Crossfade Automation

Special Interest Groups Audio Processing
1

Hi experts…

I supposed this would be easy, but I did not find a comfortable way to do it.

For a kind of “medley”, I have a project with several tacks that already are aligned correctly. Now I want to do a mixdown in a way that at any time only one of the tracks is active. Of course I want to do this is´n a non-destructive so that I can re-edit the cuts.

I hoped that I can easily select a point in time (by moving the play cursor) and have audacity do a mute automation or even better a cross-fade automation to achieve this. Using the Volume Tool separately with each track seems quite a lot of unnecessary work, as you need to take a lot of care to create the two synchronous fades.

Or am I trying to do something in a hard way that can be achieved easily with other methods ?

Any tips ?

Thanks,
-Michael

2

Use the “Envelope” tool?

3

This is what I did (erroneously calling it “Volume Tool” in my post).

But (as far as I see right now) same only “sees” a single track at a time and thus doing a (very fast) crossfade between tracks without creating holes or double-amplitude areas seems a lot of work. I hoped for a tool that e.g. would do a constant-sum-amplitude cossfade between two tracks within a selected area of time.

What am I misssing ?

-Michael

4

I agree that making cross-fades is unnecessarily fiddly. (compare with how easy in Cool Edit Pro).
I think there is a feature request for an improvement to this, so I presume that you would like your vote adding to it?

5

Yep. How to do that ?

-Michael

6

I’ve moved this topic into the “feature request” section of the forum.

This is the current entry on the featur request page of the Audacity wiki http://audacityteam.org/wiki/index.php?title=Feature_Requests

Envelope Tool:

  • When setting control points, have in Status Bar or tooltip the gain amount and position in the timeline. (2 votes)
  • separate mouse click e.g. ALT + click for adding control point without adjusting envelope. At the moment, clicking adds a control point and drags. If you are far from a control point and want to tweak the envelope, but don’t want to add a new control point, you need to go back to the control point. (1 vote)
  • Linear envelope editing When using the envelope tool, the applied fades are concave curves (logarithmic fades?). If I want to make a linear fade using the envelope tool, I need to create multiple small fades to create an envelope that approximates to a straight line. I think that it would be a useful feature if Audacity could apply different shaped envelopes, perhaps using “Shift” + drag for linear envelopes and “Ctrl” + drag for inverse envelopes.
  • Better control for Envelopes:
    o Hold down CTRL button and click on Envelope creates a control point but doesn’t alter the envelope (it currently starts dragging the envelope straight away which isn’t very helpful)
    o Hold down ALT key and drag between two envelope points to move only that section up or down (the two above points are handy for changing the volume of a section of audio without having to drag individual points around).
    o Modifier keys to select moving the envelope point in either the horizontal or the

There are a number of ideas here, and probably this could do with some rewriting, but the general gist is that the envelope tool is currently not very user friendly.

I personally think that being able to add a control point without automatically changing the envelope, and for the envelope to extrapolate in a linear fashion between the control points (a straight line between control points when on the default track display) would help enormously. This would not produce am exact “equal power” cross fade, but it would be much closer than the current implementation, and in most cases would be close enough. It would also make it very much easier to create a gradual fade out to silence.

“Waxcylinder” (one of the forum moderators) generally handles transfering “feature request” ideas from the forum to the wiki. He does this when the forum topic has been inactive for a month (so as to give everyone an opportunity to discuss the issue). So here is an opportunity to have your say…

7

I feel that the suggestions for improving the way to do envelope definitions are quite independent from what I would need for crossfading. So I thinks this (handling two tracks with one action) is an additional feature.

For me (as an audacity newbie) an easy and quite versatile way to get what I need would be this:

Creating a crossfade:

  • select a range in time with the usual means
  • select two of the tracks (a crude way would be using just two unmuted tracks, leaving alone the others)
  • one of the tracks (1) should show 0% envelope left of the selection, the other (2) should show 100% envelope there
  • The “crossfade” action now generates 100% envelope right of the selection for track (1) and 0 % envelope for track (2), with linear envelope interpolation within the selection.

There should be a way to edit the cossfade aera (stretch and move):

  • select two tracks and an area of time that contains exactly one complete crossfade location created with the crossfade tool
    -action “fined crossfade”: The selection automatically shrinks to the edges of the cossfading area created previously. Same is is found according to the envelope curves of the two tracks (error condition if no plausible cossfade area is found).
  • now you can move and stretch the selection with the mouse (best showing the envelop curves accordingly).
  • action: “fix crossfade” defines the new level curves.

Downside: When using this type of crossfading, you can’t use the “envelope” feature for other stuff in this project.

What do you think ?
-Michael

P.S.: If possible the thread should be renamed to “Crossfade Automation” (I had been typing faster than thinking…)

8

Possibly not.
This is the kind of thing that I had in mind - I think that this would satisfy, or at least come close to your requirements, while at the same time would greatly simplify other types of envelope manipulation.

