diff --git a/games/keen/SFX b/games/keen/SFX
index da82300a..17cfab8f 100644
--- a/games/keen/SFX
+++ b/games/keen/SFX
@@ -6,8 +6,8 @@ Based on dumped code by the "KeenFX" tool
 	Note: 65535-value = note freq
 
 3) WLDENTERSND
-	64155, 10
-	63495, 5
+	64155, 10	; 1380Hz F6?
+	63495, 5	; 
 	0,16
 	62355,2
 	62175,16
diff --git a/games/keen/speaker_tone.s b/games/keen/speaker_tone.s
index 069cf498..1d304fac 100644
--- a/games/keen/speaker_tone.s
+++ b/games/keen/speaker_tone.s
@@ -1,21 +1,40 @@
-; based on code from here
+; this code was widely shared for playing tones on Apple II
+;	by POKEing the machine language and CALLing from BASIC
+
+; it's originally by Paul Lutus, from the Apple II Red Book p45
+
+
+; it's hard to find good info on this, but loading from $C030
+;	"toggles" the speaker.  So toggling twice is esentially a square wave?
+
+; using regular load/store/bit of $C030 is safe.  Some of the more
+;	advanced addressing modes can double-toggle due to how some 6502
+;	implementations run the address bus
+
+; these seem to have been calculated assuming a 1MHz clock
+;	but the Apple II actually runs at roughly 1.023MHz
+
+; or a frequency of 1/(speaker_freq*20.46e-6)
+
+; to go other way, speaker_freq=1/(freq*20.46e-6)
+
+; this table of notes was from
 ; http://eightbitsoundandfury.ld8.org/programming.html
+; but seems off a bit and also assumes 1MHz clock
 
-; A,X,Y trashed
-; duration also trashed
-
-NOTE_C3		=	255
-NOTE_CSHARP3	=	241
-NOTE_D3		=	227
-NOTE_DSHARP3	=	214
-NOTE_E3		=	202
-NOTE_F3		=	191
-NOTE_FSHARP3	=	180
-NOTE_G3		=	170
-NOTE_GSHARP3	=	161
-NOTE_A3		=	152
-NOTE_ASHARP3	=	143
-NOTE_B3		=	135
+;				1MHz			1.023MHz
+NOTE_C3		= 255	; G3=5217us = 192Hz (G3,  5218us = 196Hz	249)
+NOTE_CSHARP3	= 241	; 4931us = 203Hz (G#3, 4931us = 207Hz
+NOTE_D3		= 227	; 
+NOTE_DSHARP3	= 214
+NOTE_E3		= 202
+NOTE_F3		= 191
+NOTE_FSHARP3	= 180
+NOTE_G3		= 170
+NOTE_GSHARP3	= 161
+NOTE_A3		= 152
+NOTE_ASHARP3	= 143
+NOTE_B3		= 135	; 1350us = 740Hz (F#5)
 
 NOTE_C4		=	128
 NOTE_CSHARP4	=	121
@@ -43,20 +62,38 @@ NOTE_A5		=	38
 NOTE_ASHARP5	=	36
 NOTE_B5		=	34
 
+; B5 = 988 Hz, 1021us
 
 
+;=====================================================
+; speaker tone
+;=====================================================
+; A,X,Y trashed
+; duration also trashed
+
+; this was designed by basic to be poked into 770 ($302)
+;	on an Applesoft CALL, X=$9d, Y=$02  (A,Y = Address to call)
+; it was originally designed for Integer BASIC where Y=0 on call
+
+	; the inner freq loop is roughly FREQ*10cycles
+	; so the square wave generated has a period of
+	;	freq*20*1.023us
+	; or a frequency of 1/(freq*20.46e-6)
+
 speaker_tone:
-	lda	$C030		; click speaker
+	ldy	#0							; 3
+speaker_tone_loop:
+	lda	$C030		; click speaker				; 4
 speaker_loop:
-	dey			; y never set?
-	bne	slabel1		; duration roughly 256*?
-	dec	speaker_duration	; (Duration)
-	beq	done_tone
-slabel1:
-	dex
-	bne	speaker_loop
-	ldx	speaker_frequency	; (Frequency)
-	jmp	speaker_tone
+	dey			;					; 2
+	bne	freq_loop	;					; 2/3
+	dec	speaker_duration	; (Duration)			; 6
+	beq	done_tone						; 2/3
+freq_loop:
+	dex								; 2
+	bne	speaker_loop						; 2/3
+	ldx	speaker_frequency	; (Frequency)			; 4
+	jmp	speaker_tone_loop					; 3
 done_tone:
 	rts