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Apparently the game Skitchin' gets 4 voice polyphony out of one sample channel thanks to Kevin Pickell. They used 2bit samples and only one of the channels was capable of changing pitch (the guitar). Dino and I were hanging out so we asked Jeff Van Dyke about it on twitter.
Last edited by animalstyle (Nov 11, 2013 5:31 pm)
I don't get it. You can write whatever you want into the PCM channel, a wav of a 4 strings chord for example or have separates sounds and sum them all. What's exactly the interesting part of this?, there's a source code example out there?
We were watching it on the GensKmod's debug section and we were getting pretty confused. There was so much overlap that we didn't understand how the sample guitar was shifting pitch but the drums weren't. There would be too much room taken up if every guitar note was a different sample.
Maybe realtime software mixing is a challenge? Pitch shifting would have to be done in software too I think.
I don't get it. You can write whatever you want into the PCM channel, a wav of a 4 strings chord for example or have separates sounds and sum them all. What's exactly the interesting part of this?, there's a source code example out there?
Right but you probably have a limited amount of memory to store samples, so having the ability to get multiple notes out of 4 samples is interesting versus just brute force sampling tons of guitar chords to use.
Delek wrote:I don't get it. You can write whatever you want into the PCM channel, a wav of a 4 strings chord for example or have separates sounds and sum them all. What's exactly the interesting part of this?, there's a source code example out there?
Right but you probably have a limited amount of memory to store samples, so having the ability to get multiple notes out of 4 samples is interesting versus just brute force sampling tons of guitar chords to use.
yea totally. The sound design on that game soundtrack is pretty fuckin genious. Definitely an extension of the Skate or Die aesthetic!
Yeah it is a nice feature 
especially thinking that you can also create some small looping pcm data with virtually no memory to create new waveforms channels....then, read x samples from the rom >> handle playback rate >> mix them in an output buffer >> output the obtained sample to the DAC
There is an implementation of something like this here for example https://code.google.com/p/sgdk/source/b … 0_drv4.s80
(no playback rate support though)
It was found back in 2009 that Toy Story basically has a 4-channel SEGA Genesis MOD player that uses the DAC. Perhaps Skitchin' uses a similar engine?
It was found back in 2009 that Toy Story basically has a 4-channel SEGA Genesis MOD player that uses the DAC. Perhaps Skitchin' uses a similar engine?
Didn't know about that one... pretty cool info. Thanks! I probably never realized because i usually skip over the Disney shit. 
I doubt its the same engine. I can't see Disney working with the guys who created Road Rash and Skitchin.
What a waste of ROM memory that Disney choice, too much programming effort for nothing. They did also a pure FM version of "You've got a friend in me", it is present in the storyline in the end of the game!, it sounds a lot better!
Interesting the .mod playback thing, but a very strange idea to only use it for one track that is later re-done in the native system architecture.
Last edited by Delek (Nov 17, 2013 3:25 am)
That mod stuff is pretty interesting. Seems really strange but certainly unique sounding. I actually like the mod version better then the FM. The FM feels pretty flat to me and uninspired. The mod version maybe more noisy but it does certainly feel more dynamic. To me it would feel like a nice treat to hear something that different sounding coming from my genesis/megadrive. I mean, hearing an simple voice sample in video games at the time was pretty cool. It would certainly be much cooler way to reward your players for making the end credits then more of the same and text. Also considering how the SNES was boasting about how superior its audio was using samples... Yeah I think it was totally worth it.
FM:
IMO, A better choice would have been to make a mix of FM + Mod...
keep samples for layered drums with gated and reverberated stuffs and boost it up with FM on top (basically a drum layering)
Another cool trick is to use samples only for the attack or sustain transient part of the FM sound...very powerful when FM alone cannot produce a particular sound.
combination of both is better than only FM or only PCM but as a whole FM is still preferable on the Genesis because well...the system is FM powered
IMO, A better choice would have been to make a mix of FM + Mod...
keep samples for layered drums with gated and reverberated stuffs and boost it up with FM on top (basically a drum layering)
yes - thats what Skitchin' does at times. there is some FM bass and an FM lead (and echo) that comes in... the PSG is used for the noise channel at times (i think) for sound effects. Also I think there are some ride sounds being produced by the 2612. Jeff Van Dyke knew what he was doing!
Last edited by animalstyle (Nov 19, 2013 7:55 am)
I can agree with that. I love that radnessss. that transient trick is a good one. I have used it in other things when synthesizing sounds on my laptop but never thought to try it on chip hardware.
One thing that i noticed in the FM world that i miss about the subtractive synthesis is that there is a strong emphasis on trying to recreate real life instruments. Personally I favor letting the FM be its own sound. For me the sound replication always ends up sounding boring and generally cheesey. It wasn't until i heard those "BRAAAAAAAAAG" and "TWAAAAANG" soundeffects that i got into FM synthesis. Ultimately thats why I ended up liking the mod version of this better.
The genesis/megadrive was such a powerful machine sound wise. It has so much potential. It has soooo many modern applications in music production. I mean the polyphony trick is totally proof of that. It really does stand out as its own instrument.
Last edited by wedanced (Nov 21, 2013 10:26 pm)
Lol those written out sound examples probably do nothing for anyone.
https://soundcloud.com/e-n-cowell/giraf … e-n-cowell
I don't have a really good sample on hand but those bass sounds I made around 1:30 or so are kinda the FM synthesis i am talking about. This has been produced hardcore so it is probably hard to hear but I could totally make that on a genesis. Buuuut whatever. I wont subject you guys to my ramblings any more.
I can agree with that. I love that radnessss. that transient trick is a good one. I have used it in other things when synthesizing sounds on my laptop but never thought to try it on chip hardware.
One thing that i noticed in the FM world that i miss about the subtractive synthesis is that there is a strong emphasis on trying to recreate real life instruments. Personally I favor letting the FM be its own sound. For me the sound replication always ends up sounding boring and generally cheesey. It wasn't until i heard those "BRAAAAAAAAAG" and "TWAAAAANG" soundeffects that i got into FM synthesis. Ultimately thats why I ended up liking the mod version of this better.
The genesis/megadrive was such a powerful machine sound wise. It has so much potential. It has soooo many modern applications in music production. I mean the polyphony trick is totally proof of that. It really does stand out as its own instrument.
I agree with that FM really got its own sound especially when you do some real time modulation, the YM2612 also got the SSG envelopes witch are looping ones (the looping can reach audio rate!)
One example demo here(only FM + PSG) with a modulated lead (3 channels) https://soundcloud.com/alyjameslab/ym26 … ve-vst-psg
And some FM +SSG envelope + CSM >> https://soundcloud.com/alyjameslab/glitches-brew
Last edited by Aly James (Nov 30, 2013 3:24 am)