[Yalecsa]

Hello, I'm currently in the process of re-arranging existing music into sounding as if it were played on a Mega Drive, while trying to obey all the rules of the actual Mega Drive (5 FM synth, 1 DAC, 3 PSG, 1 noise). I'm only making use of soundfonts and VOPM at the moment, as I'm a bit of an amateur, and getting to grips with the actual VGM format and the programs associated with it is slightly terrifying. So I'll save questions about mid2smps and the like for another time. For now, I was wondering if anyone could help me with the following.

Firstly, I've been experimenting with creating drum sounds using the FM synth channels. I know a few Mega Drive games use the FM channels for percussion, either to keep the DAC channel free for sound effects, or to play multiple drum sounds at a time. I was wondering if anyone had some good examples of this? Specifically, bass drums, kick drums, that kind of thing. The Mega Drive is great for bassy sounds in general, so my head tells me it must be able to produce a good kick drum sound via FM synth, surely?

Secondly, once an instrument has been set on one of the FM synth channels, and the music is playing, can the instrument be changed, mid-song? This would obviously be a very useful thing to do, but I've not seen any examples of it in any of the Mega Drive games I've looked at. Is it even possible to do on a technical level without interrupting the song?

Thirdly, I've seen the odd Master System game play (low quality) voice clips, using all its sound channels at once. Theoretically, as the Mega Drive's PSG and noise channels are the same as the Master System's, could it be used for samples during music? It would obviously be very low quality, and at the expense of four audio channels, so may not be worth it most of the time. But it would be a neat trick to pull out for the odd song.

And finally, can samples played by the DAC change in pitch mid-song? I'm aware of the "Sunsoft bass" technique used on the NES, whereby bass guitar sounds were played through the sample channel of the NES at different pitches to simulate a good bass sound, as in Journey to Silius. Can something similar be done via the Mega Drive's DAC channel? ... And I suppose I should also ask if it can be done on the Master System's sound chip when playing samples, though that's only really necessary if the answer to question three is affirmed.

If anyone has any answers to any of the above, it'd be greatly appreciated! />

[GerbilSoft]

I'm not that well-versed with the YM2612, but I can answer some of your questions:

Yalecsa, on 08 July 2015 - 07:51 AM, said:

Secondly, once an instrument has been set on one of the FM synth channels, and the music is playing, can the instrument be changed, mid-song? This would obviously be a very useful thing to do, but I've not seen any examples of it in any of the Mega Drive games I've looked at. Is it even possible to do on a technical level without interrupting the song?

I don't know if any of the well-known sound programs for MD support this, but it is doable. Just rewrite the channel's configuration midway during the song. Each channel has its own set of registers, so this shouldn't cause problems.

Yalecsa, on 08 July 2015 - 07:51 AM, said:

Thirdly, I've seen the odd Master System game play (low quality) voice clips, using all its sound channels at once. Theoretically, as the Mega Drive's PSG and noise channels are the same as the Master System's, could it be used for samples during music? It would obviously be very low quality, and at the expense of four audio channels, so may not be worth it most of the time. But it would be a neat trick to pull out for the odd song.

It is possible, but PCM emulation using the PSG is low quality due to the fact that the PSG volume levels are non-linear. The other option is PWM, which allows for a linear volume scale but requires a much higher sampling rate for the same quality as PCM. See http://www.smspower....SamplesOnThePSG for more information.

Yalecsa, on 08 July 2015 - 07:51 AM, said:

And finally, can samples played by the DAC change in pitch mid-song? I'm aware of the "Sunsoft bass" technique used on the NES, whereby bass guitar sounds were played through the sample channel of the NES at different pitches to simulate a good bass sound, as in Journey to Silius. Can something similar be done via the Mega Drive's DAC channel? ... And I suppose I should also ask if it can be done on the Master System's sound chip when playing samples, though that's only really necessary if the answer to question three is affirmed.

Pitch adjustment is done by changing the frequency of which the samples are output, e.g. skipping every few samples to increase the pitch or repeating a couple samples to decrease the pitch. The DAC doesn't have any sort of sample RAM; it's literally just a single output. Whatever you write to it gets converted to an analog signal and is placed on the audio output lines.

