[music-dsp] a question about reducing calculation-complexity in a modular synthesizer

[Michael Gogins]

The 1 : 5 ratio was with Csound running with ksmps=1 and ksmps = something (10? 100? don't recall, but I have a spreadsheet at home that I will look at again).

Csound iterates ksmps frames over every dsp inner loop. So, with ksmps =1 , it's for(i=0; i < 1; i++) and with ksmps = 100, it's for (i=0; i<100; i++).  In other words the loop structure is identical, the only difference is dwelling in the inner loops longer, or not.

The C++ code I was referring to implemented the same DSP algorithms with sample by sample loops, so, as one would expect, it was a bit faster than Csound with ksmps=1.

Regards,
Mike

-----Original Message-----
From: robert bristow-johnson <rbj at audioimagination.com>
Sent: Dec 12, 2005 12:05 PM
To: music-dsp <music-dsp at ceait.calarts.edu>
Subject: Re: [music-dsp] a question about reducing calculation-complexity in	a modular synthesizer


----- Original Message -----
From: "Vesa Norilo" <vesa.norilo at saunalahti.fi>
To: "music-dsp" <music-dsp at ceait.calarts.edu>
Subject: Re: [music-dsp] a question about reducing calculation-complexity in a modular synthesizer
Date: Mon, 12 Dec 2005 11:22:26 +0000

> > I think single sample code can be made faster than it is typically  
> > written. I did some tests a few years ago using machine generated C code. 
> > Block processing was usually faster, but not by 5 times, and it  depended 
> > on what was being done and how things were divided up.
> 
> I'd like to point out that in some cases, sample-by-sample processing makes 
> it possible to keep everything in the CPU registers - in that case, block 
> processing could well be slower.

sure, that sounds like a dedicated device doing a single function.  for a modular synth or modular processor, where the modules are likely doing all sorts of different functions, i doubt that you would be able to get away with not saving and restoring the context of the CPU for *each* module.  it's the cost of that saving/restoring that gets reduced by using block processing (but i doubt it's a 5 fold savings, maybe 2 or less).

--

r b-j                  rbj at audioimagination.com

"Imagination is more important than knowledge."

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