[LAD] panning thoughts

[Ralf Mardorf]

On Sat, 2010-11-13 at 19:30 +0100, Arnold Krille wrote:
> On Saturday 13 November 2010 18:51:17 Ralf Mardorf wrote:
> > On Sat, 2010-11-13 at 16:26 +0100, fons at kokkinizita.net wrote:
> > > On Sat, Nov 13, 2010 at 02:57:44PM +0000, Folderol wrote:
> > > > Paul Davis <paul at linuxaudiosystems.com> wrote:
> > > > > there's an awful lot of math for which a modern processor can compute
> > > > > the answer faster than it can look it up. this is one such example
> > > > > (as fons noted), but there are many others. this started changing
> > > > > about 8 years ago, and its only gotten more true since then.
> > > > 
> > > > Oh dear. I didn't realise I was so far out of date :(
> > > 
> > > It's absolutely true.
> > > 
> > > Note that the calculation I posted earlier runs entirely on
> > > the FP processor, and two variables, q and d, will probably
> > > only exist there and never be written to memory. If it takes
> > > any time at all, the CPU can meanwhile do something else,
> > > such as getting the pointers to the audio data it will need
> > > later. Using a LUT will mean the CPU has to do all the work,
> > > which includes getting the base pointer and calculating the
> > > required offset(s).
> > Just to ensure you aren't talking about different claims.
> > 
> > Is math even faster, as e.g. 4 states for left, 1 for centre and 4
> > states for right, provided e.g. by an array? Or are you thinking about
> > nearly stepless panning?
> 
> Unless your memory runs (and is connected) at the same speed of the processor 
> (which afaik no platform has, even the first and second cache run at lower 
> speeds), simple math of only a limited number of operations is always faster 
> then getting stuff from memory. Todays processors contain even more 
> optimizations for fast and parallelized math.
> The trick Fons showed is about doing the pan calculations in simple math 
> instead of using trigonometry which would require complicated functions like 
> sin/cos to be called or tables from memory to be checked.
> 
> Have fun,
> 
> Arnold

Using sin/cos still is very time-consuming?

I do understand The Wiki on German better, but the Wiki on English,
pardon:

"Die Tabellierung aller Werte ist angezeigt bei
geschwindigkeitskritischen Echtzeit-Anwendungen, wenn diese nur eine
recht kleine Winkelauflösung
benötigen." (http://de.wikipedia.org/wiki/Sinus_und_Kosinus#Berechnung)

Loosely translated: Tabulation for rt (when using sin/cos) for small
angles (what ever a small angle might be) is still faster.

My question: It's better to avoid using sin/cos and instead to use Fon's
trick?!

Hence Qtractor (Rui) better shouldn't use sin/cos?

Thanx,

Ralf