197 lines
9.2 KiB
Plaintext
197 lines
9.2 KiB
Plaintext
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MIDI INTERFACES FOR THE IBM PC
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by David (Rudy) Trubitt
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from September, 1990 issue of ELECTRONIC MUSICIAN
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If you are looking for a MIDI interface for an IBM PC or
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compatible system, don't consider it a simple hardware purchase.
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The interface you use will have a big impact on the software you
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will be able to run. Unlike the Macintosh or Atari ST, there is no
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serial communication driver built into the PC's operating system.
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For that reason, interfaces and software are not automatically
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compatible. But there is a de facto standard: Roland's MIDI
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Processing Unit (MPU-401).
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When it was introduced in 1984n the principal selling point of
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the MPU-401 was Intelligent mode, which takes care of many
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important MIDI talks without bogging down the PC's central
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processor. The IBM PC's of 1984 had less poser than today's
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models, so the MPU's processing capabilities were useful. Roland
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offered the MPU-401 chips to other companies, making it easy for
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them to make compatible products of their own. Enough MPU-styled
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interfaces were sold that nearly every software company had to
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support it to stay competitive. This is still the case. Even
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programs designed specifically for non-MPU interfaces usually offer
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MPU-compatible versions.
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The MPU-401's biggest advantage today is software
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compatibility. If you want to run the largest number of programs,
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especially shareware, you should be looking at an MPU-compatible
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interface.
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Today, the typical PC-compatible has increased in power to the
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point that it doesn't need the help Intelligent mode offers. Also,
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Roland's MPU-401 chips discard MIDI time code (MTC) messages when
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in Intelligent mode. As an alternative, the MPU can operate in -
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you guessed it - Dumb mode (also called UART mode), which does pass
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MTC messages. In this case, the computer is responsible for
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everything and all features of Intelligent mode are lost. Many
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developers who support the MPU-401 today are using Dumb mode,
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despite the extra work it entails. This means that users pay for
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unused features.
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Several manufacturers have taken the basic MPU-401 and added
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additional MIDI ports and SMPTE read/write capability. (for you
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non-musical types out there, SMPTE is a time code used mainly in
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multi-track recording and audio-video sync-ing...LC). These
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interfaces function like a plain MPU0401 unless the software is
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specifically written or updated to support the additional features.
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Check with the software manufacturer to find out if their software
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supports any "extras" that your interface provides.
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NON-MPU INTERFACES
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MPU-401 compatible interfaces must be installed in an
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expansion slot, forcing laptop users to seek alternatives. Many
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laptops use a MIDI interface that works with the printer port,
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either serial or parallel. You'll have to call your software
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vendor to find out if their programs support these interfaces, as
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none of the serial or parallel interfaces are MPU-compatible.
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To achieve the MIDI rate of 31.25 kilobaud (and you guys
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thought your modems were hot stuff!!!!!.....LC) serial MIDI
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interfaces run the PC's serial port at higher rates than were
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originally intended. In most cases, this is no problem, although
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one software vendor cited potential throughput problems in dense
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datastreams. There are a number of serial interfaces available,
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and they are gaining support among software vendors.
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The parallel port has some potential advantages over the
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serial port as a host to a MIDI interface. Suprisingly, there is
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only one parallel port MIDI interface on the market today, the
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Eclipse HRS-3000.
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BUILT-IN SOUND AND PREPACKAGED SYSTEMS
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Several manufacturers make cards that incorporate interfaces
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with onboard synthesizers, which are well-suited for educational
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applications. Game software can also take advantage of this type of
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device for generating sound effects and music that are synchronized
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with the on-screen action.
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Some systems of this type, such as the IBM PC Music Feature
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Card (which includes an onboard Yamaha FB-01 synth), are not MPU-
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compatible. Roland's LAPC card on the other hand, combines an MPU
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interface with a Roland MT-32 synth. In some cases, the MIDI
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implementation of game-oriented boards may be limited, so read the
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fine print.
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Most MIDI interfaces include some of tape sync capability as
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part of their design. However, in nearly every case, the signals
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that they put on tape are incompatible with each other (with the
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exception of the four different frame rates of SMPTE).
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WHO'S DRIVING THIS THING ANYWAY?
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To transmit and receive MIDI messages, a special software
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program called a device driver is used. The application program
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communicates with the driver program rather than with the interface
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itself. Typically, a device driver is designed into each
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application program, and drivers are incompatible from program to
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program.
