	}
 
 	/* if we've been told not to output because its a monitoring situation and
@@ -506,7 +506,7 @@ Delivery::target_gain ()
 	*/
 
 	if (_no_outs_cuz_we_no_monitor) {
-		return 0.0;
+		return GAIN_COEFF_ZERO;
 	}
 
         MuteMaster::MutePoint mp = MuteMaster::Main; // stupid gcc uninit warning
@@ -538,7 +538,7 @@ Delivery::target_gain ()
                    it gets its signal from the master out.
                 */
 
-                desired_gain = 0.0;
+                desired_gain = GAIN_COEFF_ZERO;
 
         }
 
diff --git a/libs/ardour/export_format_specification.cc b/libs/ardour/export_format_specification.cc
index 7e41b209a4..32d16c9dee 100644
--- a/libs/ardour/export_format_specification.cc
+++ b/libs/ardour/export_format_specification.cc
@@ -167,7 +167,7 @@ ExportFormatSpecification::ExportFormatSpecification (Session & s)
 	, _silence_end (s)
 
 	, _normalize (false)
-	, _normalize_target (1.0)
+	, _normalize_target (GAIN_COEFF_UNITY)
 	, _with_toc (false)
 	, _with_cue (false)
 	, _with_mp4chaps (false)
diff --git a/libs/ardour/internal_send.cc b/libs/ardour/internal_send.cc
index de5af0c6e2..e8e560c7c0 100644
--- a/libs/ardour/internal_send.cc
+++ b/libs/ardour/internal_send.cc
@@ -74,10 +74,10 @@ InternalSend::init_gain ()
 {
 	if (_role == Listen) {
 		/* send to monitor bus is always at unity */
-		_amp->set_gain (1.0, this);
+		_amp->set_gain (GAIN_COEFF_UNITY, this);
 	} else {
 		/* aux sends start at -inf dB */
-		_amp->set_gain (0, this);
+		_amp->set_gain (GAIN_COEFF_ZERO, this);
 	}
 }
 
@@ -196,16 +196,16 @@ InternalSend::run (BufferSet& bufs, framepos_t start_frame, framepos_t end_frame
 
 		_current_gain = Amp::apply_gain (mixbufs, _session.nominal_frame_rate(), nframes, _current_gain, tgain);
 
-	} else if (tgain == 0.0) {
+	} else if (tgain == GAIN_COEFF_ZERO) {
 
 		/* we were quiet last time, and we're still supposed to be quiet.
 		*/
 
 		_meter->reset ();
-		Amp::apply_simple_gain (mixbufs, nframes, 0.0);
+		Amp::apply_simple_gain (mixbufs, nframes, GAIN_COEFF_ZERO);
 		goto out;
 
-	} else if (tgain != 1.0) {
+	} else if (tgain != GAIN_COEFF_UNITY) {
 
 		/* target gain has not changed, but is not zero or unity */
 		Amp::apply_simple_gain (mixbufs, nframes, tgain);
@@ -220,7 +220,7 @@ InternalSend::run (BufferSet& bufs, framepos_t start_frame, framepos_t end_frame
 	/* consider metering */
 
 	if (_metering) {
-		if (_amp->gain_control()->get_value() == 0) {
+		if (_amp->gain_control()->get_value() == GAIN_COEFF_ZERO) {
 			_meter->reset();
 		} else {
 			_meter->run (mixbufs, start_frame, end_frame, nframes, true);
diff --git a/libs/ardour/monitor_processor.cc b/libs/ardour/monitor_processor.cc
index f19ce908ec..70e4ed52c4 100644
--- a/libs/ardour/monitor_processor.cc
+++ b/libs/ardour/monitor_processor.cc
@@ -182,9 +182,9 @@ MonitorProcessor::set_state (const XMLNode& node, int version)
 
                         if ((prop = (*i)->property ("cut")) != 0) {
                                 if (string_is_affirmative (prop->value())){
-                                        cr.cut = 0.0f;
+                                        cr.cut = GAIN_COEFF_ZERO;
                                 } else {
-                                        cr.cut = 1.0f;
+                                        cr.cut = GAIN_COEFF_UNITY;
                                 }
                         }
 
@@ -256,8 +256,8 @@ MonitorProcessor::state (bool full)
                 snprintf (buf, sizeof (buf), "%u", chn);
                 chn_node->add_property ("id", buf);
 
