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ÿ               Written by Arnaud Carre. (leonard@mygale.org)               ڴ



	NEW: "YM3b" Format !!! See bellow...

	WARNING: YM4! format is changed !!!


	Many people asked me how to find new YM files. Well, the problem is
that it takes me too much time to convert new modules. Then I decide to give
you my YM-File format, so you can generate YM-File by yourself !



	As you probably know, YM is only an YM2149 Chip emulator, not a true
MC68000 emulator. (For the moment !). YM-Files does not contain any 68000
code routine. A music-file is composed of YM2149 registers generated by the
original play-routine for each 50th seconds. As the YM2149 has 14 registers
8 bits each, that means 14 bytes for 1/50 second, so 700 bytes for one
second of soundchip.

	When I convert an ATARI music, I play the music on the ATARI, and I
store YM2149 registers set each 1/50sec (Vertical Blank time, VBL) in a big
file as follow:

	VBL1:
		store reg0,reg1,reg2,...,reg12,reg13	(14 regs)
	VBL2:
		store reg0,reg1,reg2,...,reg12,reg13	(14 regs)


				..........


	VBLn:
		store reg0,reg1,reg2,...,reg12,reg13	(14 regs)


	The problem is that is takes a lot of disk-space. Just count: A 10
minutes song will take 420000 bytes on disk. But don't panic, the music are
compressed with LHARC method (using LHA program from Haruyasu Yoshizaki).
To reach best compression ratio, I store registers in a different order:


	VBL1 reg0, VBL2 reg0, VBL3 reg0 .... VBLn reg0

	VBL1 reg1, VBL2 reg1, VBL3 reg1 .... VBLn reg1


				..........


	VBL1 reg14,VBL2 reg14,VBL3 reg14.... VBLn reg14



        So, here is the old YM3 file format:


	Offset	Size	Name	Value   Comments
	0	4	ID	'YM3!'	File type Identificator.

	then YM2149 registers starts a offset 4.

	The number of used VBL for music can be computed as follow:

	nvbl = (ymfile_size-4)/14;


------------------------------------------------------------------------------
WARNING:
	The LHA compression must be called AFTER the file is generated. ALWAYS
	USE THE HEADER TYPE 0 when compressing (-h0).
	Ex: You just create your binary file, starting with 'YM3!' ID, then
	all YM registers. The music is 2 minutes long, that means your
	binary is 2*60*700 + 4 = 84004 bytes long. you must compress it before
	using the file with YM.EXE: (ex: your binary is TEST.BIN)

	LHA a -h0 TEST.LHA TEST.BIN

	Then a file TEST.LHA is created, wich is DIRECTLY a valid YM file.
	just type:

	ren test.lha test.ym

	Then you can hear the file with YM.EXE

        (I use LHA.EXE v2.13).
------------------------------------------------------------------------------


------------------------------------------------------------------------------
WARNING:
	Some old and specific music starts with header 'YM2!', don't use this
	ID.
------------------------------------------------------------------------------






SPECIAL: Register 13 !
----------------------

	Creating a binary with YM registers for each VBL is easy. However
there is special case concerning register 13. Reg13 is used for the volume
envelope wave-form on the YM2149. The problem is writing to that register
"restarts" the wave-form at beginning. That is, you CAN'T access this regis-
ter each VBL if the original play-routine does not. So, if the original
player does not write to register 13 on VBL n, write 0xff value.
(So when YM.EXE read 0xff as reg13, the internal emulator register is not
updated).


That's all for 'YM3!' file.
---------------------------

	That's all for the 'YM3!' format. As you see, it is very simple (then
not very powerfull) but you can convert many atari soundchip tunes with that
format. (Especially old game-music, wich use very simple play-routine, or
AMSTRAD CPC music).

	But if you know the ATARI demos, you probably know there is many
tricks used by sound-player to produce real-drums or distorted sound: sample
for drums, additional tone synthesis using TIMER etc... The 'YM3!' format can
not play such music so...




NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW
---------------------------------------------------------------------------

	These days you can find many YM tunes on Internet World Wide Web. Many
of these are generated with automatic program. (See the ATARI program written
by Jochen Knaus). The problem is that for each music, the generating program
must know the music time. (And even the loop position if it exists !). So I
write a PC program (YMTOOL.EXE) wich:
	-Read an YM file.
	-Display infos about it.
	-Search loop automaticly in the music.
	-Save a new YM file with fine loop.

The new YM file supports the loop point to be at the middle of a music (not
only at the beginning, as the YM3 format). So a new format is born: "YM3b".
The only difference is "YM3b" instead of "YM3!" and the music file contains
one DWORD (32bits integers) at the end of the file, wich contains the frame
number at wich the loop restart.
Ex: If a music is 5600 frames and the loop restarts at frame 432, just write
"YM3b", then 5600*14 bytes of YM registers, then 432.

