ReWire

If you’re using only one music program, the transport should operate in a smooth, transparent way: Click on a button, and it does what you expect. But what if you want to run two music programs at the same time, in the same computer? If you try to click on the start button in one program, then switch to the other program and click on its start button, the best you can expect is a train wreck. The tracks from one program will be hopelessly out of sync with the tracks in the other.

The technology that solves this problem is called ReWire. ReWire was first developed by Propellerhead Software. They wanted their Reason program to be able to operate in tandem with sequencers such as Steinberg Cubase and Apple Logic. Reason is very good at some types of music recording, but can’t be used for other things: It has no audio tracks, for instance, so you can’t record vocals into it. Propellerhead needed a way to let their users create instrumental tracks in Reason and then do vocal overdubs or other types of tracks in a general-purpose sequencer.

The ReWire idea proved so useful that it has been included in many other music programs. Using ReWire, you can link Cubase with Ableton Live or Image-Line FL Studio with Digidesign Pro Tools, for instance. ReWire is strictly for two programs running in the same computer, though: There’s no way to use it to link two pieces of hardware.

USING REWIRE

When you’re finished doing whatever music work you want to do, you’ll need to quit the client first, then quit the host. If you try to quit the host while the client is still running, an alert box will let you know you’re trying to do things in the wrong order.

ReWire provides several links between the host and the client:

• You can use the transport buttons in either program. The other program will respond just as if its own transport buttons had been clicked. (Generally, the Record button will only start recording in the program that you’re currently looking at, not in the other program.)
• The tempos of the two programs will be linked. If you change the tempo in one, the other will change to match.
• The song position will always be the same. For instance, if you use a Locate marker to set the song position to bar 29 in one program, the other will also locate to bar 29. And during playback, the two programs will never drift out of sync.
• If you set a playback region to loop in one program, which is often useful while you’re developing a song, the other program will loop too. Its loop start and end markers will have the same settings, and its loop on/off button will have been clicked.
• The audio outputs from the client will appear in the mixer of the host, as shown in Figure 2. (In some hosts, you may need to activate the ReWire inputs before this will happen.) The host mixer then produces a complete mix of its own tracks and the signals coming from the ReWire client. This mix is what you hear at the computer’s audio outputs; the client never sends signals directly to the audio output.
• MIDI data from the host can be directed to the client.

REWIRE & MIDI

One important difference between a ReWire client and a plug-in is that the parameters of a plug-in can usually be automated in the host. To automate parameters in a ReWire client, you need to assign the parameters to MIDI Control Change messages, which will be recorded into the host’s MIDI tracks. In a future column I’ll have much more to say about automation.