OMS WORKSHOP

OMS: What You Need To Know

Published in SOS August 2002
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Technique : Computers

If you're planning to use a Mac for music, you'll probably need to use Opcode's OMS at some time or other. But what is it, and how can you get it up and running quickly?

The Open Music System (OMS) was originally developed by Opcode, and has gone on to become an industry-standard MIDI operating system for all Macs, with the exception of those using Mac OS X. You can think of OMS as a kind of global MIDI driver, overseeing the flow of data between your MIDI instruments, interfaces and software. In this article I'll run through the basics of installing and configuring OMS, and show how you can set up your sequencing software to work properly with it. I'll also look at how you can use OMS to get different applications sending MIDI data back and forth.

The first thing to do is to make sure you have the latest version of OMS installed — v2.3.8 at the time of writing. This may be included with the installation files for your sequencer or MIDI interface, or it can be downloaded free of charge from www.opcode.com/products/oms. Run the installer program by double-clicking on it, and follow the on-screen instructions. After a quick restart, you should be in business. A standard OMS installation consists of the following:
The OMS Applications Folder, usually in an Opcode folder.
The OMS Folder in your System folder.
The Open Music System extension in your Extensions folder.

Note that it is sometimes necessary to reinstall the drivers for your MIDI interface after OMS has been installed for the first time. This is because some driver installation programs will not install all the files necessary for OMS operation if an OMS installation is not detected (for example, some Mark Of The Unicorn USB interfaces can be fussy in this respect). Check your interface manual for details about which drivers need to be present for OMS operation.

The next step is to create your OMS Studio Setup document. This is like a wiring diagram showing how the devices in your studio are connected to one another, and it's what enables OMS to direct MIDI data to and from different instruments and applications as required.

Make sure all your external MIDI devices are properly connected and switched on, then double-click on the OMS Setup icon in the OMS Applications Folder to launch the program. If you're not automatically prompted to create a new Studio Setup, choose New Studio Setup from the File menu, and click OK in the subsequent dialogue box. You'll then be presented with the dialogue box shown in Screen 1, where you can tell OMS which port your MIDI interface is connected to by clicking in the appropriate box. The default options are Modem and Printer, the two standard serial ports found on most older Macs. If your MIDI interface is attached to one of these ports, you can simply tick the appropriate box (or boxes, if you have more than one interface), and click the Search button to continue. However, if you own a Mac with USB ports (for example, a blue and white G3, a G4, or an iMac) then there's a good chance that your MIDI interface will be attached to a USB port instead. In this case you should simply leave both boxes unchecked, and click the Search button to continue.

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After a few moments, you should be presented with something like Screen 2. In this example, four MIDI devices are listed as having been found. The Studio Patches Pgm Chg and IAC Driver devices are both parts of the OMS system itself. The QuickTime Music device is the MIDI driver for the basic virtual sound module built into Apple's QuickTime software. The most important entry in this list, however, is the one labelled FastLane. This is my MIDI interface: a Mark Of The Unicorn FastLane.

If you can't find your MIDI interface in the list, the most likely cause is a missing or corrupted driver, in which case you should exit the OMS Setup program and run the installation program that came with your MIDI interface. If this doesn't fix it, check the manufacturer's web site to see if there is an updated driver available for download. If you're still having problems, check that the cable connecting your MIDI interface to the computer is properly attached at both ends, and not visibly damaged.

Assuming your MIDI interface has been found, you can now click OK and OMS will begin searching for any devices attached to your MIDI interface. After a few moments, a dialogue box something like that shown in Screen 3 should appear. If you're lucky (and if each of your instruments has both its input and output connected to your MIDI interface) OMS may automatically recognise your synths, samplers and so on, and duly display them as named icons in the list. In reality, however, there's a good chance that some or all of your devices will not be automatically recognised and named, and all that will appear are the generic keyboard/question-mark icons shown above. Don't worry, though, because this is not a big problem, and we'll sort it out in a moment.

