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PostPosted: 2019-05-31, 22:20:50 
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Which FM chip has the most operators?

When we talk about FM synth chips, it's my understanding that there is a fixed pool of operators that can be reconfigured in various ways. i.e., the YMF262 has 36 operators that can be configured in various 2-op and 4-op modes.
Are there any chips that support 6-operator algorithms? Like something that could even play DX7 patches.

I suppose everyone turned to PCM before FM chips got too powerful...

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PostPosted: 2019-06-01, 0:10:42 

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The SCSP chip in the Sega Saturn would probably be it. It has 32 PCM channels, and each can be configured to modulate another. Essentially meaning that you can get any kind of FM modulation, 6op like the DX7 (or even more operators if you feel like it), plus arbitrary waveforms like the OPL series. Just keep in mind that polyphony decreases for each FM voice you use.

There's also a built in DSP for all kinds of sound effects including filtering, reverb and what not.

The AICA chip in the Dreamcast is based on the SCSP but has twice as many channels. Not 100% sure if it supports FM though.


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PostPosted: 2019-06-01, 1:52:00 
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Interesting! I don't see Saturn in the vgmrips list of systems. I see this is also known as YMF292.
Is this chip something we'll ever see in vgmplay?

Cool sound, can barely tell what's FM and what's PCM.
https://www.youtube.com/watch?v=y9VXL3Z ... 2T&index=5

wow -
https://www.youtube.com/watch?v=CI48WET ... T&index=12

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PostPosted: 2019-06-01, 9:25:54 

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I don't think we'll see SCSP stuff anytime soon.

So far I've only made a few test rips.
Unfortunately they suffer from bad timing, which is especially noticeable in Fighting Vipers. So I decided to disable SCSP logging in the MAME VGM mod.
Aside from that, SCSP stuff from Sega Model 2 is really hard to trim due to dynamic channel allocation.

I probably should at least replace the SCSP emulation in VGMPlay with a good one though. The MAME core doesn't support FM at all.


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PostPosted: 2019-06-01, 10:39:21 

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Because Sega went for a modular design with the SCSP, I'm not sure if we even need VGM logging. The chip was always paired with a 68000 sound CPU, and the peripheral hardware isn't too different between the Saturn hardware and Model 2/3 boards; the arcade boards have lots of ROM for samples but they are still constantly swapped into RAM whenever used, similar to Mega CD and System 18 hardware. So the SSF format is probably sufficient for Saturn music, I think.


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PostPosted: 2019-06-15, 1:13:00 

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mmontag wrote:
When we talk about FM synth chips, it's my understanding that there is a fixed pool of operators that can be reconfigured in various ways. i.e., the YMF262 has 36 operators that can be configured in various 2-op and 4-op modes.

Actually there’s only one operator which is used 36 times per sample :). But I guess that’s a technicality :).

Other than that I think 6 operators is really not as great as it seems, as the number of modulators put in series increases it becomes very hard to do sensible sound design. More than 4 is rarely used I think, most of the 6-op patches have at least two carriers and can thus also be played with a 4-op or 2-op FM chip by combining channels. Such channel layering is not very practical for a performance instrument, so that’s why 6-op is better for the DX7. But for chips 4-op is just fine.

Because you can’t control the frequency of the operators independently, but rather specify a frequency per channel, the 2-op and 4-op gives you more flexibility than a 6-op chip would, which binds 6 operators to a single channel. You can assign and use the operators more efficiently on the 2-op and 4-op variants. Had the OPNA been 6-op, it would’ve had only 4 channels rather than 6, definitely a bad trade-off.

The bigger problem with the YMF262 OPL3 is not that it’s got “only” 4 operators, but that the selection of four 4-op algorithms (configurations) is small and also not great, when compared to the OPM / OPN series which were natively 4-op and offered 8 much more varied algorithms. The strength of the OPL3 on the other hand is the massive amount of channels, and the ability to select 7 more waveforms in addition to sines, giving it a whole different dimension of sound design.


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PostPosted: 2019-06-16, 8:31:15 
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Hm. That's pretty insightful. Shouldn't discount the little FM chips.

What I'm wishing for, I guess, is a synthesis engine that does more *without resorting to audio samples*. For example, imagine if there was a console that shipped with a subtractive synth on chip.

The thing that comes closest is perhaps Farbrausch V2:
https://www.youtube.com/watch?v=gb6EO7L0EuQ

It's a masterpiece of efficiency :)

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