Synthesis in the Open Source World

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Synthesis in the Open Source World

Postby Consul » Tue Mar 11, 2008 3:15 am

A fellow I know from online has coded and released an inexpensive but still commercial softsynth here:

http://www.stillwellaudio.com/?page_id=37

How does it sound? It completely blows me away, which is much, much more than I can say for any OSS softsynth I've auditioned (I'm not counting LinuxSampler here, as any sampler is dependent mostly on libraries, so I'm limiting myself to synths that generate all of their sound internally). I'm getting a little tired of OSS audio developers who think that Linux music ends with being able to record a band.

I'm making it my mission to kick-start and create the next generation of soft-synths for Linux. As Schwa's Olga synth proves, non-linear characteristics are equally as important to the sound of a good synth, and need to be considered in design. He also proves that one person can put together such a beast in a reasonable amount of time (a second person did the artwork, but that has little to do with the rest of my argument).

Rant over. Sorry for the distraction.
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Re: Synthesis in the Open Source World

Postby Alex » Tue Mar 11, 2008 2:47 pm

Darren,
You get my vote. Anything that produces the same sort of results as Schwa's 'Olga' can only be a worthwhile addition to the linux audio armoury.

Alex.

:)
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Re: Synthesis in the Open Source World

Postby Consul » Tue Mar 11, 2008 4:58 pm

Schwa's really hit a home run with that one. Olga alone is enough to make me consider dropping OSS and going back to Reaper and VSTs. Again, that highlights what I feel is a sad state of affairs in the open source synthesis world. You'd think some upstart would have already come along and kicked the Linux audio world in the ass over the poor choice of synthesis capability. It looks like I might have to be that upstart.

Again, please keep in mind I'm not talking about sampling here.
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Re: Synthesis in the Open Source World

Postby lowkey » Tue Mar 11, 2008 6:38 pm

Olga is pretty amazing. It's so good I almost re thought my "no more VST's" mission lol
Im sticking with LinuxSampler and ReNoise but I wish ya well Consul. A synth of this quality would be brilliant for Linux.
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Re: Synthesis in the Open Source World

Postby Consul » Wed Mar 12, 2008 10:59 pm

I've posted the link to this paper before, but this describes a way to model both linear and non-linear aspects of a circuit:

http://ccrma.stanford.edu/~dtyeh/papers ... ortion.pdf

Mr. Yeh focused this paper on distortion pedals, where it's easy to determine which elements of the circuit are linear and which are non-linear. In more complex filter, amp, and oscillator circuits, it becomes harder to determine which parts are which.

In the case of the Moog ladder filter, there is actual overload protection built into the ladder section, so the filter distorts in a predictable manner. Finding and isolating the transfer function for that part becomes the task, then, along with parameterizing it. The TB303 filter has a unique set up, in that it has a self-oscillation protection circuit as part of its feedback section, which prevents it from (surprise!) self-oscillating. What it does instead, is soaks up the extra power, resulting in a distinctive distortion which is the love of dance music and acid composers everywhere. This can be effectively emulated by placing a wave shaper with the appropriate transfer function within the filter's feedback loop. The filter in one of FLStudio's synths actually exposes this waveshaper with further parameterization, as opposed to Olga where the only control you get is how hard you want to drive the next section from the previous.

Clearly, Schwa has put a lot of work in making his non-linear functions sound really good. I don't know if he's implementing them as strategically-placed waveshapers, or if he's actually figured out how to numerically solve for a system of linear and non-linear differential equation, but if it's the latter, he might have a shot at the Fields Medal! (Linear and non-linear diff eqs together in the same system of equations is one of the most difficult things that can be done in mathematics, according to one of my instructors.) Of course, I suppose there are other methods of combining linear and non-linear elements. Non-linearities in analog circuits are typically caused by hysteresis effects, which are memory effects that certain components have. Using memoryless waveshapers to emulate those transfer functions is at best an emulation, rather than an actual modeling of the effect.

I've been playing with SAGE, which is an open-source mathematics package that ties together many other math packages together under a nice Python interface. With it, I've been playing with sets of non-linear equations, and sets of differential equations. I don't know how to actually do such math myself, but if I can figure out what to tell the computer, I'll just let it do the hard work and hand me a set of numeric functions I can implement. :D That's the theory, anyway. (It actually has built-in functions for doing Z transforms and Laplace transforms on sets. which is really handy.)

Now I just need to figure out what to tell it.
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