Add a section on non-destructive editing

content/editing-sessions/arranging-tracks/index.en.md

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 title = "Arranging tracks"
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content/editing-sessions/non-destructive-editing/index.en.md

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+title = "What is non-destructive editing?"
+description = "What is non-destructive editing and how does it work in Ardour?"
+chapter = false
+weight = 1
+#pre = "<b>1. </b>"
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+
+In the previous chapter 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:
+
+{{< figure src="en/non-destructive-editing-cut-move-example.gif" alt="Cutting and moving a audio region" >}}
+
+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.
+
+{{< figure src="en/non-destructive-editing-redo-all-over-again.gif" alt="Redo the editing all over again" >}}
+
+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.
+
+{{< figure src="en/session-example.png" alt="PLACEHOLDER SCREENSHOT" >}}
+
+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: [Importing audio](../importing-audio)
+
+
+<!-- ## Is it Ardours-specific?
+
+Not really. It's a very popular you'll see in pretty much every digital audio workstation, non-linear video editor and even advanced image editors. The idea is the same, implementation varies from program to program.
+ -->