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The Mac Serial Port; Romulus PCI card; Opcode Optical Port; All About Plug-ins

Apple Notes By Martin Russ
Published April 1999

The Romulus PCI card provides four MIDI‑capable serial port interfaces.The Romulus PCI card provides four MIDI‑capable serial port interfaces.

Just as the Universal Serial bus arrives, the FireWire juggernaut sounds its horn and releases the air‑brakes. Martin Russ boldly attempts to fight off the worst of the bad puns.

>Rather like the nasty little aliens that frequently inhabit SF movies, things move fast these days. The new 300, 350 and 400MHz G3 Macs had barely had time to arrive before MIDI solutions began to appear. TSC produced an entire digital audio and MIDI software and hardware system, and Mark of the Unicorn produced adverts showing a spoon with U, S and B spelt out in alphabet cereal shapes, and cracked the 'Universal Cereal bus' on an unsuspecting world. And I'm told that my puns are bad [They are — Ed].

But this does not disguise the underlying message. USB has been kick‑started by the iMac, and whereas a couple of months ago USB and MIDI weren't often seen in a sentence together, they are now definitely serving time in the same cell. USB add‑on cards are appearing, and the picture for those USB‑to‑Serial Port adapters seems to be stabilising — with some manufacturers now stating exactly what they will and won't work with (the latter with MIDI interfaces, for example, in one case) — although the actual story is more complex than some manufacturers are suggesting (see below for the full horror).

Beyond USB, there is FireWire. Serial again, but faster than the fastest SCSI, and hot‑pluggable too. FireWire may take a little longer to get going than USB, and I can't see SCSI going away for some time, but I suspect that in less than a year we will be seeing the first audio applications for FireWire. The iMac drove the USB, and the new G3s ought to drive FireWire. I'm watching the Internet to see if FireWire suddenly explodes like USB did!

The Mac Serial Port

Opcode's OpticalPort offers a USB audio solution featuring two channels of S/PDIF and 20‑bit analogue‑to‑digital conversion.Opcode's OpticalPort offers a USB audio solution featuring two channels of S/PDIF and 20‑bit analogue‑to‑digital conversion.

I warn you now that there's no such thing as a simple answer. Probably not to anything, but definitely not to serial ports. Especially Mac serial ports. Let's start with the obvious: there are usually two ports, a Printer port and a Modem port. Except that some PowerBooks don't have the Modem port, and not forgetting that you can plug a printer into the Modem port and still use it (and vice versa!). And you can plug a MIDI Interface into either port, and some into both at the same time. Does that give you some of the flavour of a less‑than‑simple answer?

The Mac's serial ports produce streams of digital information in at least three different formats. The word 'serial' refers to the fact that the information is all bundled up together so that it fits on to a single piece of wire — but after that, several other wires are needed to provide a ground connection, control functions and so on. Even so, a serial connection normally requires significantly fewer wires than something like SCSI, which is a parallel format where multiple wires carry the information spread across them.

The first format is the one which PC users would expect from a serial port: plain and simple transfer of a stream of information. This is the format which a simple low‑cost printer or a modem might use. Strictly, the port is an RS422 port, but for most practical purposes, this can be regarded as being virtually the same as an RS232. The second format is the ingenious solution to networking which Apple used to call AppleTalk, but which is now called LocalTalk. It uses the printer port to carry a slow‑speed serial network connection, which can be thought of as a slow version of the Ethernet LAN connections that you find on most Macs now — AppleTalk runs at 240 kilobits per second, whilst Ethernet starts at 10 megabits per second and goes upwards. AppleTalk is used for networked printers and for sharing files between Macs.

The third format makes use of the inherent flexibility that Apple have provided in the serial port hardware. The reason that you can have a conventional serial port and an AppleTalk port sharing the same socket is that it is possible to reprogram the interface chip to carry out a number of different serial formats. Some Mac MIDI Interfaces take advantage of this, and use their own proprietary formats for making the most of both serial ports. The plain and simple single‑port MIDI interface boxes tend to use a very straightforward format, employing a 500kHz or 1MHz clock for synchronisation (very reminiscent of the MIDI Interfaces for the BBC B, Spectrum, Commodore 64, and so on), but beyond this there is no standard.

Converting from USB to Serial Ports is thus not as straightforward as it might appear. The simple serial port is easy to emulate, as is the AppleTalk port. But catering for all of the possible MIDI (and other serial port) uses isn't easy at all. Hence the caveats that you will see on USB‑to‑serial port converter box specifications ('works with many printers'...). The bottom line here is to check before buying and, preferably, to see it working first (and on THEIR computer!) — but then that applies to almost any computer hardware‑related purchase.

Serial Solution?

VSamp allows you to play samples from a MIDI sequencer via OMS or FreeMIDI.VSamp allows you to play samples from a MIDI sequencer via OMS or FreeMIDI.

