Re: Glissando and Portamento

[Stefan Westerfeld <stefan space twc de>]

   Hi!

On Thu, Nov 16, 2006 at 09:56:16AM +0100, Hanno wrote:
> There is one thing thats catching my eye and does not belong into the 
> instruments Im experimenting with. Is there a handling for portamento (more 
> or less fast sliding from one tone to another, thats a midi-effect and has 
> some more parameters like how fast the slide has to be done and so on) and 
> glissando, which is almost the same, but on halvtone-steps like you'll go on 
> a keyboard?

I've experimented with implementing Portamento for monophonic synths.
For those, so the assumption, no change to the framework should be 
necessary, but a module which creates the frequency slide (for those
notes connected by portamento) should be sufficient. My implementation
and my thoughts on after writing it can be found in enhancement
Bug #353137.

   http://bugzilla.gnome.org/show_bug.cgi?id=353137

For non-monophonic synths, the whole idea of portamento doesn't work
well, or at least I don't (yet) understand how exactly it should behave
and be controlled. 

For instance, what should be played for [PianoRoll]

G  ##########

F            #########

E  ##########

D            #########

C  ##########

         \-----/

connected by portamento

Should C slide up into D, or E slide down into D? I don't know exactly
how the midi effect is specified (you said it's a midi effect) - do you
have any references to which midi controller, which settings affect
portamento, and how the above would be resolved?

Of course, if we were to adopt the proposal I made in the enhancement
bug (overlapping notes get connected by portamento), and if we were to
add that cross-portamento (one note sliding up, one down, at the same
time) is impossible, we could fully specify behaviour. That would be:

G  ##########

F            #########

E  ############

D            #########

C  ############

         \-----/

Would mean C slides up into D, E slides up into F, G gets a normal note
off. On the other hand:

G  ############

F            #########

E  ############

D            #########

C  ##########

would mean: G slides down into F, E slides down into D, C gets a normal
note off.

However, this probably only would work with the internal sequencer, as
this way of specifying what slides where relies on the availability of
precise and equal start times for F and D, which - when an external midi
source is used - would always arrive one after the other, but not
necessarily always in the same order.

   Cu... Stefan
-- 
Stefan Westerfeld, Hamburg/Germany, http://space.twc.de/~stefan