Non-destructive editing

In one of the previous chapters we already discussed that Ardour operates on sessions that encompass all material you have: audio clips, MIDI clips, all effects applied to tracks and busses etc. Before we get to actual editing, let’s talk about basics of non-destructive editing, how it’s implemented in Ardour, and why it should give you peace of mind when you do some heavy editing.

What does non-destructive editing actually mean?

In a nutshell, a non-destructive approach to editing means this: whatever you do, your source material always stays intact. Instead of writing to original files, a program would rather describe changes you applied, store them in a project file, and then “replay” them when loading that project.

How does it work in Ardour?

Here is a quick example. Let’s record a short audio clip, cut it in half and then drag the right half to the right creating a gap:

Here is what actually happens here. Ardour creates a region that references the original audio file and uses all of its data, from the first to the last sample.

When you split the file in two, Ardour creates two regions, and they both reference the original file. But now the project file says: the left region starts at this point in time, begins with the first sample of the original file and stops at that sample in the middle, and the second region starts at a different point in time with that sample in the middle of the original file, and then it stops at the last sample of the original file.

You can cut an audio region into as many smaller clips as you like, move them around tracks, change their start/end points, stretch or contract them etc. The original audio file will never change on the disk.

When you save a project, all that information is preserved in the session file. When you reopen the session, Ardour reads all these references, loads original files and recreates all edited audio regions from original audio files. That’s what “replaying changes” really means.

If you don’t like the way you edited an original take and you are way too far into editing to undo the changes, you can start all over again without recording a new take. For that, you can open the right sidebar by pressing Shift+L, go to the Sources tab, grab the name of the original audio file of the take, drop it on any track and then move it around, cut etc.

Moreover, any effects you apply to a track are also non-destructive. Ardour will apply them to original audio stream and play the result on-the-fly.

In case of MIDI clips played through a synthesizer, Ardour will use the synthesizer to render a stream of audio data while the playhead is rolling, capture that audio stream, apply effects to it, and then play the resulting audio stream as you go.

Differences between audio and MIDI regions

As you already know, audio files are always intact. But MIDI regions are different: you can actually edit their contents, and the changes are saved to MIDI files on the disk.

One case where this matters is when you want to combine multiple regions into one. You can do that with audio regions by selecting the ones you want to merge and them use Region > Edit > Combine. This will create a kind of a meta-region that references N audio files on the disk.

However you cannot do the same with MIDI regions primarily because they are editable on disk, and thus combining something that can physically change can wreak havoc on data continuity.

Where does Ardour store source material?

Consider this generic project. You have here several audio tracks representing drums, two audio tracks for bass and solo guitar, and a MIDI track for electric piano.

If you go to the session folder, you’ll find there a number of subfolders, including these two:

• ‘interchange’, this is where source audio and MIDI files are stored;
• ‘plugins’, here Ardour saves the state of every instance of every plugin used in the project.

When you record one instrument, every take you do is represented by one physical audio file per channel. So if you did three takes in a stereo track, you’ll have 6 audio files.

Does Ardour ever change audio data on disk?

The only time Ardour does anything to actual audio files on the disk is when you explicitely tell you to remove audio files that aren’t used anywhere in the project. Typically this is done when you did dozens of takes, you made your choice and you don’t want these files on the disk anymore because they take space.

Even then, you do it in two steps. First you go to Session > Clean-up > Clean-up Unused Sources to put unused original files into a trash bin, then you separately go to Session > Clean-up > Flush Wastebasket to actually tell Ardour to remove unused files physically.

Continuing

Now that you are familiar with basics of non-destructive editing, let’s do some actual arranging and editing.

Next: Arranging tracks