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Chris
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YM2612 Questions
Post Posted: Wed Jun 30, 1999 8:01 pm
This message especially goes out to Paul Jenson. How many channels are used in that
processor? How many instruments are used in it? What are some of it's precussion
features? Even though the YM2413 is an older model than the YM2612, are there
any fast improvements between the two? Like, I know the YM2612 uses less sound
channels than the YMxxxx used in System 18 games like Altered Beast and Golden
Axe. The reason why I ask is because someday I would like to write a Genesis
emulator for MSDOS and I would like to play the sound via Adlib FM sound. The
Adlib uses 9 sound channels and I think up to 3 can be used to play precussion
sounds. I have an excellent document on the YM2413 and they have similar
as the Adlib FM processor used in the PC.

Chris :o)
 
  • Joined: 29 Jun 1999
  • Posts: 254
  • Location: California, USA; Hiroshima, Japan
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Post Posted: Thu Jul 01, 1999 12:21 am
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> This message especially goes out to Paul Jenson. How many channels are used in that processor?

The YM2612 has 6 FM channels, and a digital audio channel (DAC). FM ch6 is turned off if the DAC is enabled, but you can still write to ch6 to change the speaker position of the DAC (left/right/both). Also ch3 can be set to a special mode that allows the four operators that make up a particular instrument to be set at seperate frequencies, and enabled individually. This special mode is most often used for synth drum effects (like the bongos in Bare Knuckle/Streets of Rage) and FM sound effects.

How many instruments are used in it?

As many as you like. If I understand correctly, each FM channel is made up of 4 preset waveforms, which are modified by changing the registers for attack rate (AR), primary decay (DR1), release rate (RR), and secondary decay (DR2). The 2612 has 8 selectable feedback algorithms that determine how the modified waveforms (called operators) feed into one another.

Since the 2612 uses no preset instruments, and since nearly everything can be modified on the fly, you can make almost any type of (FM) sound you want. The bitchy thing about this is that there is no easy way to tell exactly what type of instrument is trying to be synthesized.

What are some of it's precussion
Quote
> features?

Like I said earlier, percussion sounds can be generated using FM ch3 in special mode, but most newer games use the DAC for drums. It doesn't have any built-in percussion sounds, so all sounds must be created by using the registers.

Some games use the PSG to simulate drums. Good examples of this are Assault Suits Leynos (Target Earth), and Super Hydlide.

Even though the YM2413 is an older model than the YM2612, are there
Quote
> any fast improvements between the two?

Well, from looking at the 2413 data sheet, it seems to be a much simpler chip. The 2413 uses 15 preset instruments, and can use either 9 simultaneous FM channels w/out percusion, or 6 simultaneous FM channels w/ 5 percussion channels. Also, one of the FM channels is user-defined, so it can be used for sound effects.

The 2413 is easier to program, but a grater variety of sounds can be generated with the 2612. Also, the 2612 has a DAC.

Like, I know the YM2612 uses less sound
Quote
> channels than the YMxxxx used in System 18 games like Altered Beast and Golden
> Axe. The reason why I ask is because someday I would like to write a Genesis
> emulator for MSDOS and I would like to play the sound via Adlib FM sound. The
> Adlib uses 9 sound channels and I think up to 3 can be used to play precussion
> sounds. I have an excellent document on the YM2413 and they have similar
> as the Adlib FM processor used in the PC.

Even though I know next to nothing about sound card programming (that is, digital FM emulation), I don't think it should be that difficult. The hardest thing would probably be to emulate the percussion channels, and fit 5 of them into 3 AdLib channels.

Hope this helps,

Paul
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Chris
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Thanks
Post Posted: Thu Jul 01, 1999 3:47 am
Man, you really know a lot about these Yamaha frequency chips. Besides writing GYM2MID,
have you actually done programming with these chips?

Chris :o)
 
Limbs a Flyin'
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Post Posted: Thu Jul 01, 1999 8:19 am

Quote
> This message especially goes out to Paul Jenson. How many channels are used in that
> processor? How many instruments are used in it? What are some of it's precussion
> features? Even though the YM2413 is an older model than the YM2612, are there
> any fast improvements between the two?
2413 (clone of 3812 - adlib chip, so thats what i will refer to) keeps its 5 percussion sounds in its own little sample rom.
apparently stored at 11025hz, 8bit mono, they are:
snare
hihat
tom
bass
top cymbal
(note that its a drum kit, so not all sounds are drums - sensible, eh?)
the opl chip found in sb16 and a bit earlyer is 3812 compatible, but i think it makes its drum kit noise via fm, rather than samples (sounds a bit poor), and the opl3 chip in the sb16 is stereo - basicly one 3812 compatible on each speaker. my sb16 manual claimed either 2 or 4 operator support, but i think their definition of 4 operator is to have 2 on one speaker per channel, 2 on the other (not related to the 'real' 4 operator per channel that the 2612 and its relatives have)

