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.

(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)

> Extra comment by Steve Aug 19, 2010:  
> 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.
> Stereo track have 2 envelopes - one for each channel, so although it may 
> make sense to allow a mono track envelope to be applied to a stereo track, 
> copying a stereo track envelope to a mono track would be more problematic.
I think "replace" is probably better (correctable with pasted envelope points if needed).

(In reply to comment #3)
If audio and envelope points are conceptually different "layers", I don't see the logic in removing the envelope points if audio is generated or pasted into a track.

Why would a user generate audio into a track that has envelope points unless they wanted to use the envelope points? If they don't want the envelope to apply to the newly generated audio then the logical thing would be to either, not generate audio into that track, or delete the envelope points either before or after generating the audio.

There are potentially "conceptual" problems when considering all of the combinations of cutting, pasting, deleting, generating, splitting and reversing audio with/without control points. Currently I think Audacity sometimes does "the wrong thing" (as in the case of this bug report) and in that sense it is a bug, but I think that resolving the issue will require a reworking of the whole concept of what envelopes are and how they should behave. In which case it's probably better to describe it as a new feature for future development (post 2.0).

Perhaps this bug report should be closed as "can't fix" for now, and the issue transferred to a New Feature Proposal on the wiki. (I thought there were some posts on -devel regarding handling other types of "controller tracks", but I can't find them now).

(In reply to comment #4)
> Why would a user generate audio into a track that has envelope points
> unless they wanted to use the envelope points?
Well maybe I'm zany but I usually regard "generate" as new audio. If I generate at 0.8 that's what I would want, not to have the amplitude fitted to existing control points. 

I don't think the bug should be "wontfix" as the behaviour that some effects remove control points but not others is unexpected (e.g. Bass Boost retains the control points but EQ removes them). Making behaviour consistent may not necessarily require a rework of envelopes. 

Cut and paste of control points would seem to be handy anyway, but if you look on Wiki Feature Requests there are suggestions at least for an "Effect Track" (http://wiki.audacityteam.org/wiki/Feature_Requests#New.2FModified_other_GUI_elements) and "Panning Envelope". 

I'm fine with a WIki Proposal Page for new control tracks (also considering whether new control tracks and enforcing consistent envelope behaviour would require a rework of envelopes). You could link there to this bug but I don't think it should be closed.

Confirmed that this still happens with Noise Reduction (the rewrite of Noise Removal)

*** STEPS UPDATED ***

Testing on W10 with 2.3.2 RC001

This is still the case - I made minor changes to the bug report

Tested on W10 with audacity-2.3.3-alpha-326-c9fbd283b7bfc8702caf86a4672cba7ff6260b7d

This has propagated to the new for 2.3.3 Filter Curve  and Graphic EQ (sliders) effects, similarly afflicting them.

Envelope control points werte removed by both new effects

I think this deserves a P2 (marginal P1) as it potentially irrevocably changes/destroys a users audio data.

This had long-languished as our oldest P3 - it's about time we fixed it.

Bug #1686 appears to be a duplicate of this bub

This is out oldest P2 bug by far - and it really is something we should be fixing

See that latest user report on the Forum:
https://forum.audacityteam.org/viewtopic.php?f=46&t=111560

Upping this to P1 as it can cause users to damage their project data.

*** STEPS UPDATED ***

Steps updated to be explicit about the affected effects.

At least I think I got it right... :-)

https://github.com/audacity/audacity/commit/c13a074

(In reply to Leland Lucius from comment #16)
>At least I think I got it right... :-)

Looks to me that you got it right Leland   ;-)

Testing on W10 with Audacity 3.0.0 58adb94

I tested with all those effects listed in the steps and none of them remove the envelope.

(In reply to Leland Lucius from comment #16)

Testing on macOs 10.15.6 Catalina with Audacity 3.0.0 58adb94

I tested with all those effects listed in the steps and none of them remove the envelope.

Works for me on Linux.