Until recently, Propellerhead Software's ReWire was the only tool for routing audio between Mac software applications. Now three new utilities for Mac OS X offer audio connectivity between applications, and they approach the task in slightly different ways. Each has its merits, and which you choose depends mainly on the audio input and output options available in the applications you want to connect and the complexity of the routings you need.
Soundflower (free) from Cycling '74 provides 2-channel and 16-channel CoreAudio ports that are available to all CoreAudio applications. Audio applications that allow you to choose their CoreAudio output ports can be routed to either of the Soundflower ports. In addition, applications that support multiple output channels can have their outputs routed to individual channels of the 16-channel Soundflower port. That allows you to route individual tracks in Emagic Logic, for example, to the inputs of another audio-recording application, such as Ableton Live. You can use Soundflower with applications that don't allow you to choose their CoreAudio port by selecting the 2-channel Soundflower device as CoreAudio's Default Output in the Audio MIDI Setup application. You can download Soundflower from the Cycling '74 Web site (www.cycling74.com).
Wormhole 1.1 ($25) from Apulsoft is an Audio Units (AU) and VST plug-in that uses TCP/IP to route as many as 100 audio channels between applications that support either of those plug-in formats. Because it uses TCP/IP, it can also be used to route audio between computers. You simply insert one Wormhole plug-in in the source bus of the sending application and another in the target bus of the receiving application. You then select audio channels and enable sending or receiving in both Wormhole control panels. You can use multiple plug-ins to route different signals to different applications or to different buses within the same application. You can buy Wormhole or download a time- and feature-limited demo from the Apulsoft Web site (www.apulsoft.ch).
Jack Tools 0.4 (free) from the Jack OS X Team gives you the best of both worlds: TCP/IP data transfer should be available by the time you read this. Jack Tools provides interconnectivity through a CoreAudio driver called the Jack Audio Server (JAS). You interact with Jack Tools by launching the JackPilot application to activate JAS. Once JAS is running, you use JackPilot's Connections Manager to create audio connections between running applications and to your hardware interface. Like Wormhole, Jack Tools comes with AU and VST plug-ins, allowing you to set up multiple buses between applications or within the same application. That gives you total control in setting up an audio routing matrix, allowing you to use Core-Audio buses as well as AU and VST plug-ins for audio routing. You can download Jack Tools from the Jack OS X Web site (www.jackosx.com).