I'm forwarding this to QA as I think it could require some discussion (see below):

http://bugzilla.audacityteam.org/show_bug.cgi?id=208


Gale Andrews <gale@audacityteam.org> changed:



--- Comment #1 from Gale Andrews <gale@audacityteam.org> 2010-08-19 11:03:49 BST ---
A) Now tested the remaining effects I hadn't, so this seems to be the
definitive list of built-in effects to which the bug applies:

Change Speed/Pitch/Tempo
Equalization
Noise Removal
Nyquist Prompt 
Sliding Time Scale/Pitch Shift

Plus Nyquist process effects are affected, but VST, LADSPA and VAMP plug-ins
are not affected (on basis of those tested).  

B) I've added here a related bug that not all effects that change the timeline
move the control points, which is almost as bad as deleting them. So Change
Speed/Tempo and tempo change in Time Scale/Pitch shift should move the control
points. Reverse should move them (Repeat and Truncate Silence already do). To
the extent that Change Pitch modifies length due to its algorithm, possibly
that should move points too?    

Obviously if it is not practicable to fix B) after A), B) would have to be
split off to a separate bug.

I replied:
(In reply to comment #1)
I'm not sure that, in the case of "Reverse", moving the control points is the
most useful behaviour.

The behaviour that I would "expect", from a user point of view, is that Reverse
would reverse the audio contents and not the envelope. If I want to reverse the
envelope, I would "expect" to need to render the waveform first.

I agree that "not" reversing the control points in the case of Reverse would be
inconsistent and so not strictly "logical", but in many cases it may be more
useful.


Perhaps what we really need is more control of Envelopes.
If there was the ability to cut and paste Envelope Control Points, then it
would make more sense for the Reverse effect to reverse the Control Points as
there would be a simple workaround if that behaviour was not what was wanted.

(Copy Envelope / Reverse / Paste Envelope)
--- end of bugzilla reply ---

The ability to copy and paste Envelopes would be extremely useful in many other situations.
I'm not sure if it currently exists as a "Feature Request", but I expect that may users would love to be able to copy an envelope from one track and paste it onto another track.

Ideally, such behaviour should not be restricted to tracks of the same type - for example it should be possible to copy an envelope from a stereo track and paste it over a mono track. Envelopes are currently all "mono" in that they are just one set of control points, not one set per channel.

While on the subject of Copy/Paste Control Points - it would be a great feature to be able to save/export the control points for use in other projects. Creating a good fade envelope can be very time consuming, and has to be repeated every time. How much better would it be to be able to just export the envelope as a txt/xml file, and then reuse it over and over in other projects?

If the behaviour of Control Points in the case of "Reverse" is going to be changed, then I think that these proposals should be considered now so as to avoid breaking compatibility with current Audacity Projects.


On a second, but strongly related point (possibly even the same point)....
So far we have only discussed Effects.
What about "Generate"?
If you generate a tone into a track that contains Envelope Control Points, should it replace the track, or just replace the audio in the track?
I think the logical answer would be to just change the audio content.

Steve