ۥ-x@ -?zG>F$F$$F$F$F$F$F2FFFFFF FFF(GGGGGGGGGGGGGGG$G4XG"$G$F$G$G !PC/MIDI BASICS #2: MIDI INTERFACES by Richard D. Clark (PCC RichC) 11/19/91 (updated 5/6/92) A MIDI device is anything with MIDI connectors that can perform an action in response to an incoming MIDI data stream, and/or transmit such data. Common MIDI devices are synthesizers, tone modules, samplers, effects devices, drum machines, stand-alone sequencers, lighting controllers... and computers. Most computers, especially IBM-compatible PC's, are not equipped with MIDI connectors as standard equipment; they must be added, in the form of a "MIDI Interface." Once equipped with an interface and suitable software, a PC can become the "command center" of a music composition and performance system whose complexity and capabilities are limited only by the needs and resources of the user. MIDI interfaces produce no sound of their own (although some "music cards," which DO have sound-generating capabilities, include MIDI interfaces). They simply act as interpreters between PC's and external MIDI devices. Audio connections are made between the external devices and a playback system. _____TYPES OF MIDI INTERFACES *Roland MPU-401 (and Compatibles) The Roland MPU-401 was the first MIDI interface designed for the IBM-PC and compatibles. It consisted of two parts: the MPU-IPC, an 8-bit Input/Output card installed in an expansion slot of the computer, and the MPU-401 MIDI Interface itself, which was an external box connected to the IPC via a serial cable. The MPU-401 box was also used, with a suitable card, for Apple and Commodore computers. The MPU-401 is an "intelligent" interface, which takes over the processing of MIDI data, removing that burden from the computer's CPU -- a necessity in the days of the 4.77MHz IBM-PC. It supports one MIDI In and one MIDI Out (it has two Out jacks, but the same data appears at both); includes an internal metronome (software controlled), and FSK (Frequency-Shift Keying) tape synchronization (more on tape sync below). The MPU-401 has become the "standard" MIDI interface; virtually all MIDI software for the PC supports it. Thus, it's no surprise that the MPU-401 has been widely cloned. Some interfaces -- notably those manufactured by Voyetra -- achieve MPU compatibility by using a genuine Roland chipset; most others are "clones." However, very few reports of compatibility problems have arisen from any of the major manufacturers' interfaces. At this writing, MPU-401-compatible interfaces are available from a number of manufacturers, including: CMS (401-II, $129; 444-II, $249; and 444-EX, $399); Music Quest (PC MIDI Card, $129; MQX-16, $199; MQX-16S, $249); Roland (MPU-401, Super MPU, list prices unknown); Voyetra (V4000, $139; V-22m, $219; V-24sm, $389). (Note: all prices in this article are manufacturer's list; discounts are common.) These are the most widely-used and supported interfaces; others may be available from other manufacturers as well. The differences in prices arise from the presence or absence of "extra" features beyond basic MPU-401 functions (16 channels ofMIDI I/O). These features are discussed below. *"Music Cards" The Sound Blaster, Sound Blaster Pro, ProAudio Spectrum and the possibly forthcoming AdLib Gold are among the PC expansion cards that include, among many other features, a MIDI interface (optional on the Sound Blaster). These interfaces support full-duplex (simultaneous MIDI In and Out) operation, but offer few or no other MIDI features. (Note that full-duplex MIDI was added to the Sound Blaster with the recent Version 2.0; earlier versions did not support simultaneous in/out, severely limiting their usefulness as MIDI interfaces.) The MIDI interfaces included with these cards are not MPU-401 compatible. Be warned that manufacturers of some "clone" music cards advertise that their interfaces are "MPU compatible," but in small type (if at all) add "in UART mode." The MPU-401 can be run in a mode that bypasses its onboard processor, and this is the mode they're talking about. Software that "requires an MPU-401 or compatible" will probably *not* work with these interfaces (which are the same as the Blaster-type interface). The utility of these interfaces is somewhat limited by the software available to support them, but this is less true than it was in 1991. All are bundled with a basic MIDI sequencer (an entry-level version of Voyetra's Sequencer Plus in the case of the SB's and the Spectrum). Support for the SB/MIDI-type interface is growing, especially with the introduction of Multi-media support in Windows 3.1. Any MIDI program designed to work with Win3.1 or later will support these music cards' MIDI interfaces. Still, many older MIDI programs, and those not designed for Windows -- editor/librarians, sequencers, notation programs, etc. -- do not yet support FM card MIDI interfaces. These cards can be a very cost-effective entry to the world of PC music and MIDI. Their on-board synthesizers can be used as additional tone modules in a MIDI system; they can provide great sound for games that support them; they include DAC (Digital/Analog Converter) circuitry that provides digital recording and playback capability (not accessible via MIDI, unfortunately); and some even include joystick ports