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To acheive the blissful state of INDEPENDENCE, in which the
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user selects software and hardware without concern for
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compatibility, a system-wide driver must be written to support a
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number of interfaces and programmers must agree to support the
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protocols used by that driver. Such a driver can also be designed
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to manage access from several programs simultaneously in a
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multitasking environment, such as Microsoft Windows 3.0.
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Playroom Software is close to releasing its MIDI Executive
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program, a driver for several popular interfaces that can also
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manage more than one interface and application simultaneously.
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Playroom is encouraging other software vendors to support MIDI
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Executive but MIDI Executive requires the Windows environment, and
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most current PC users are using DOS wothout Windows. Also, it is
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almost certain that Microsoft will offer some sort of MIDI support
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in fuuture versions. Although Microsoft's offering may be less
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sophisticated than Playroom's there is a possibility that the two
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will compete for developer support. A solution like Playroom's
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could be a real step forward for MIDI on the IBM PC.
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In summary, let your software needs drive your hardware
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purchase. If you aren't sure of your future needs, an MPU-401
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compatible interface is a safe choice. If you are putting together
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a system primarily t run one package, ask the software vendor for
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a recommendation.
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MANUFACTURERS OF IBM PC MIDI INTERFACES
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-Brown-Wagh Publishing: (408) 395-3838
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-Computer Music Supply: (800) 322-MIDI or (714) 594-5051
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-Eclipse: (800) 456-6434 or (214) 238-9944
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-Kee Electronic Enterprises: (800) KEE-MIDI ext 10,
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or (817) 560-1912
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-Mix Bookshelf (IBM PC Music Feature) (800) 233-9604
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or (415) 653-3307
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-Music Quest: (800) 876-1376 or (214) 881-7408
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-Optronics Technologies (503) 488-5040
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-Passport Designs: (415) 726-0280
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-RolandCorp US: (213) 685-5141
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-Voyetra (800) 233-9377 or (914) 738-4500
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David (Ruby) Trubitt would consider a MIDI brain implant if it were
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MPU-401 Compatible.
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SIDEBAR 1
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IRQ's - NINETY PERCENT OF THE PROBLEM
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If you're having a problem installing an interface card in
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your PC, your MIDI interface and some other card may both be trying
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to use the same interrupt request line or IRQ.
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IRQ's are a way for parts of your PC (such as a MIDI
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interface) to tell the CPU to stop what it's doing and take care of
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something that can't wait (such as reading incoming MIDI messages).
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This request is made by toggling the state of a pin on the
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expansion bus. If two cards are trying to toggle the same pin, the
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CPU may lock up. MPU-401 Interfaces normally are shipped using
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IRQ2.
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Other plug-in devices also may be set to IRQ2, and some
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Leading Edge and Tandy 1000's use IRQ2 for disk controlor other
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functions. If the offending card cannot be removed to have its IRQ
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number changed, you'll have to change the IRQ settings on the MIDI
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interface. Most newer interfaces have user-selectable IRQ's, but
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your software must be able to use the alternate IRQ or it won't
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recognize the presence of the interface. Many new programs offer
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user-selectable IRQ's, but older programs and shareware may not
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have this ability.
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SIDEBAR 2
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There is a chart which I scanned in very hurriedly as .PCX file.
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You are welcome to view it, but it is hard to read. This is all
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from the September issue of Electronic Musician, a great magazine
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if you are into computer/music interaction.
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The following text is a postscript to the chart (which is
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MIDI1.PCX, MIDI2.PCX and MIDI3.pcx)
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"Sound" refers to onboard synthesis capabilities ( a metronome
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doesn't qualify). "MPU" refers to MPU-401 Compatibility.
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1 Soundblaster cannot use MIDI ina and out simultaneously
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2 CMS-444-EXB Expansion rack adds four MIDI ins, four outs, and LED
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monitor; $279. Extra I/O not MPU-401 compatible.
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3 Can upgrade to 1-in, 4-out CMS-404 for $39.
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4 The two MIDI outs are independent, providing 32 channels
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5 With optional Quad Pask, foutr non-independent MIDI outputs
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provided.
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6 Supports Pre-MIDI, 5 volt clock sync and converts to/from FSK and
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MIDI clock.
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7 Same model works with Atari ST and Amiga
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8 HRS-300 must select one of three inputs, non-merging. Same signal
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sent to all three inputs.
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9 Price for package that includes interface, sequencing software,
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cables, and videotape.
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