Hinton Instruments may have provided a solution to the G3's lack of serial ports — as well as my constant switching between AppleTalk, serial printer and MIDI Interfaces. They are UK and European distributors for the MegaWolf Romulus and Remus PCI cards, which give either four or two serial ports with the Mac‑standard mini DIN‑8 sockets (see this month's news pages). The cards have been selected by Hinton Instruments because of their ability to support MIDI interfaces as well as conventional Apple serial printers and modems — and they are claimed to have superior performance to USB‑based solutions (with this in mind I'll be looking at these cards in more detail soon).

The cards may be used on any Power Macintosh with an available PCI buss slot, and are compatible with all Macintosh 'Standard' (the basic single‑port) MIDI Interfaces and some multi‑port interfaces — more details can be obtained from the Hinton Instruments web page.

Mark of the Unicorn's FreeMIDI 1.38 supports this card, and OMS support is due soon.

Romulus (gives four serial ports) £299 including VAT.

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USB Today

For those who do want to go down the USB route, Apple's web site now includes lots of information about MIDI and USB, with current and forthcoming products from many manufacturers. When I visited it had pictures and links for: Emagic's forthcoming AMT8 8x8 MIDI Interface for USB or serial port Macs (or PCs), due April 1999; MIDIman's USB MIDISPORT 2x2; Roland/Edirol's SMPU‑64 USB MIDI interface; MOTU's developments of USB MIDI Interfaces; and Opcode's MIDIport 32 (one MIDI port), MIDIport 64 (two MIDI ports), and STUDIOport AMX with audio and MIDI via two audio inputs, S/PDIF digital outputs, four MIDI Ins and Outs and SMPTE‑to‑MTC conversion facilities. Opcode's DATport USB audio interface has already been mentioned here, but it is now joined by the OpticalPort+Analog with two channels of Toslink S/PDIF, analogue I/O via 20‑bit converters, and the DATport+Analog which has phono‑socketed S/PDIF combined with 20‑bit analogue audio I/O. Mac audio drivers for USB are expected in early Spring 1999, which should be about the time you read this.

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SCSI, Samplers & CD‑Roms

I have had more email about accessing Mac CD‑ROM drives from a sampler. Subjects such as multiple SCSI busses in Macs (some Macs have separate internal and external SCSI busses), and SCSI dumps, plus some aspects of SCSI buss control seem to be causing confusion. I've been looking into this and a forthcoming article will try to answer the questions in more detail.

Tip Of The Month: Triggers

Another solution to the problem of triggering audio samples from a sequencer (I suggested using D‑SoundPro as one solution some months ago) is to use VSamp. Malcolm Haylock's VSamp is a $25 shareware OMS‑ or FreeMIDI‑compatible multitimbral sample playback application. It allows you to load up a bank of samples (or load samples singly and then save them as a bank) and then assign these to MIDI channels which can be controlled from a MIDI sequencer.

As an alternative to QuickTime GM samples or a full MIDI + Audio sequencer, VSamp is an excellent tool to investigate if you need more than just MIDI sequencing. As a one‑time MIDI‑only person, I must warn you that being able to sequence samples directly instead of via a sampler is very addictive. Thanks to Jack Spence for reminding me about VSamp.

All About Plug‑ins

Lots of people I talk to seem to be unsure about plug‑ins, so I thought it might be useful to explain exactly what they are and what they can and can't do.

So, what's a plug‑in? The name comes from hardware, where some devices were designed so that components could be easily changed. For example, my video recorder has the option of an add‑on card which allows it to use the PDC system so that I should record what I intended to record, even if it gets moved earlier or later in the programme schedule. And that's what plug‑ins are all about — they allow you to enhance or expand the capability of a device. Optimists think of this as preventing early obsolescence. Pessimists see it as a way of being charged for extra functions that should have been included as standard.

In computers, plug‑ins have appeared where a very successful application has become dominant, and where the users of that application have a wide range of specialised requirements which are not easily met by the resources of the application software producer. Plug‑ins allow third‑party companies to produce specific enhancements intended for those custom needs, and they allow the application developers to concentrate on getting the core software right without lots of diversifying distractions. It's an arrangement that works well, and some plug‑ins have become the basis of major companies.

Perhaps the best‑known example in the wider Mac world is Adobe's Photoshop, where the provision of a simple plug‑in architecture was intended to allow extra filtering algorithms to be added to the blurring and sharpening tools that were included as standard. Kai Krause was one of the people who produced additional filtering tools, except that his combination of radically different user interface concepts and wildly inventive filtering functions helped turn a photo‑retouching tool into a creative graphics art tool.

The basic format of all plug‑ins is the same: the application has a defined interface that allows third parties to add extra functionality by sending data to the plug‑in, where it is manipulated and then returned to the application. Writing your own plug‑ins from scratch isn't all that straightforward, although there are some utilities which make it easier by providing additional help and simplifying the programming knowledge that is required (we will look at some of these in the coming months). In a MIDI + Audio sequencer, plug‑ins usually provide audio processing effects such as EQ, phasing and flanging, echo, reverb, and compression. Remember that what you can do with a plug‑in is restricted to the interface that is provided by the application. If it only allows you to process the audio data during playback, you won't be able to write a neat sample‑editing plug‑in.