Go to my web-page to habe link to download YMTOOL.EXE or to find link to
Jochen Knaus homepage:

www.mygale.org/09/leonard/



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ÿ                                                                           ڴ



	The 'YM4!' format is not currently implemented in the YM emulator, but
I have written the most complete format to play all "evoluated" music such as
SCAVENGER or ETERNAL tunes. If you convert a music wich the player does not use
any "hardware" trick such digi-drum or synth-tune, use 'YM3!' format describe
above: it will be faster and easyer to create. (Almost all standart YM file
existing around the world (exept DIGI-Drums ones) can be written in YM3
format).

	If you want to convert a SPECIAL music wich use many tricks to produce
strange sound, you must be familiar with ATARI-ST sound programing and follow
next instructions...




Additional sound effects used by strange-player are only two types differents:



1) Digi-Drums
--------------


	Generally digi-drums is a bunch of sample in the orignal play-rout.
You will have to localize and extract them. In the YM file, you have to
store the sample with their respective size. (see next part)
        when playing, a digi-drum is defined with one value: timer frequency
to replay sample.



2) Tone synthesis
-----------------


	To produce very funny sound, some player use the ATARI-ST timer
controller to change YM2149 volume more than 1 time per VBL. Generally
the routine in the player is as follow:

lab1:	move.l	#$08000f00,$ffff8800.w
	move.l	#lab2,$134.w
	rte

lab2:	move.l	#$08000000,$ffff8800.w
	move.l	#lab1,$134.w
	rte

	So the volume is set to 15 then to 0 then to 15 etc... many times
in the same VBL at a given frequency. In fact, the volume switch always
between 0 and vmax. So a tone-synthesis is define by two values: vmax and
timer frequency.



3) 'YM4!' File format:
----------------------


	Here is the description of the binary YM4 file. After the file is
created, you can compress it with LHA -h0 as above.


	Legend:	BYTE		8bits integer.
		WORD 		16bits integer.
		DWORD		32bits integer.
		string[n]	Ascci string of n bytes long.
		NT-String	NULL-Terminated string.


        WARNING: All DWORD or WORD are stored in MOTOROLA order in the file
		 (INTEL reverse)



	Offset	Size	Type		Comment
	0	4	DWORD		ID of YM4 format. ('YM4!')
	4	8	string[8]	Check String ('LeOnArD!')
	12	4	DWORD		Nb of valid VBL of the file.
	16	4	DWORD		Song attributes (see bellow)
	20	4	DWORD		Nb of digi-drum sample (can be 0)
	24	4	DWORD		Frame loop start (generally 0)

	For each digidrum sample:
	{
	..	4	DWORD		sample size
        ..      ?       BYTES           sample data (8bits per sample)
	}

	..	?	NT-String	Name of the song.
	..	?	NT-String	Name of the author.
	..	?	NT-String	Comments (Name of the YM converter !)
	..	?			All YM2149 registers.
	..	4	DWORD		End-File check. ('End!')




	So you've seen in the YM3 format that all 14 registers of the YM2149
are saved in file each VBL. Now, I had to add 2 "virtual" registers to store
extended information. So there is 16 bytes in the file for each VBL. Now the
VBL number n will be noticed "Vn" and register m "Rm". First VBL is V0 and
first register is R0. (R0 to R15)

	The file data block will be composed of:

	V0R0,V0R1,V0R2,....,V0R14,V0R15
	V1R0,V1R1,V1R2,....,V1R14,V1R15
	.....
        This is the non-interleaved format block.



	The data block can be on a different form:

	V0R0,V1R0,V2R0,....,VnR0
	V0R1,V1R1,V2R1,....,VnR1
	....
	V0R15,V1R15,V2R15,....,VnR15

	This is the interleaved format block.

	Those who are reading till now have noticed that the YM3 format is
an interleaved format. In fact, the YM4 format can be interleaved or not.
(Interleaved format offers a very powerfull compression ratio when compressed
with LHA).



	Let's see the DWORD "song attribute":
	(bn represent the bit n of the DWORD)

	b0:	Set if Interleaved data block.
	b1:	Set if the digi-drum samples are signed data.
	b2:	Set if the digidrum is already in ST 4 bits format.

        b3-b31: Not used yet, MUST BE 0.

	Here come valid bits for standard 14 first registers:
	(Same as YM3 Format.)
	(- means Unused, X means used)

	NOTE: Now, digi-drum will be noticed DD and Timer-Synth will be
	      noticed TS.



		b7 b6 b5 b4 b3 b2 b1 b0
	r0: 	 X  X  X  X  X  X  X  X		Period voice A
	r1:	 -  -  -  -  X  X  X  X		  "      "   "
	r2: 	 X  X  X  X  X  X  X  X		Period voice B
	r3:	 -  -  -  -  X  X  X  X		  "      "   "
	r4: 	 X  X  X  X  X  X  X  X		Period voice C
	r5:	 -  -  -  -  X  X  X  X		  "      "   "
	r6:	 -  -  -  X  X  X  X  X		Noise period
	r7: 	 X  X  X  X  X  X  X  X		Mixer control
	r8:	 -  -  -  X  X  X  X  X		Volume voice A
	r9:	 -  -  -  X  X  X  X  X		Volume voice B
	r10:	 -  -  -  X  X  X  X  X		Volume voice C
	r11:	 X  X  X  X  X  X  X  X		Waveform period.
	r12:	 X  X  X  X  X  X  X  X		   "       "
	r13:	 -  -  -  -  X  X  X  X		Waveform shape.

