[vnorilo]

Running the oscillators at a ridicilously high rate allows the use of non-bandlimited, trivial algorithms. Band-limiting is not a solved problem, all the algorithms get messy in different dynamic scenarios. As to why design a custom FPGA bitstream for this? It could actually be a reasonable fit if you actually make the waveform generators directly in the LUTs and latches and run the whole thing at 24MHz.

[klodolph]

Can you give an example of one of these algorithms you’re talking about? I don’t understand why these would work at 512x but not at, say, 4x or 16x.

[vnorilo]

At 4x you would need something like poly-blep with 24/32-bit fixed or floating point support to generate a nice bandlimited sawtooth. Features like oscillator sync can still cause problems. I recall hearing at Clavia HQ that the original Nord Lead used 16x oversampling with a naive generator (subject to hearing it once and my memory over 15 years). Upping to 512x can be reasonable on a fpga, where you can aggressively minimize wordlength and match the DAC. Is there any advantage over say 32x? Maybe not, but feeding the DAC 1:1 can save some complexity.

Edit: So I envision the ultra high rate sawtooth as essentially a n.m bit fixed point accumulator wrapping around by itself, with the n-bit (4? 8?) top part going over to the DAC as a kind of directly generated DXD format signal.

[klodolph]

So the only advantage is that you can feed the DAC 1:1?

FPGAs are difficult to program, that’s a pretty steep cost to save you the trouble of downsampling your signal, something which is already pretty damn easy to do.

16x oversampling is fine, DSPs are fine. DXD is snake oil.

[vnorilo]

Sure you can make an equally good synth without fpgas or dxd. I'm not trying to sell you this design. However it's educational to think about when and how it makes technical sense. I do agree that marketing turns it into brain damaged bullet points pretty often.

[diydsp]

you've got to think outside the box. with fpga, we can get into new algs like variable-sized lattice gas synthesis.