Make audio bus channels' peak volume consistent

Channels that are inactive -or when playback has not started yet- will report -200 dB as their peak value (which is also the lowest value possible during playback).

(cherry picked from commit a2b3a73e2d0c2b9e9badeab28fef26565a9ec3f2)

core/math/audio_frame.h

@@ -47,6 +47,9 @@ static inline float undenormalise(volatile float f) {
 	return (v.i & 0x7f800000) < 0x08000000 ? 0.0f : f;
 }
 
+static const float AUDIO_PEAK_OFFSET = 0.0000000001f;
+static const float AUDIO_MIN_PEAK_DB = -200.0f; // linear2db(AUDIO_PEAK_OFFSET)
+
 struct AudioFrame {
 
 	//left and right samples

servers/audio_server.cpp

@@ -411,9 +411,10 @@ void AudioServer::_mix_step() {
 		}
 
 		for (int k = 0; k < bus->channels.size(); k++) {
-
-			if (!bus->channels[k].active)
+			if (!bus->channels[k].active) {
+				bus->channels.write[k].peak_volume = AudioFrame(AUDIO_MIN_PEAK_DB, AUDIO_MIN_PEAK_DB);
 				continue;
+			}
 
 			AudioFrame *buf = bus->channels.write[k].buffer.ptrw();
 
@@ -446,7 +447,7 @@ void AudioServer::_mix_step() {
 				}
 			}
 
-			bus->channels.write[k].peak_volume = AudioFrame(Math::linear2db(peak.l + 0.0000000001), Math::linear2db(peak.r + 0.0000000001));
+			bus->channels.write[k].peak_volume = AudioFrame(Math::linear2db(peak.l + AUDIO_PEAK_OFFSET), Math::linear2db(peak.r + AUDIO_PEAK_OFFSET));
 
 			if (!bus->channels[k].used) {
 				//see if any audio is contained, because channel was not used

servers/audio_server.h

@@ -204,7 +204,7 @@ private:
 				last_mix_with_audio = 0;
 				used = false;
 				active = false;
-				peak_volume = AudioFrame(0, 0);
+				peak_volume = AudioFrame(AUDIO_MIN_PEAK_DB, AUDIO_MIN_PEAK_DB);
 			}
 		};