nesdev.org

I really like retro consoles, computers and hardware in general. The old 8 and 16-bit systems have all kinds of restrictions, which in a way defines them and gives them character. Sometimes I like to make up my own retro systems, with their own quirks and make stuff with their limitations. This sound system is one of them. The PentaSound Chip is a part of a fictional 16-bit computer, called The MT Computer(real imaginative, I know). Unlike most 16-bit systems, which would use FM Synthesis for their audio, this one uses Subtractive Synthesis, much like the C64's SID chip.
The PentaSound Chip has a total of 5 sound channels. Each channel has one operator. The first four can be either Saw Waves or 50% Square Waves. The fifth one can be either a 50% Square Wave or Noise. Each channel can be put through a Low-pass filter and the level of Resonance can be changed. And that's pretty much it. I decided to leave out stuff like pitch range or the number of volume levels, since adding these restrictions can make it a pain in the ass to make music, especially when there is no specialized software for this. (Although I'd personally have either a 4-bit or a 6-bit value for each channel's volume)

I've made a cover of the Vampire Killer theme from Castlevania to showcase what the Pentasound chip can do. You can check it out here.

What do you think of the cover? What do you think of the idea of fictional sound chips, in general? Let me know your thoughts.

Thanks!

AlienX wrote:The first four can be either Saw Waves or 50% Square Waves.

How very analog of you. Basically sounds like an array of VCOs...

(Compare also SN-Voice)

The fifth one can be either a 50% Square Wave or Noise.

Ok, an LFSR that can be clocked by the square wave, sure. Vaguely like the DMG's noise channel.

Each channel can be put through a Low-pass filter and the level of Resonance can be changed.

Borrowing that part from the SID, sounds good.

(Compare also lft's Chipophone)

cover of the Vampire Killer theme from Castlevania

It's impressive how much this sounds like an OPL2 cover.

So far it sounds very Roland-inspired. Roland was a fan of subtractive synthesis, which it called Linear Arithmetic synthesis to hide the fact that it operates by taking things away from a wideband excitation.

AlienX wrote:Each channel has one operator. The first four can be either Saw Waves or 50% Square Waves. The fifth one can be either a 50% Square Wave or Noise.

Why not variable pulse width, like the NES has? I imagine that a convincing piano or acoustic guitar could be made by combining a 25% square wave with a decreasing LPF cutoff frequency.

I didn't expect a technical analysis of this.

But, yeah, I wanted this to be somewhat realistic, so I basically took what the SID chip had to offer, strip down some of its features, added two more channels and there you go. It's interesting how everyone was attracted to FM Synthesis at the time, but I guess analog filters might be more expensive. Anyway, after posting this idea on the Famitracker forums, I was proven, that a fictional sound chip doesn't have to be realistic. Lots of people started making up all kinds of interesting mixes. This one by Dr Devil uses a fictional sound chip, that combines Samples, FM Synthesis and PSG Channels.

lidnariq wrote:It's impressive how much this sounds like an OPL2 cover.

Yeah, I've noticed it too.

tepples wrote:So far it sounds very Roland-inspired. Roland was a fan of subtractive synthesis, which it called Linear Arithmetic synthesis to hide the fact that it operates by taking things away from a wideband excitation.

Yeah, but the Roland sound cards also had MIDI. (And, yes, Roland also made synthesizers, but I'm focusing on sound chips, that would be used in a video game console or a computer) I never thought about Roland's stuff when coming up with this idea, anyway. I like subtractive synthesis myself and wondered why no one made more sound chips specifically designed around subtractive synthesis, like the SID chip.

tepples wrote:Why not variable pulse width, like the NES has? I imagine that a convincing piano or acoustic guitar could be made by combining a 25% square wave with a decreasing cutoff frequency.

Well, originally it was because of the limitations, that the VST I was using provided. Then, when I switched over to another one, I thought about it, but decided to leave it as it is. Although this might be limiting, it makes you focus on what you could do with the Saw and Square Waves and it also gives the chip some character.

On a Yamaha FM synth, as the modulator's amplitude falls to 0, the output becomes a plain sine wave, similar to what you get when you run a sawtooth wave through a lowpass filter. It's in fact the 1x->1x patch, and the square wave is the 2x->1x patch. So yes, it's no coincidence that this sounds so similar to the OPL. It's that combined with that ~6hz vibrato that makes this sound so much like the OPL2 for me.

This is very nice; I'd be very impressed to find something that sounds like this in a late 80s/early 90s era computer or video game, and it would've been possible too.

The harmony is awfully wrong at 0:11 and 0:16

Otherwise, yeah it sounds very simlar to OPL2.