Each of the keyboard/question-mark icons represents a port on your MIDI interface. Use the check boxes to indicate which of these ports you want OMS to use. Unless you have a specific reason for not doing so, you should tell OMS to use all available ports on the interface. Click the appropriate check boxes, then click OK and you'll be prompted to save the Studio Setup document. It doesn't matter too much where you save it; the OMS Applications Folder is probably as good a place as any. Once you've saved the file, OMS Setup will open a window looking something like Screen 4.

In my case, the Studio Setup document shows two as-yet-unspecified MIDI instruments connected to the FastLane interface. It also indicates that each device is connected to both an input and an output on the interface (hence the arrows pointing in both directions). While this is a perfectly plausible studio configuration, it's not a complete or accurate representation of the instruments connected to my MIDI interface.

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I'm actually using three devices: a Roland PC200 MkII MIDI controller keyboard, a Roland JV1080 multitimbral synth module and an Akai S2000 sampler. Moreover, while the sampler does have both an input and an output connected to the interface (for MIDI sample dumps), the controller keyboard is connected only to an input, and the synth module is connected only to an output. So, in order for my Studio Setup to work properly, I'll need to make one or two changes.

I've decided to use the uppermost of the two keyboard/question-mark icons to represent my controller keyboard, so I'll begin by double-clicking this to open the MIDI Device Info dialogue shown in Screen 5. This dialogue has Manufacturer and Model drop-down menus, which allow me to choose from a list of known devices. In my case I need to select Roland as the Manufacturer and PC200 MkII as the Model from the drop-down menus. For unknown devices, I would just need to enter some basic information in the spaces provided. For instance, is the device a controller? Is it multitimbral? What kinds of data does it send and receive? Which channels does it receive MIDI data on? And what is it called? I can choose to change the icon assigned to a device by double-clicking on the default icon in the top left corner of the dialogue box. This opens a window containing a selection of alternatives to choose from. Clicking OK closes the MIDI Device Info dialogue and returns me to the Studio Setup document.

One final alteration still needs to be made to complete the settings for my controller keyboard. Since the PC200 MKII contains no internal sounds, I never send any MIDI to it at all, so I can disconnect the input that OMS has given it by clicking on the lower arrowhead. A disconnected or unavailable port is greyed out in the Studio Setup document. Note that if an icon appears unconnected to the MIDI interface, dragging and dropping it onto the MIDI interface icon will create the required connections.

Using the procedures described above, I can easily set the remaining keyboard/question-mark icon to represent my sampler. Since this device needs both an input and an output, I don't need to make any alterations to the default connections shown. Now I just need to add a new icon to represent the JV1080. Selecting New Device from the Studio menu opens the MIDI Device Info dialogue, where I can once again choose the Manufacturer and Model from the drop-down menus, and enter any other pertinent information. Clicking OK closes the dialogue, and the new device appears as an icon. By default it will have both an input and an output wired in so, in my case, I'll need to disconnect its output in the wiring diagram by clicking on the arrowhead as before.

The final Studio Setup can be seen in Screen 6. However, it's worth testing it to be sure that it behaves as expected before you settle down to your music making. Selecting Test Studio from the Studio menu puts the OMS Setup application into testing mode.

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If Test Studio appears to be greyed out in the Studio menu, this is probably because you have more than one Studio Setup document on your hard drive, and the one you are trying to test has not been made active. While OMS allows you to create multiple Studio Setup documents, only one can be active, or 'current', at any given time. To make a Studio Setup document current, choose Make Current from the File menu, as shown in Screen 7. A current Studio Setup document will have a diamond symbol beside its name in the title bar of its window, as shown in Screen 8.

In Test Studio mode, the cursor changes into a note symbol, and clicking on any icon representing a device connected to an output on the MIDI interface will cause data to be sent to that device. So, in the example shown, clicking on the Akai S2000 icon should cause the sampler to play a note.

Testing MIDI inputs is similarly straightforward. When a key is pressed on the controller keyboard (or when anything else causes MIDI to be sent from a device to the MIDI interface), the arrowhead for that input will flash, and a voice will say "MIDI received!" via the Mac's speaker.

If you've followed through the steps here, you should hopefully now have OMS up and running well enough to start making music. Now you can get on with the important business of making music, and you'll only need to think about OMS again if your MIDI setup changes.

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