Fix rounding errors in pitch calculation

Fixes #317

Author: Bentroen

scripts/mp3_export/mp3_export.gml

@@ -36,10 +36,11 @@ function mp3_export() {
 	                var key = song_key[a, b];
 	                var vel = song_vel[a, b]; 
 					var pit = song_pit[a, b];
+					var keyshift = key + (ins.key + (pit/100) - 78)
 	                if (ins.loaded) {
 	                    err = audio_sound_add(ins.file_id,
 	                                          a / tempo,
-	                                          0.5 * power(1.06, (key + (ins.key + (pit/100) - 78 - 0.23))),
+	                                          0.5 * power(2, keyshift / 12),
 	                                          layervol[b] / 100 / 100 * vel)
 	                    if (err < 0) {
 	                        if (language != 1) message("There was an error when saving as MP3.\nError code: c" + string(err), "Error")

scripts/play_sound/play_sound.gml

@@ -7,7 +7,7 @@
 /// @param  fine pitch
 function play_sound(argument0, argument1, argument2, argument3, argument4) {
 
-	var ins, key, vol, pan, newemitter, emitter, pit
+	var ins, key, vol, pan, newemitter, emitter, pit, keyshift
 	ins = argument0
 	key = argument1
 	vol = argument2
@@ -17,7 +17,8 @@ function play_sound(argument0, argument1, argument2, argument3, argument4) {
 	if (!ins.loaded)
 	    return 0
 	emitter=audio_emitter_create()
-	audio_emitter_pitch(emitter, 0.495 * power(1.06, (key + (ins.key + (pit/100) - 78))))
+	keyshift = key + (ins.key + (pit/100) - 78)
+	audio_emitter_pitch(emitter, 0.5 * power(2, keyshift / 12))
 	audio_emitter_gain(emitter, (vol / 100) * mastervol)
 	if (realstereo = 0) audio_emitter_position(emitter,pan,0,0)
 	else audio_emitter_position(emitter,100,0,0)