So many people are commenting on how OPL2 it sounds, but it really is striking how FM it does sound.

A few years ago I tried to make a very minimal music engine (minimal strictly in the sense of code size), and I used 2-op FM for it; one of the great things there was that you can make white noise on any channel with a very simple FM feedback operation (though the caveat is that this noise basically only has one colour). Video here: bunchbox 4k demo

For your particular engine, I'd actually suggest that you give the noise a different kind of tone control than just the resonant filter everything else has. I don't think filtered noise really has much interesting variety to it. The NES is a really good example, actually, because it's a sample-and-hold the lower noise rates end up producing a lot of spurious harmonics via the square shape of the noise pulses; this adds some distinct character that's rather useful.

Pulse width was another good suggestion for the square channels, a simple device that has a lot of variety.

A simple echo can go a long way; it's amazing how characteristic the SNES' limited echo with a weak filter became to that system.

Ring modulation might be interesting, like if you allowed the result of one channel to ring modulate with the previous one. SID could do this to some extent. I don't think it's a typical "video game" sound, but it can produce a lot of neat "electronic" noises which are probably suitable for games anyway. AY could kinda do ring mod by combining the buzzer with a square channel, as well, but not many composers did this. Actually, I guess the noise + square modes of the AY are technically a form of ring modulation too.

Drag wrote:On a Yamaha FM synth, as the modulator's amplitude falls to 0, the output becomes a plain sine wave, similar to what you get when you run a sawtooth wave through a lowpass filter. It's in fact the 1x->1x patch

Yeah, although the patch sounds a little differently than a saw wave, so I decided not to make the comparison. They do sound quite similar though.

Bregalad wrote:The harmony is awfully wrong at 0:11 and 0:16

Well, so much for me, trying to make a counterpoint melody. I actually thought, that this part fits the rest of the composition better than the other parts. It's just that it sticks out too much.

While all the suggestions for the sound chip's features are nice, I am not going to change it. I've already established how it sounds and making changes will just ruin any consistency between the songs, that I make with it. I will save the suggestions for other sound chips.

rainwarrior wrote:I don't think filtered noise really has much interesting variety to it.

A sufficiently high-Q resonant filter is actually kinda fun with a noise source:

True, the "resonant" part of it does help, especially with envelopes.

I enjoyed this cover quite a bit. I liked your countermelody btw...there's no such thing as "wrong" in music, unless you specifically set out to follow perfect part writing rules or something (which a lot of video game music violates all over the place, and nobody cares because it sounds good anyway).

I like the idea of fictional chips and computers. I think if retro homebrew ever becomes less viable to participate in (i.e. no market, no scene, etc. etc.), I very well might create a "fake" emulator for an NES-like computer and write games against it. I just find it more fun to work in that sort of environment. Whether virtual or not, the feeling of coding for that sort of ecosystem would be the same.

Exactly! In fact, most of the games I'm planning to make will be based around the fictional computers I've created. I won't make emulators for them though. For me, it'd be easier to make each game have its own executable.
I don't think this idea should be tackled only if the homebrew scene dies off. It could become its own thing and coexist with the homebrew games on real systems.

Yeah, absolutely...I only meant for me personally, I'm quite happy continuing to develop for the NES---lots of momentum gets built up over time from experience and tools and such. But should there ever be a strong reason to abandon development for real NES hardware someday, it's definitely something I'd consider.

So what you mean is really designing a fictional computer and then writing a game based around its constraints rather than actually building a virtual machine that guarantees execution according to that fictional computer's design? I guess for me personally I'd definitely go the virtual machine route (but still bake it into a game'e executable rather than make the emulator available separately...) because I find it so fun to write assembly language for older processors.

It'd be fun to create a 3D animation (splash screen) of a cartridge getting inserted into the fictional computer, and then show a crt TV and then it zooms in full screen and gameplay begins, haha.

Well, I'm not really good at programming, so I won't be able to make a virtual machine anyway. And even if I was, this would create all sorts of limitations, when it comes to programming. When making games, I prefer using specialized software, because it's much faster and, again, I'm not good at programming. A virtual machine for a fictional computer would be really cool, though.

PENTASOUND Cover!



I finally finished the Mission 1 Theme from Double Dragon! I decided to make it more like the Arcade version. This would also make sense, if the MT Computer, which uses the Pentasound chip, was an actual computer, because if Double Dragon came out for it, it would've been an arcade port. I think this cover shows off the Pentasound chip's capabilities more than the Vampire Killer cover.
You can listen to it here!

Is this cover good? What are your thoughts and criticisms for it? Which version of this theme do you prefer, in general? The NES version or the Arcade version? Let me know.

Thanks!