Ports a rewritten version of BAYSTRUMENTS (#11680)

* bay instruments

* k

* AAA

* remove that

* changes

* Update _instrument_key.dm

* safety nets

* @ghommie fixed

* volume

* Update item.dm

* Update item.dm

Co-authored-by: Ghom <42542238+Ghommie@users.noreply.github.com>

code/modules/instruments/instrument_data/_instrument_key.dm

@@ -0,0 +1,20 @@
+/datum/instrument_key
+	var/key			//1 to 127
+	var/sample		//file
+	var/frequency	//frequency generated
+	var/deviation	//deviation up/down towards pivot from sample (??)
+
+/datum/instrument_key/New(sample = src.sample, key = src.key, deviation = src.deviation, frequency = src.frequency)
+	src.sample = sample
+	src.key = key
+	src.deviation = deviation
+	src.frequency = frequency
+	if(!frequency && deviation)
+		calculate()
+
+/datum/instrument_key/proc/calculate()
+	if(!deviation)
+		CRASH("Invalid calculate call: No deviation or sample in instrument_key")
+	#define KEY_TWELTH (1/12)
+	frequency = 2 ** (KEY_TWELTH * deviation)
+	#undef KEY_TWELTH