Sidenote: Sega CD's PCM chip does have sample memory, as well as a frequency control register that basically controls how fast the address counter increments. Make it go faster than the expected frequency, and the pitch goes up; make it go slower, and the pitch goes down. Note that this register is actually fixed-point decimal; there's 11 digits after the decimal point, which allows for fine-tuning of the pitch. Obviously only the address to the left of the decimal point is used for determining the RAM address, but since it allows for a fractional increment, you can adjust the pitch much more finely than a simple power-of-two increment/decrement.

[nineko]

Yalecsa, on 08 July 2015 - 07:51 AM, said:

Firstly, I've been experimenting with creating drum sounds using the FM synth channels. I know a few Mega Drive games use the FM channels for percussion, either to keep the DAC channel free for sound effects, or to play multiple drum sounds at a time. I was wondering if anyone had some good examples of this? Specifically, bass drums, kick drums, that kind of thing. The Mega Drive is great for bassy sounds in general, so my head tells me it must be able to produce a good kick drum sound via FM synth, surely?

Aside from a handful of official games (which I can link you to, of course), you should know that some sceners around here are very talented with FM drums. For example, you should look at the stuff done by the user "Crash" in the SMPS music competition.

Yalecsa, on 08 July 2015 - 07:51 AM, said:

Secondly, once an instrument has been set on one of the FM synth channels, and the music is playing, can the instrument be changed, mid-song? This would obviously be a very useful thing to do, but I've not seen any examples of it in any of the Mega Drive games I've looked at. Is it even possible to do on a technical level without interrupting the song?

Yes. There are at least two drivers (smps and Cube) which allow for that. There is no reason not to allow for that. Any register can be rewritten at any given time.

[Yalecsa]

Oh you guys, that answers everything I needed to know, and gives me a whole bunch of interesting reading to do, too! It sounds like a lot of the things I want to do would technically be possible on a Mega Drive. But, maybe not for a simpleton like me. Maybe in the future, when I'm a bit better versed on the tech aspects, I might give some of it a go. In the meanwhile, I'll stick to soundfonts and VOPM, and pretend I'm going for an "authentic to the time" sound rather than showcasing what the Mega Drive is theoretically capable of audio wise. :3

Oh, but I would so love to try and use FM synth drums, the DAC, Master System PCM/PWM, and the noise channel all together to create a fake drumset for some Mega Drive style heavy metal, ahaha. Maybe one day.

Thanks again guys, super informative! />

[vectrexian]

You might want to give Deflemask Tracker a try once you want to move on to producing VGM files. The UI isn't too bad and it's generally a pretty good program. It also supports other consoles besides the Genesis/MD, which is quite nice. Good luck with your Sega music endeavor, it's always nice to hear some new Genesis chiptunes!

[rata]

Yalecsa, on 08 July 2015 - 11:37 AM, said:

Oh you guys, that answers everything I needed to know, and gives me a whole bunch of interesting reading to do, too! It sounds like a lot of the things I want to do would technically be possible on a Mega Drive. But, maybe not for a simpleton like me. Maybe in the future, when I'm a bit better versed on the tech aspects, I might give some of it a go. In the meanwhile, I'll stick to soundfonts and VOPM, and pretend I'm going for an "authentic to the time" sound rather than showcasing what the Mega Drive is theoretically capable of audio wise. :3

Oh, but I would so love to try and use FM synth drums, the DAC, Master System PCM/PWM, and the noise channel all together to create a fake drumset for some Mega Drive style heavy metal, ahaha. Maybe one day.

Thanks again guys, super informative! //forums.sonicretro.org/public/style_emoticons/default/smile.png/>

Decap Attack and Saint Sword both use FM Synth drums and can give you an idea of how YM2612 power metal can sound like.

Battletoads - Turbo Tunnel Race (PSG cymbals) (very Deep Purple like)

Decap Attack - Intro (Synth drums at YM Channel 3)

Saint Sword - Gorgon's Theme (Synth Drums at channel 2)