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Just a totally whimsical question, I am just guessing here but I would ASSUME a Sawtooth is computationally cheaper than a Tri. I think the 2A03 was a custom chip for the NES so I understand pulse channels are uber cheap cycle wise so I get why we have 2 of those fellas and I assume sine waves are move expensive?
So the question, why a triangle wave?
I'm curious about that question too. Anyone?
Purely for a good balance of timbres, perhaps?
If it's more difficult to compute than a saw then is that why the volume control is nearly nonexistant?
Hmm, great question. Nintendo tends to be quite holistic when it comes to design, so while the 2A03 is not an incredibly sophisticated chip even by that age's standards, perhaps they saw (hoho) the value of contrast that a triangle channel would bring as opposed to a saw? Interesting question no matter what the answer. Which makes me wonder: is there any other soundchip that has a set-in-stone triangle channel, barring chips that can sample or have custom waveforms? None comes to my mind...
Purely for a good balance of timbres, perhaps?
If it's more difficult to compute than a saw then is that why the volume control is nearly nonexistant?
this is what I thought too. a 12.5 pulse takes care of the harsher tones. but a triangle handles smooth flute-ish sounds and the lack of upper harmonics meant smoother bass that didn't interfere with the mids.
Last edited by 9H05T (Jul 5, 2012 2:51 am)
this may sound dumb, but: what is meant by 'computationaly cheaper' ??
My guess is the timbre balance too.
I would rather ask why NES doesn't have both saw and triangle, actually - when you have a triangle generator, throwing in a saw mode would cost next to nothing.
Triangle generator is not too different compared to saw - the same binary counter and a DAC, the only difference is that the most significant bit of the counter should invert output of the DAC. To combine both, a register-controlled gate that disconnects the MSB would be required (saw pitch is twice higher than triangle in this case).
Sine is more expensive, as it requires a ROM thrown in between the counter and DAC. However, this would enable arbitrary waveforms, defined by contents of the ROM.
This is quite an interesting question.
I think by computionaly cheaper means easier to generate than a saw. But then, i guess that too. Why male models?
this may sound dumb, but: what is meant by 'computationaly cheaper' ??
i think it means it takes less processing power/ram/rom whatever.
It's not necessarily any cheaper/easier to make a saw than a triangle the way they did it. The triangle wave generator is not a CPU running a program; it is a collection of logic that outputs to a DAC, so there is no "processing" or "computation" time in that sense. Oscillators on the 2A03 are not sharing a common processor resource (i.e. time); each one runs in parallel.
I'm not sure whether a saw wave generator would have taken less logic parts, but my intuition is that the difference in this case would have been negligible. I'm certain the VRC6 saw wave has a lot more logic components than the 2A03 triangle.
9H0ST I think has the best explanation. A saw has very strong harmonics which make it harder to blend with other sounds. The triangle is preferred for bassline for the same reason that a bass guitar is usually preferred to a baritone saxophone for this purpose. Similarly, consider a saw wave with no volume control like the triangle. This would probably be about the same level of complexity to implement, but imagine how hard it would be to balance with the other channels. Triangle is pretty hard to balance already, but at least because its audible bandwidth is mostly underneath/separate from the pulse channels it's manageable.
The triangle has no volume control, because it's built very similarly to the pulse channels. Each of these has a 4-bit output; in the case of pulses the DAC is either the square's volume setting or 0. In the case of the triangle, the shape of the triangle has 16 steps, already using its 4-bits of output. It'd be a lot of extra parts to be able to control its volume (you'd need an 8-bit output, and some logic to control the amplitude).
fluidvolt: They actually made a few bad design decisions on the 2A03. The DPCM frequency table is particularly poorly chosen, in my opinion. The length counter table is somewhat useless, as well. The DPCM also conflicts with the data bus used by controllers, so games that use DPCM have to read the controller state 3 times every frame to prevent bad button-press data. (Interesting thread at NESDev about DPCM frequencies here.)
Last edited by rainwarrior (Jul 5, 2012 7:29 am)
going in line with everything Rainwarrior just said, it's my best guess that the people who made the sound chip wanted the nes to have the closest thing to a pure tone (sine wave) as possible, which turned out to be a triangle wave.
Was going to say what Shiru and rainwarrior said, but they already said it. My "alternative" theory is that the NES was a kid's console and that they avoided using a sawtooth wave because sawtooth waves are sharp, and the kids might get hurt.
