On Wed, May 01, 2013 at 04:29:46PM -0500, David Pickett wrote: > At 16:02 01-05-13, Fons Adriaensen wrote: > > >The difficult part in writing any software emulation of the Dolby-A > >or similar systems is modelling the dynamic behaviour of the compander, > >not the actual audio processing. Such systems will have 'designed' and > >documented attack/release times, but analog electronics being what they > >are, the dynamic behaviour of the compressors and expanders will very > >probably not fit to any simple equations. Nor does it have to: the way > >Dolby-A and Telcom switch between encoding and decoding (by making the > >decoding algorithm the mirror image of the encoding) guarantees that > >the two will cancel each other, whatever they are. > > So, analog still rules!
For some value of 'rules' :-) Fact is that some simple analog circuits are quite difficult to emulate exactly in software, for the simple reason that they are 'imperfect'. Take a simple attack time circuit in a compressor. Could be a condensor being charged by a diode and resistance in series. The diode is not 'perfect', it will have some voltage drop depending on the current flowing in it. The result may well be 'desirable', i.e. in practice better than what would be obtained by using a 'perfect' diode. But it means that code such as if (x > vc) vc += a * (vc - x) which assumes a 'perfect' diode, will not be an accurate model of the analog circuit for low values of x. And making it more accurate requires the code to be *much* more complicated. And that's only a simple case. Many real-life analog circuits have several of such 'imperfections' interacting with each other. None of this means that it's impossible to emulate analog audio electronics in software - just that it could be some orders of magnitude more complicated that what one would expect. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