and SCSI connectors for CD-ROM drives. *Serial Interfaces Serial MIDI interfaces connect to the PC's RS-232 serial port, and thus do not require an expansion slot. Such interfaces are the only practical choice for use with portable computers that have no expansion bus. They are not widely supported by MIDI software, although Twelve-Tone Systems' Cakewalk and Cakewalk Professional (character-based sequencers) do support them, making the combination very usable in a portable computing environment. These interfaces are manufactured by Key Electronics (MS-101 Midiator, $119; MS-103 Midiator, $179; MS-114 Midiator, $229.) Key has recently introduced multiple-MIDI-port versions of the MIDIator, and a version that works with a parallel port. And one sequencing/notation package, Music Printer Plus, now supports the MIDIator interface. *Multiple-Port Interfaces The MPU-401 standard is limited to one set of 16 MIDI channels. As MIDI systems became more complex, and the use of multi-timbral synthesizers became widespread, 16 channels became an unusably small number for many systems. Additional channels are implemented by creating "ports;" each port transmits its own set of 16 MIDI channels. By definition, multi-port interfaces are not MPU-401 compatible. However, they can be made so. Music Quest, for example, sets up their multi-port 444 series interfaces so that one input and one output can function as an MPU-401. Voyetra's V24sm includes an MPU "daughterboard" that can be addressed as an MPU "port" by software. Also, more than one MIDI interface can co-exist in the same PC; a multi-port interface can be installed along with an MPU; their outputs can then be routed to a MIDI "thru box," which can switch the external MIDI system to accept output from either interface. Of the interfaces listed above, the CMS 444 series and the Voyetra V-24sm are multiple-port interfaces (which include MPU compatibility). Others are the Music Quest MQX-32M ($349) and the Voyetra V-22 ($129) and V-24s ($299). The new Roland Super MPU offers 32 MPU-compatible MIDI channels plus SMPTE. _____MIDI INTERFACE FEATURES *Inputs/Outputs All interfaces provide a minimum of one MIDI In and one MIDI Out/Thru connector; many provide two or more outs, which operate in parallel (the same data appearing at each output). This can allow you to connect several MIDI devices to the interface without "daisy-chaining," with the potential for audible time delay that can be introduced by some devices that "hold on" to MIDI data for a split second before passing it to their Thru ports. However, "Thru Boxes" are relatively inexpensive, and can easily be added later as your MIDI system grows. It's important to remember the distinction between an interface with multiple parallel outs (all being used by one MIDI data stream of 16 channels), and one with multiple ports (each addressed by a separate stream of 16 channels each). *Tape Synchronization Tape sync is one of the least-understood and most under-used capabilities of many MIDI interfaces. Tape sync (using FSK) was included in the original Roland MPU-401, but most entry-level compatibles omit this feature. Tape sync is a very useful thing. In advanced MIDI systems, it can be used in film and video post-production (allowing exact placement of sound-effects and music cues), as well as for the creation of "virtual tracks," controlled by the sequencer, that are synchronized with analog tracks recorded on a multi-track tape deck. These techniques can be used in a home system too, and if you have access to a four-track "portable studio," I highly recommend that you purchase a MIDI interface with tape sync capabilities. The technique is simple: 1) Create a sequence that contains the same number of measures and the same tempo changes as the final song; 2) Connect the interface's "tape out" to an input of the multitrack (usually an "outside" track, 1 or 4 on a four-track); 3) Issue the appropriate sequencer commands to generate "sync tone" or "time code," put the deck into record, and while playing the sequence record the sync tone or code on the deck (this is referred to as "striping the tape"). You can also place a "scratch mix" of your sequence on a different track at the same time. 4) Rewind the tape, and connect the line out of the sync track to the "tape in" of the interface. Tell your sequencer to "sync to external time code," and play the tape. The sequencer will read the sync from the tape, start playing, and remain "locked" to the tape through the sequence. Tape sync comes in different varieties, with different capabilities. The simplest is FSK (Frequency-Shift Keying), wherein the interface generates an audible signal consisting of two frequencies (1.25kHz and 2.5kHz in the case of Roland FSK) alternating at a rate determined by the tempo of the sequence. The primary disadvantage of FSK is that there is no "location" information (except for "start") in the code, so in order to sync to tape you must always start the tape and the sequence from the beginning. Time Code avoids this problem by including data marking the progress of time in detail as the code is generated and recorded. SMPTE Time code (a standard developed by the Society of Motion Picture and Television Engineers, hence the acronym) is