In the picture below I have two tracks, each containing some audio. I have used the “Time Shift Tool” to adjust the positions of the two audio clips so that they overlap. The overlapping region is where I want to apply the cross fade, so I have used the Selection tool to drag across the tracks and make my selection.
selected-region.png
The next step would be to select “Cross-fade” from the effects menu, that would automatically create the necessary envelope points to create a cross-fade.

In this next picture we see a cross-fade (I had to create this manually by adding loads of control points, which is quite time consuming, but what I think we would both like is for this effect to be achieved with a single click).
equal-power.png
An additional problem (as well as being time consuming creating all of the dots), is that if we want to adjust this cross-fade (for example, to make the overlap greater and have a longer cross-fade it is necessary to adjust every control point - in effect, completely remake the cross-fade.

Now let us consider if the amplitude envelope used straight lines.
Starting with our overlapping audio clips as shown in fig. 1. we apply a cross-fade.
My proposal is that it would create something like this:
cross-fade.png
OK, so it isn’t an equal-power cross-fade, but in most situations it is close enough for the difference to be barely audible. (Also, the manual addition of a single control point to each track could easily and quickly be applied to “pull the envelope a little wider” if a closer approximation is required).

More importantly, the fade can be very easily adjusted manually as there are only two control points for each track (the start and the end points).

This would also be achieved. Since the cross-fade is only creating two control points per track (the start at 1.0 and the end at 0.0), adjusting the track positions with the Time Shift tool and applying the cross-fade effect again will effectively overwrite the previous cross-fade. (lots more pictures would explain this better, but I think that you probably get the idea without).

When the cross-fade effect is first applied there should probably be a (dismissable) pop-up to warn that any envelope control points within the selected area will be deleted.

With the above method, envelope points in regions outside of the cross-fade area would not be affected.
The control points created by the cross-fade effect would just be ordinary control points like any other.

9

I suppose your suggestion easily can be extended to not needing to use the start of a track as the starting point of a crossfade. For me this would be essential.

But anyway I’d like to see a method that works on (at least) two tracks (to be “crossfaded”) at the same time. Here defining a crossfade “start” and “end” point and editing these points should be easy to do. Maybe this can be implemented on top of what you describe.

OTOH I can imagine a completely different tool:

Some kind of “fader automation track” (similar to or integrated with the time track) could be introduced.
In this track, you can define “fader automation points in time”. Each of these points defines a “fader position” (in dB, lower or equal zero) for one or more of the audio tracks. Once defined, these points can be moved in time with the usual means; for each, of course, the tracks’ fader level definitions can be modified, added and deleted (deleting the last track-fader-level definition deletes the “point”).

The “fader automation” for each track can be used additional and independently of the “envelope”.

On playback, for each track, the “automated fader position” is interpolated (linearly in dB) between the points containing definitions for that track and the result is added (in dB thus multiplied) with the current “envelope” value and used to define the playback volume.

This is not based on anything already implemented, but IMHO this would be a really cool and very intuitively usable feature !

What do you think ?

-Michael

10

That is essentially what the “envelope” does, with the exception that the envelope only acts on the track to which it is applied. In effect you are describing a second level envelope that “envelopes the envelopes”.

A recent development in Audacity is the “Link tracks” feature. Personally I think this feature requires some development and refinement as it is at times rather confusing, and still seems to have a few bugs in it (some of which have now been fixed in the 1.3.8 alpha version).

Perhaps at some time in the future it will be possible to link envelopes in tracks, and in this way achieve what you are describing (a “dummy” track with no audio, but just an envelope could be linked to other tracks, so that the envelope of the dummy track is applied to the audio tracks to which it is linked).

For the short to medium term, I would be happy to see improvements to the current features (envelopes and track linking) to make them more easily usable and bug free.

11

The “envelope” handling is rather complex, as it can be used for much more complex things than simple “cossfading”. Of course improving the envelope tool to be easier to use is a good idea and if this results in an easy to use crossfade tool (by linking traks in some way) this might be a goos solution.

OTOH I feel that the “fader automation track” or something similar is especially intuitively usable for crossfading and some other tasks (e.g. parallel fading out of multiple tracks).

-Michael

12

Now that the requesite month has expired I have moved the gist of this FR to the Wiki Pending Feature requests page for triage by the developers. I have left this thread in the forum, but moved it to Audio Processing as it contains some useful information. I have provided a link back to this thread from the Wiki Pending FRs.

WC

13

This is our idea of what automatic cross-fade would be like when joining two clips on one track. Something as “one step” as this is I think what Michael is asking for and will be a new request on the Feature Requests page. I’ll add some votes from other people who have asked for this via other channels too.

I assume this also works in principle when the tracks are underneath each other. Regions are not explicitly selected, so I don’t know if you can carry on pushing tracks into each other to simulate different lengths of overlap. Although this is unlikely to be developed before the next Stable release, you could subscribe to our developers’ mailing list if you wished and discuss how this might be implemented in more detail.

I think the envelope enhancements are a more specific request as they won’t give a one step fade. We already have requests e-mailed to us for a “master envelope” or “fader track” so I’ll add Michael’s vote to those votes.


Gale