Quote
> Like, I know the YM2612 uses less sound
> channels than the YMxxxx used in System 18 games like Altered Beast and Golden
> Axe. The reason why I ask is because someday I would like to write a Genesis
> emulator for MSDOS and I would like to play the sound via Adlib FM sound. The

try checking out version 0.20 of Genecyst (http://zophar.net/genecyst/gcyst020.zip ) to see that in action.. its not a very faithfull reproduction, due to the 2612 having 4 operators per channel, where as the adlib (3812 + clones) have 2 ops per channel..

Quote
> Adlib uses 9 sound channels and I think up to 3 can be used to play precussion
> sounds. I have an excellent document on the YM2413 and they have similar
> as the Adlib FM processor used in the PC.

> Chris :o)

adlib is 2 ops per channel - sounds a bit poor.
2612 4 ops per channel sounds better - can make some funky sounds - not limited to just 'normal' musical instruments.
i wonder what 6,8,or 10 op fm would be like..

to sum it up, 2612 and 2413 are related due to the fact that they are fm chips, but not close enough to make each chip sound like each other. (well, a 2612 may be able to sound like a 2413 - perhaps you could write a genny emu which also supports sms, and runs the 2413 sms fm through the 2612 fm engine?!)
 
Alex'99
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Post Posted: Thu Jul 01, 1999 12:47 pm
.....................

Quote
> to sum it up, 2612 and 2413 are related due to the fact that they are fm chips, but not close enough to make each chip sound like each other. (well, a 2612 may be able to sound like a 2413 - perhaps you could write a genny emu which also supports sms, and runs the 2413 sms fm through the 2612 fm engine?!)

Yeah! a Emulator of YM2413 for my Sega16bits with YM2612.

Is very GOOD_IDEA ;)


Alex'99
 
  • Joined: 29 Jun 1999
  • Posts: 254
  • Location: California, USA; Hiroshima, Japan
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No programming whatsoever. *nt*
Post Posted: Thu Jul 01, 1999 5:38 pm
Quote
> Man, you really know a lot about these Yamaha frequency chips. Besides writing GYM2MID,
> have you actually done programming with these chips?

> Chris :o)
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Richard Mitton
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Post Posted: Thu Jul 01, 1999 8:48 pm
The YM2612 and YM2413 aren't really related too much at all.
They both use the same FM system, but the YM2413 had 9 channels, which could only be set to pre-defined instruments.
(I think it could have 1 custom instrument).

The YM2612 has 6 channels, each with 4 operators (compared to the YM2413, which has 2 operators per channel).
It also has a Digital-Analogue Convertor, but *doesn't* have any percussion features.

The chip used by the System 18 is *almost* exactly the same as the YM2612 (same number of channels).

In order to emulate the YM2612 via an Adlib, you need to use the OPL3 extensions. You have to put the Adlib into 4-operator mode.
It will basically work if you re-scale all the values to fit, the main problem is converting the different connection algorithms. (The Adlib doesn't have as many)

Hope that helps a bit.
 
Limbs a Flyin'
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Post Posted: Fri Jul 02, 1999 7:30 am

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> In order to emulate the YM2612 via an Adlib, you need to use the OPL3 extensions. You have to put the Adlib into 4-operator mode.

so the opl3 chip does have a real 4 op support? does anyone know of any further info about this (assuming its true, of course ;)
 
Richard Mitton
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Post Posted: Fri Jul 02, 1999 11:44 pm

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> so the opl3 chip does have a real 4 op support? does anyone know of any further info about this (assuming its true, of course ;)

Yes, it does. I can confirm it. I've written a YM2612 emulator for it (!)

(sorry, not for public release yet)
 
MasterDragon
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Post Posted: Sat Jul 03, 1999 12:24 pm

Quote
>
> > In order to emulate the YM2612 via an Adlib, you need to use the OPL3 extensions. You have to put the Adlib into 4-operator mode.

> so the opl3 chip does have a real 4 op support? does anyone know of any further info about this (assuming its true, of course ;)

Yeah. There's a register in the OPL3 than can be used to combine certain pairs of 2-operator channels into 4-operator channels.
 
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