[sdiy] BLIT/BLEP virtual analogue synthesis

[Antti Huovilainen]

On Tue, 3 Aug 2010, Tom Wiltshire wrote:

> Has anyone on the list played with either of the above techniques?
>
> https://ccrma.stanford.edu/~stilti/papers/blit.pdf
> http://www.cs.cmu.edu/~eli/papers/icmc01-hardsync.pdf

Does coauthoring this count? ;)
http://ieeexplore.ieee.org/search/srchabstract.jsp?arnumber=4117934&isnumber=4116828&punumber=79&k2dockey=4117934@ieeejrns&query=%28%28valimaki+v.%29%3Cin%3Eau+%29&pos=1

(V. Välimäki and A. Huovilainen, "Antialiasing oscillators in subtractive 
synthesis," IEEE Signal Processing Magazine, vol. 24, no. 2, pp. 116.125, 
March 2007.)

I can send a copy of the draft to interested people, but can't put it up 
for public access. Also see my Master's Thesis:
http://users.tkk.fi/~ajhuovil/Huovilainen_MastersThesis.pdf

> I've been reading the papers (the two classics above amongst others) and 
> doing some experiments, and it seems to me that getting decent results 
> at low sample rates (like 44.1KHz) is still really difficult. For 
> example, a 8KHz tone is going to have about 5.5 samples per period at 
> 44.1KHz. This doesn't seem like enough to represent anything much, 
> nyquist theory notwithstanding.

5.5 samples is enough to represent two harmonics which are the only 
audible harmonics for a 8 kHz sawtooth. Ignore your gut feeling and trust 
Nyquist (remember: audio DAC has a very steep digital lowpass filter which 
removes the image frequencies and hence the jaggies in the output 
waveform).

> If you've some experience to share, I'd be interested to discuss this, 
> either on or off-list.

Ignore BLIT and minimum phase BLEP and stick to pure BLEP. BLIT has 
numerical and stability issues and minimum phase BLEP is in 9%% of cases 
only a pointless complication (it does not remove lookahead like Brandt's 
paper claims).

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova