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XRI XR300 Synchroniser

SMPTE Synchroniser

Still on the sync track... Chris Jenkins sets the pace with a SMPTE/MIDI converter designed to give all the higher functions of SMPTE tape synchronisation without the higher price-tag.


As the inevitable advance of technology makes yesterday's luxuries today's standards, budget SMPTE is quickly becoming the synchronisation order of the day; the latest offering is the XRI XR300.


HAVING HAD ENOUGH trouble coming to terms with the theory and practice of MIDI, I'm sure that some of us are experiencing a certain reluctance to tackle new and equally jargon-ridden topics. A case in point: SMPTE. Fortunately, with the rapid drop in equipment costs, SMPTE has become increasingly user-friendly. The XRI XR300, for example, is so straightforward and inexpensive that I can see it making its way into thousands of studios of both amateur and professional standing.

For the uninitiated, SMPTE addresses two problems; that of synchronising audio tracks with visuals (film or video), and indirectly that of synchronising successive takes on multitrack audio recordings. Several systems exist which will lay down a synchronisation track on one audio channel of a multitrack recorder. Korg's £149 KMS-30 MIDI Synchroniser, and XRI's own £59.95 XR01, can transform a MIDI clock into a sync pulse, transmit it to tape, then read it back and sync subsequent audio tracks using MIDI or DIN sync. The drawback with these systems is that the sync tone laid down on tape consists of just a start signal, and a continuous sequence of clock pulses. The result is that drop-ins are out; if you need to re-take a track, you have to rewind to a point before the sync tone on the tape and start all over again.

Enter SMPTE. The SMPTE (Society of Motion Picture and Television Engineers) standard is a much more sophisticated affair than its timecode brethren. It's a digital signal which includes timing information in hours, minutes, seconds, frames and bits. Put a SMPTE code on one track of tape and then, on playback, you can lock into the code at any point, identify that point in the recording, and transmit appropriate MIDI song-position pointers and clock information to any suitably equipped sequencer or drum machine.

The Prototype



THE XR300 IS a 19" rack-mounting unit, based on a successful free-standing version, the XR03. The review model was pre-production and, while XRI will not be spending unnecessary ackers on cosmetic effects, the final model will be professionally finished with silk-screened legends and a custom-designed shell.

The XR300 can use any of the established SMPTE standards; 24, 25 or 30 frames per second, and "drop-frame". On powering up, the device defaults to Control Mode. Any of the six main functions can be entered from here by pressing a single key; everything is very logical and clearly laid-out.

The first function is Rate, which allows you to set the required SMPTE frame rate. Obviously, if you are syncing to film or video then you need to select the correct rate for the visual format you're using; if you're just syncing to your own tape, it doesn't matter which you select, so long as you use the same rate consistently.

The cursor and Run keys are used to select a rate, and, if required, a "ppqn" (pulse-per-quarter-note) rate for non-MIDI equipment. Rates of 24, 48 and 96ppqn rates are available. SMPTE allows you to set the duration of your SMPTE signal. The start time can be adjusted to any value you require, though normally this would be 00:00:00:01:00 (hrs:mins:secs:frames:bits). The audio output level to tape can be widely adjusted using the Trim control until a level of about -5VU is achieved. First you need to "stripe" one track of tape. Unlike the more usual audio timecodes, this is done before commencing recording. All you do is start your audio tape, press Run on the XR300, and watch as the LED records the SMPTE signal to tape. Press Exit when you've striped enough tape, and that's the complicated bit done.

The Procedure



FROM THAT POINT on, it's hardly necessary to worry about the XR300 at all. You can wind to any point of the striped tape, and, on playback, the XR300 will lock onto the tape (taking just over a second), locate the timing position, and generate the appropriate MIDI start signal, song pointers, clock rate, and DIN sync for your sequencers and drum machines to read.

The Tempo function allows you to set a time in hours, minutes, seconds and frames at which the XR300 will begin to generate MIDI clock signals, so your music obviously doesn't have to start right at the beginning of the SMPTE stripe. I found it a good idea to give the XR300 at least five frames in which to determine the correct MIDI clock speed before starting.


You can also program changes in MIDI clock tempo during the song. The default is 120bpm, but up to 10 tempi can be set, together with the number of bars for which the tempo lasts - up to a maximum of 250. Maximum song length, then, is 3000 bars. You can of course reprogram any tempo setting individually, and if you want a tempo to last for more than 250 bars, you just program the same tempo more than once.



"The Mode function allows you to introduce an offset to compensate for differences in timing response or to give a particular 'feel' to a part."


The Mode function allows you to introduce a delay or advance into the synchronisation between the timecode read off the tape and the MIDI clock generated. This is usually known as an "offset". You could, for instance, record a drum track, then rerecord it with a slight offset to produce a double-tracking effect. More substantial offsets, produced by changing the start time, would of course produce an echo effect but most common use of the facility is to compensate for differences in timing response of different pieces of equipment or to give a particular "feel" to a part. The minimum offset is one bit (1/80th of a frame, or about half a millisecond).

The usual working mode of the XR300 is Read, where it locks onto and displays the timecode from the tape, and generates MIDI and DIN sync codes. As this happens, incoming MIDI data can be merged with the clock data, and transmitted to each of the three outputs. Tape errors in the incoming code are displayed on the LED display, but the XR300 is very tolerant of faults and will normally not be affected by drop-outs.

The clock outputs are generated until the tape stripe runs out, or until the total number of bars programmed into the XR300 ends. Alternatively, you can stop the tape at any point; the XR300 will generate stop commands, and you can then rewind to any point on the striped tape, start again, and the XR300 will lock in and derive all the correct timing and position information all over again.

The MIDI song pointer is basically a count of the number of 16th notes which have elapsed since the start of the sequence. To make use of the XR300's facilities, you'll therefore need a drum machine, such as the Yamaha RX series, or a hardware or software sequencer such as Steinberg Pro24 or Iconix, which recognises MIDI song postion pointers. Older drum machines such as the Sequential Drumtraks don't respond to SPP so they're less flexible when used with SMPTE code.

The Machine



WHILE THE XR300 has a short-term memory store (the duration depends on how long the unit has been in operation), it can also dump all its settings to tape or any MIDI data filing system using System Exclusive codes. The Dump/Load function should normally be used if the XR300 has an external 9V power supply. The LED on the pre-production model generated a very small level of background noise, but the production version will have the power supply built-in, and will feature a gating system to eliminate unwanted noise.

More powerful versions of the XR300 are already in the planning stages, and a PROM change may well allow users to update their systems. One possibility is that later versions will feature the ability to memorise MIDI patch changes, and will have more sophisticated MIDI merge functions. XRI's XR02 MIDI Merge box is currently available; it features two In, one Thru and two Merge Out sockets, and can be used, for instance, to allow both a keyboard and a sequencer to control a synthesiser module simultaneously.

Verdict



ROLAND'S SBX80 AND the Steinberg SMP24 played a large part in introducing SMPTE to many musicians, though at a price of many hundreds of pounds. Earlier this year the Nomad SMC helped bring SMPTE down to under £350. More sophisticated systems, such as the forthcoming Bokse SM1 will offer more sophisticated implementation of the SMPTE standard but not without adding a hundred pounds to the cost of the Nomad.

While the Nomad is inexpensive, easy to use, and flexible, the XR300 is cheaper, simpler and more powerful. For my money, then, the XRI XR300 looks like the best bet in the SMPTE market for some time to come.

Prices XR300 £250 including VAT; XR02 £64.95

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Fumbling in the Dark

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Picture Scoring


Music Technology - Copyright: Music Maker Publications (UK), Future Publishing.

 

Music Technology - Jan 1988

Donated & scanned by: Mike Gorman

Gear in this article:

Synchroniser > XRI Systems > XR300 Synchroniser

Review by Chris Jenkins

Previous article in this issue:

> Fumbling in the Dark

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> Picture Scoring


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