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

1 files changed, 11 insertions, 11 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);