-                chn_node->add_property (X_("cut"), (*x)->cut == 1.0f ? "no" : "yes");
-                chn_node->add_property (X_("invert"), (*x)->polarity == 1.0f ? "no" : "yes");
+                chn_node->add_property (X_("cut"), (*x)->cut == GAIN_COEFF_UNITY ? "no" : "yes");
+                chn_node->add_property (X_("invert"), (*x)->polarity == GAIN_COEFF_UNITY ? "no" : "yes");
                 chn_node->add_property (X_("dim"), (*x)->dim ? "yes" : "no");
                 chn_node->add_property (X_("solo"), (*x)->soloed ? "yes" : "no");
 
@@ -273,21 +273,21 @@ MonitorProcessor::run (BufferSet& bufs, framepos_t /*start_frame*/, framepos_t /
         uint32_t chn = 0;
         gain_t target_gain;
         gain_t dim_level_this_time = _dim_level;
-        gain_t global_cut = (_cut_all ? 0.0f : 1.0f);
-        gain_t global_dim = (_dim_all ? dim_level_this_time : 1.0);
+        gain_t global_cut = (_cut_all ? GAIN_COEFF_ZERO : GAIN_COEFF_UNITY);
+        gain_t global_dim = (_dim_all ? dim_level_this_time : GAIN_COEFF_UNITY);
         gain_t solo_boost;
 
         if (_session.listening() || _session.soloing()) {
                 solo_boost = _solo_boost_level;
         } else {
-                solo_boost = 1.0;
+                solo_boost = GAIN_COEFF_UNITY;
         }
 
         for (BufferSet::audio_iterator b = bufs.audio_begin(); b != bufs.audio_end(); ++b) {
 
                 /* don't double-scale by both track dim and global dim coefficients */
 
-                gain_t dim_level = (global_dim == 1.0 ? (_channels[chn]->dim ? dim_level_this_time : 1.0) : 1.0);
+                gain_t dim_level = (global_dim == GAIN_COEFF_UNITY ? (_channels[chn]->dim ? dim_level_this_time : GAIN_COEFF_UNITY) : GAIN_COEFF_UNITY);
 		
                 if (_channels[chn]->soloed) {
                         target_gain = _channels[chn]->polarity * _channels[chn]->cut * dim_level * global_cut * global_dim * solo_boost;
@@ -295,11 +295,11 @@ MonitorProcessor::run (BufferSet& bufs, framepos_t /*start_frame*/, framepos_t /
                         if (solo_cnt == 0) {
                                 target_gain = _channels[chn]->polarity * _channels[chn]->cut * dim_level * global_cut * global_dim * solo_boost;
                         } else {
-                                target_gain = 0.0;
+                                target_gain = GAIN_COEFF_ZERO;
                         }
                 }
 
-                if (target_gain != _channels[chn]->current_gain || target_gain != 1.0f) {
+                if (target_gain != _channels[chn]->current_gain || target_gain != GAIN_COEFF_UNITY) {
 
                         _channels[chn]->current_gain = Amp::apply_gain (*b, _session.nominal_frame_rate(), nframes, _channels[chn]->current_gain, target_gain);
                 }
@@ -380,9 +380,9 @@ void
 MonitorProcessor::set_cut (uint32_t chn, bool yn)
 {
         if (yn) {
-                _channels[chn]->cut = 0.0f;
+                _channels[chn]->cut = GAIN_COEFF_ZERO;
         } else {
-                _channels[chn]->cut = 1.0f;
+                _channels[chn]->cut = GAIN_COEFF_UNITY;
         }
 }
 
@@ -443,7 +443,7 @@ MonitorProcessor::inverted (uint32_t chn) const
 bool
 MonitorProcessor::cut (uint32_t chn) const
 {
-        return _channels[chn]->cut == 0.0f;
+        return _channels[chn]->cut == GAIN_COEFF_ZERO;
 }
 
 bool
@@ -507,7 +507,7 @@ MonitorProcessor::channel_solo_control (uint32_t chn) const
 }
 
 MonitorProcessor::ChannelRecord::ChannelRecord (uint32_t chn)
-	: current_gain (1.0)
+	: current_gain (GAIN_COEFF_UNITY)
 	, cut_ptr (new MPControl<gain_t> (1.0, string_compose (_("cut control %1"), chn), PBD::Controllable::GainLike))
 	, dim_ptr (new MPControl<bool> (false, string_compose (_("dim control"), chn), PBD::Controllable::Toggle))
 	, polarity_ptr (new MPControl<gain_t> (1.0, string_compose (_("polarity control"), chn), PBD::Controllable::Toggle, -1, 1))
diff --git a/libs/ardour/mute_master.cc b/libs/ardour/mute_master.cc
index 5734af8a3d..4c23855915 100644
--- a/libs/ardour/mute_master.cc
+++ b/libs/ardour/mute_master.cc
@@ -90,26 +90,26 @@ MuteMaster::mute_gain_at (MutePoint mp) const
 