	New "virtual" registers to store extra data:

	r14:     -  -  -  -  -  -  -  -		Frequency for DD1 or TS1.
	r15:     -  -  -  -  -  -  -  -		Frequency for DD2 or TS2.


	As we've seen, r13 has a particular status. If the value stored in
the file is 0xff, YM emulator will not reset the waveform position.

	The YM4 format provides to start or run 1 TS and 1 DD during the
same VBL.


	You notice there is a least 28 free bits in the 14 standard
registers. YM4 format use them to store "extra" information. Let's see
the "extra" bits:




	r1 free bits are used to code TS:
	r1 bits b5-b4 is a 2bits code wich means:

	00:	No TS.
	01:	TS running on voice A
	10:	TS running on voice B
	11:     TS running on voice C

	r1 bit b6 is only used if there is a TS running. If b6 is set, YM
emulator must restart the TIMER to first position. (You must be VERY sound-
chip specialist to hear the difference).

	r3 free bits are used to code a DD start.
	r3 b5-b4 is a 2bits code wich means:

	00:	No DD
	01:	DD starts on voice A
	10:	DD starts on voice B
	11:	DD starts on voice C


WARNING:If a DD starts on voice V , the volume register corresponding to V
(Ex r8 for voice A, r9 for B and r10 for C) contains the sample number in
5 low bits. (That mean you have 32 digiDrum max in a song)



	Concerning DD and TS, both effects need to be played at a given
frequency. On the ATARI-ST, play routine use the MFP-TIMER chip. That is,
any frequency can be coded on 13bits: 8bits for timer count, and 3bits
for timer predivisor. The MFP runs at 2457600 Hz and has a preset of
predivisor:

	000:	Timer stop.
	001:	Prediv by 4
	010:	Prediv by 10
	011:    Prediv by 16
	100:    Prediv by 50
	101:    Prediv by 64
	110:    Prediv by 100
	111:    Prediv by 200

	The 8 bits timer count value is named TC and 3bits prediv value
	is named TP.

	Some ex to endserstand how it works:

	TP	TC	Frequency (Hz)
	1	28	(2457600/4)/28   = 21942 Hz
	4	150	(2457600/50)/150 = 327 Hz



Encode:
-------
	TP for TS is stored in the 3 free bits of r6 (b7-b5)
	TP for DD is stored in the 3 free bits of r8 (b7-b5)
	TC for TS is stored in the 8 bits of r14
	TC for DD is stored in the 8 bits of r15

	4bits volume value (vmax) for TS is stored in the 4 free bits of r5
(b7-b4)





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	Well, it seems that BEFORE I acheive the YM4 format loading rout, some
of you (particulary Mage!) ask me to change a bit the format to add extra
information. So here is YM5 format: (the YM4 is obsolete now)


	Offset	Size	Type		Comment
	0	4	DWORD		ID of YM5 format. ('YM5!')
	4	8	string[8]	Check String ('LeOnArD!')
	12	4	DWORD		Nb of valid VBL of the file.
	16	4	DWORD		Song attributes (see bellow)
	20	2	WORD		Nb of digi-drum sample (can be 0)
	22	4	DWORD		YM2149 External frequency in Hz
					(ex:2000000 for ATARI-ST version,
					    1000000 for AMSTRAD CPC)
	26	2	WORD		Player frequency in Hz
					(Ex: 50Hz for almost player)
	28	4	DWORD		Vbl number to loop the song.
					(0 is default)
	32	2	WORD		Size (in bytes) of futur
					additinal data.
					(must be 0 for the moment)

	For each digidrum sample:
	{
	..	4	DWORD		sample size
        ..      ?       BYTES           sample data (8bits per sample)
	}

	..	?	NT-String	Name of the song.
	..	?	NT-String	Name of the author.
	..	?	NT-String	Comments (YM file converter ?!)
	..	?			All YM2149 registers.
	..	4	DWORD		End-File check. ('End!')


	Ok, YM4 Expert had notice there is no major change.





4) Pfff....
-----------

        That's all for the YM4 format wich allow you to encode most
of the demo-soundchip from the ATARI. If some of you think the file format is
a bit hard to assume I agree with you. I only prefer a complex but shorter
format than simple and big one...

	If you have any trouble, problem or questions about YM3 or YM4 format,
write or mail me:

Internet E-Mail:
        leonard@mygale.org

WEB Page:
	www.mygale.org/leonard/09/

French "Minitel"
	3615 RTEL bal "LEONHARD" (with a H)


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				Have a nice day !

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