From an Apple doc on "the Audio Units Community" - Trying Out an Audio Unit Plug-in How can you try out an Audio Unit plug-in to see what it does? One way is to use AU Lab, a free digital mixing application that hosts Audio Unit effects and that ships with the Apple Developer tools. To check out the Audio Unit plug-ins that Apple ships with every system, try the following: 1. Launch the AU Lab application found in: /Developer/Applications/Audio. 2. In the Create New Document dialog, click on the Inputs tab. 3. Click Add Input (click the plus sign). 4. Then select OK. 5. You should end up with a AU Lab document with one input and one output, as shown in Figure 4 (see the righthand column). 6. Play some music or audio through the audio-in jack on your Mac. AU Lab processes the sound. 7. To try an effect, click in the Effects pane and select from the Apple submenu. Try AUMatrixReverb-it should provide a dramatic sound. 8. This effect has a custom user interface that allows you to select multiple bands and then change them as a group, as shown in Figure 5 (below). It also has generic UI, which you can see by selecting Generic View from the upper right control. If you don't provide a custom view for your plug-in, Core Audio can automatically provide a generic view. 9. Try other Apple plug-ins checking to see which have custom UI and which don't. Hope this is found to be useful Aaron