         if (Config->get_solo_mute_override()) {
                 if (_soloed) {
-                        gain = 1.0;
+                        gain = GAIN_COEFF_UNITY;
                 } else if (muted_by_self_at (mp)) {
-                        gain = 0.0;
+                        gain = GAIN_COEFF_ZERO;
                 } else {
                         if (muted_by_others_at (mp)) {
                                 gain = Config->get_solo_mute_gain ();
                         } else {
-                                gain = 1.0;
+                                gain = GAIN_COEFF_UNITY;
                         }
                 }
         } else {
                 if (muted_by_self_at (mp)) {
-                        gain = 0.0;
+                        gain = GAIN_COEFF_ZERO;
                 } else if (_soloed) {
-                        gain = 1.0;
+                        gain = GAIN_COEFF_UNITY;
                 } else {
                         if (muted_by_others_at (mp)) {
                                 gain = Config->get_solo_mute_gain ();
                         } else {
-                                gain = 1.0;
+                                gain = GAIN_COEFF_UNITY;
                         }
                 }
         }
diff --git a/libs/ardour/panner_shell.cc b/libs/ardour/panner_shell.cc
index 7b19977b9c..fd5564bbef 100644
--- a/libs/ardour/panner_shell.cc
+++ b/libs/ardour/panner_shell.cc
@@ -284,13 +284,13 @@ PannerShell::distribute_no_automation (BufferSet& inbufs, BufferSet& outbufs, pf
 
 		AudioBuffer& dst = outbufs.get_audio(0);
 
-		if (gain_coeff == 0.0f) {
+		if (gain_coeff == GAIN_COEFF_ZERO) {
 
 			/* gain was zero, so make it silent */
 
 			dst.silence (nframes);
 
-		} else if (gain_coeff == 1.0f){
+		} else if (gain_coeff == GAIN_COEFF_UNITY){
 
 			/* mix all input buffers into the output */
 
@@ -386,7 +386,7 @@ PannerShell::run (BufferSet& inbufs, BufferSet& outbufs, framepos_t start_frame,
 	if (!(as & Play || ((as & Touch) && !_panner->touching()))) {
 
 		// Speed quietning
-		gain_t gain_coeff = 1.0;
+		gain_t gain_coeff = GAIN_COEFF_UNITY;
 
 		if (fabsf(_session.transport_speed()) > 1.5f && Config->get_quieten_at_speed ()) {
 			gain_coeff = speed_quietning;
diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index e22acd8d4d..c2a7c62f6d 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -3457,9 +3457,9 @@ Route::SoloControllable::get_value () const
 	}
 
 	if (Config->get_solo_control_is_listen_control()) {
-		return r->listening_via_monitor() ? 1.0f : 0.0f;
+		return r->listening_via_monitor() ? GAIN_COEFF_UNITY : GAIN_COEFF_ZERO;
 	} else {
-		return r->self_soloed() ? 1.0f : 0.0f;
+		return r->self_soloed() ? GAIN_COEFF_UNITY : GAIN_COEFF_ZERO;
 	}
 }
 
@@ -3521,7 +3521,7 @@ Route::MuteControllable::get_value () const
 
 	// Not playing back automation, get the actual route mute value
 	boost::shared_ptr<Route> r = _route.lock ();
-	return (r && r->muted()) ? 1.0 : 0.0;
+	return (r && r->muted()) ? GAIN_COEFF_UNITY : GAIN_COEFF_ZERO;
 }
 
 void
diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index 31f2635ac3..b69b0bce61 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -2775,7 +2775,7 @@ Session::globally_set_send_gains_to_zero (boost::shared_ptr<Route> dest)
 
 	for (RouteList::iterator i = r->begin(); i != r->end(); ++i) {
 		if ((s = (*i)->internal_send_for (dest)) != 0) {
-			s->amp()->gain_control()->set_value (0.0);
+			s->amp()->gain_control()->set_value (GAIN_COEFF_ZERO);
 		}
 	}
 }
@@ -2788,7 +2788,7 @@ Session::globally_set_send_gains_to_unity (boost::shared_ptr<Route> dest)
 
 	for (RouteList::iterator i = r->begin(); i != r->end(); ++i) {
 		if ((s = (*i)->internal_send_for (dest)) != 0) {
-			s->amp()->gain_control()->set_value (1.0);
+			s->amp()->gain_control()->set_value (GAIN_COEFF_UNITY);
 		}
 	}
 }