[QLab] Relative fade strangeness

[Christopher Ashworth]

On Mar 13, 2007, at 9:55 PM, Kevin Faulhaber wrote:

> So I've got a wind cue.  It starts, and then at some point it  
> "swells" in a
> 10 second relative fade up, a 5 second hold, and then a 10 second  
> relative
> fade back down (2 fade cues linked).  When run the first time through,
> everything behaves as normal, however if I leave the sound cue  
> running and
> then run the fade cues again (as in during the rehearsal process)  
> the fade
> up doesn't happen and when the fade down is triggered, the level  
> pops up to
> where it would be as if the fade had happened and then fades down  
> as it
> should.


My first instinct here is to say "this isn't a bug"--because it  
technically isn't, although I know how annoying it is when developers  
tell you that something like this isn't a bug.  ;)

But here's what's happening:

Every fade cue gets its own "knob" on the target sound cue.  Each of  
these relative fade "knobs" are independent.  One fade cue can be  
turning up the volume on its own knob at the exact same time that  
another is turning down the volume.  (This is in contrast with the  
absolute fades: there is only one "knob" for the absolute volume of  
the sound, and when one fade starts to change it, it will take over  
from any other cue that was changing it before.)

Now, what's happening in your case is that when when a relative fade  
finishes, it leaves its allotted volume knob at the final level.  But  
if you restart the fade cue that knob gets reset.  And in your case,  
if you had two relative fades affecting the sound, you are only  
resetting a single one of the relative fade knobs when you restart  
the first fade cue.

There's no way to clear out all the relative fade knobs on a sound  
without restarting the sound.  If you think about it this makes  
sense--it would be awfully weird if stopping a fade cue that wasn't  
running caused the volume of a different sound cue to change. The  
volume knobs "belong" to the sound, and the fade cues just get the  
opportunity to change them.

So when dealing with relative fades, you have to think about the cues  
as having a cumulative effect, and you have to include the starting  
state of the sound in that calculation.  So if you need to recreate  
the exact same sequence, you need to start all the way from the top  
of the sound cue, otherwise you're not resetting all the state of the  
sequence.

Remember that if you need to jump ahead, you can always use the  
playback controls to redo a sequence from a later point in the playback.

Hope that helps,
Let me know if I've muddied up and need to try again.

Chris