YM2612 / TX81Z Patch Compatibility

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ShannonS
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YM2612 / TX81Z Patch Compatibility

Post by ShannonS » Mon Oct 22, 2012 4:24 am

I've been writing a program to play YM2612 VGM files on my Yamaha TX81Z (based on the YM2414) . I've gotten far enough that I can get songs playing fine and some of them sound quite good but the instruments don't sound quite right.
The register set for the YM2612 seems almost identical to the TX81Z midi parameters with a few exceptions.

The one I am struggling with at the moment is the output level of each operator (similarly the sustain level of the envelopes). The TX81Z uses a 0-99 with 99 being the maximum level. The YM2612 use 0-127 with 0 being being maximum level. I can't come up with a good way of mapping this parameter to get the sounds to match.
I'm pretty sure the YM2414 uses the same 0-127 attenuation as the register value and the cpu in the TX81Z converts it from a more user friendly 0-99.

I can get it to sound reasonably close with with various non-linear mappings but I would prefer to use the actual method if anyone knows it. It should be the same one all the DX series synthesizers use.

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TmEE co.(TM)
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Post by TmEE co.(TM) » Mon Oct 22, 2012 6:23 am

Do you know any decibel relation of the 0 ti 99 mapping ?

1 step in 0.75db on all 0...127 scale, 8 steps is 6db and so on.
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KanedaFr
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Post by KanedaFr » Mon Oct 22, 2012 11:32 am

some years ago, I worked on TX81, FB01 and DX7 patch import (if I remember correctly the names)
I could dig on my archives if you want....

ShannonS
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Post by ShannonS » Mon Oct 22, 2012 2:52 pm

Do you know any decibel relation of the 0 ti 99 mapping ?

1 step in 0.75db on all 0...127 scale, 8 steps is 6db and so on.
I don't know the dB value and none of the manuals for the DX series give any indication. I think it's because it's combined with input key velocity (I send 100) and various keyboard scaling values in some esoteric way.
some years ago, I worked on TX81, FB01 and DX7 patch import (if I remember correctly the names)
I could dig on my archives if you want....
I would be interested to see how you mapped some of the parameters that don't match between the two.

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Post by ShannonS » Wed Oct 24, 2012 5:37 pm

After some deep googling I found a couple of references to converting patches from a DX series to the YM2612. One said map 0-99 to 127-0 linearly (I'm pretty sure this is wrong), another said they are the same scale and the lowest levels aren't used by the DX's and so zero for a DX is the same as 99 for the YM2612.

I think the scales are the same as it sounds much closer if I just map it directly setting the lower 28 levels to zero. One thing I have found is that bass sounds are much louder on the TX81Z than the YM2612. I'm not sure why this is, I've disabled all the key scaling on the TX81Z and they still sound way too loud (it might just be I'm not dynamically altering voices and the output level register is changed during playback).

Another minor issue is the envelopes on the YM2612 are a bit quicker than on the TX81Z but other than that they sound pretty damn close.

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TmEE co.(TM)
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Post by TmEE co.(TM) » Thu Oct 25, 2012 7:32 am

You got a different clock on 2612 which is why the envelopes are faster. If you use same clock for both you will got same results.
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ShannonS
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Post by ShannonS » Thu Oct 25, 2012 5:07 pm

You got a different clock on 2612 which is why the envelopes are faster. If you use same clock for both you will got same results.
Good point, I hadn't considered that. Hunting around I think the standard clock rate for DX series is 7.14 vs 7.67 so ~7% faster for the genesis.

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Post by commodorejohn » Fri Mar 08, 2013 3:36 am

Any progress on this? I just got a TX81Z myself, and I'd love to try out some Genesis tunes on it :)

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