Re: [Linuxsampler-devel] envelopes, events, Re: LS click/pop investigation

[Steve H. <S.W...@ec...>]

On Tue, Dec 30, 2003 at 02:19:10PM -0300, Juan Linietsky wrote:
> First, considering that a segment size is between 50 and 100 samples,
> updating the values between segments and ramping linearly inbetween (being the 
> enveloped curved or not) will make absolutely NO audible difference than 
> using a lowpass (I've implemented this several times, and I composed a few 
> hundred of songs with the code :), and considering that this is the most
> critical part of the whole app, I have to say that i'm against adding more 
> code in there. The segments are too small already, much smaller than the
> delta times between envelope points.

I think 50-100 samples is too few - for fast attachs it definatly wont be
enough. I think 32 is quite a common value.
 
> I also read somewhere in the thread that updating every a few (4) samples
> would be a good idea, but I have to remind you that adding any
> kind of conditional inside the critical loop reduces the performance
> enormously in modern procesors, I believe this is because it stalls
> the instruction pipeline.

You can roll it in with the loop termination condition, but I'd agree that
4 is too often. Someone could benchmark it to find where theres a sweet
spot. This would be a good candidate for SIMD instruction optimisation, to
run 4 enevelopes at once.

- Steve