the mostcommonly used; it generates time code divided into hours, minutes, seconds, and frames (the frame rate can vary depending on the application). When a tape is striped with SMPTE Time Code, a properly-equipped sequencer/interface can read an exact location from any point on the tape, and within a second or two "chase-lock" the sequencer playback to that point on the tape. Other "smart" sync systems exist, utilizing MIDI Time Code, "Smart FSK" and other systems. However, the cost of MIDI interfaces that can read and generate true SMPTE Time code has dropped in the last year to a point so low that there's little reason to use anything else. Interfaces that offer SMPTE capabilities include: Voyetra V-24s ($299) and V-24sm ($389 with MPU compatibility); CMS 444-II ($249) and 444EX ($399), both with one MPU-compatible port; Music Quest MQX-16s ($249, with MPU compatibility) and MQX-32m ($349); and Roland's new Super-MPU with 2 MPU-compatible ports (price unavailable). Tape sync can be used, even with a standard home cassette deck and "dumb" FSK, to effectively double the polyphony and voice capabilities of your MIDI system. Here's how: 1) Create a sequence that includes as many parts as you want. Record the sync tone on the left channel of a cassette, and a mix of the sequence on the right channel. 2) Mute as many tracks in the sequence as necessary to free up synth voices while still having reference tracks to play to. 3) Add new tracks -- new parts, new voices doubling old parts, whatever. 4) Mute all the "old" tracks in the sequence. Connect the right channel output of your tape deck to your mixer or audio amp along with the audio output of your synth(s). Rewind the tape, put your sequencer in external sync mode, and start the tape. You'll hear the original parts, as recorded on the tape, play back in sync with the new parts being played by the sequencer. As long as you don't change the structure of the song, you can even go back and change the original parts (while muting the new ones) and re- record the tape (replacing both audio and stripe). *Metronome The original Roland MPU-401 included an internal metronome which "beeped" in time to the tempo generated by the sequencer. Other interfaces can generate this beep through the PC's internal speaker. With the advent of multi-timbral synths, most musicians stopped using this annoying beep and instead create a metronome track that triggers a sound from a drum machine, which is much easier to play to. Indeed, many sequencers include a metronome function that can be set up to automatically trigger a specific patch, note number, and MIDI channel for use as a metronome. Thus, the metronome function on the MIDI interface has become obsolete. If you avoid interfaces that have it, you'll also avoid the annoyance of having to turn it off. _____PURCHASING AN INTERFACE "Music Cards" are available at computer hardware and software stores, as well as through most mail-order computer hardware/software vendors. MPU-compatible interfaces -- as with most MIDI gear -- are sold through electronic music stores. Again, mail-order vendors exist through which MIDI interfaces, devices and software can be ordered. Electronic Musician and Keyboard are two magazines which include lots of ads for hardware and vendors. Many MIDI interfaces are sold in "bundles" which include a sequencer, usually an entry-level package. Unless you know FOR SURE that the included sequencer is the one you want, it's a good idea to ignore it when making a purchasing decision. The sequencer will be your primary composing tool, and deserves separate consideration. A basic MPU-401 compatible interface will work with any PC that has an open slot -- even a 4.77MHz PC. With the exception of the newer music cards -- SBPro, AdLib Gold, ProAudio Spectrum -- the cards discussed above are all 8-bit cards, and so will work with any PC. However, the more advanced functions, like SMPTE sync, multiple ports, etc., will work better with faster computers. Some older Sound Blasters and Thunderboards reportedly have some problems with very fast computers (eg 486/33's), but these are DAC incompatibilities which don't affect MIDI operation. Give some thought to the physical setup of your computer when selecting an interface. Some have their MIDI connectors on a box that plugs directly into the card on the back of the CPU; if it's hard to reach the back of your computer, you'll need MIDI extension cables (male to female). Other interfaces include a "connector box" that can be set atop or beside your computer, making cable-swapping easy. Next: "PC/MIDI BASICS #3" (MIDI#3.DOC) discusses sequencing and notation software for the PC. The PC/MIDI BASICS files are published irregularly and available in the Music & Sound Text Library of the AOL Music and Sound Forum. (c)Copyright 1991/1992 by Richard D. Clark/Fundamentally Sound. This file may be freely distributed only in its original form. Suggestions/corrections/additions may be e-mailed on America Online/PCLink to PCC RichC. ?) U \     ? w y Q X  79,.(* vDK  1!3! """9";"##_$a$"% !p!p!p!p!p!p!p!p!pS"%$%?%A%%%.&0&p'r'((***, - -9.i/k/0000?1A11133334466666k7m78899$<&<===>>>>>'?)??!p!p !p!p!p!p!p!p!p:D,  >( T$,U2h8>%  ? "%?!"(Times New Roman Symbol&Arial>"h9:e"James L. Hinkle