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Sansui MDR7 MIDI/Tape Synchroniser

Dave Lockwood casts a critical eye over this low-cost MIDI/tape sync box from Sansui.



The Sansui MDR7 is a useful little device which combines the functions of MIDI/tape synchroniser and machine remote controller for Sansui's multitrack cassette machines (MR6 and WSX1). It can also send Start, Stop, Continue, and Clock codes, plus Song Position Pointer synchronisation messages, to MIDI devices, as well as transmitting MIDI Program numbers. Rather more unusually, it will also allow MIDI to control a Sansui tape machine by translating Note On messages into the transport control codes.

MIDI/tape synchronisers can be divided into roughly three basic types: crude FSK-MIDI Clock devices, which simply instruct the MIDI unit when to start and how fast to run; timecode-based units which employ industry standard SMPTE/EBU code on tape, which is then converted into MIDI timing signals (or in some instances, bypasses MIDI altogether, talking directly to the system processor for extra speed); the third group, which includes the Sansui MDR7, uses its own form of time-stamped FSK, which is translated into MIDI clocks and transport messages, but with the addition of Song Position Pointer information, which can tell a sequencer or drum machine how far into the song it is, without always needing to start from the beginning.

The essential difference in terms of operating procedure, between the latter two types of device, which on the surface might appear to do the same job, is that the generation of the SMPTE/EBU signal is not related in any way to the speed of the track, which is why tapes used with timecode are usually 'striped' from beginning to end in one pass, often before you know what is going to be recorded on them. The SMPTE/MIDI converter then has to be told when the song starts, and what its speed and time signature are, in order to perform the necessary calculations to convert SMPTE time into MIDI clocks and SPPs.

With proprietary FSK 'timecode' devices, however, the sync signal recorded on the tape is generated under the control of the MIDI device itself, so the code cannot be laid until the speed and arrangement are firmly established - if the tempo alters at any point, so will the rate of sync pulses. Programming a start time is obviously unnecessary with this type of unit, as each section of code on a tape will be separate and (unless all your work is at the same tempo and of the same length) usable only with the musical piece for which it was generated.

SONG POSITION POINTERS



Song Position Pointers (SPPs), part of MIDI's 'System Common' group of messages, uniquely identify each point in a song simply by incrementally counting the number of 16ths from the beginning, so time signature information is also not normally required by the converter box - 64 16ths into a song is, of course, the same point in time whether you are counting in 4/4, 3/4 or 13/8, only the bar number will be different. (Technically, groups of six MIDI clocks are counted, and given the specified MIDI clock rate of 24 clocks per quarter note, that equals four SPPs per quarter note, or 16 per 4/4 bar). Devices, like the MDR7, of the 'time-stamped FSK' generation (pioneered by the JL Cooper PPS1) offer an attractive combination of economy and simplicity of operation, giving all the advantages of MIDI 'virtual tracks' which will follow your tape machine wherever it goes, without exposing the inexperienced operator to the sophistication and potential complications of a true timecode system.

CONSTRUCTION



The MDR7 is solidly built using a two-part all-metal construction, with all controls on the top surface and all connectors (three MIDI, two phono, one Remote multi-pin, plus DC In and Out) on the rear edge. The 9V DC adaptor supplied (MDR7A) is a twin round-pin version of the 'built-in to the plug' type.

There are six large, positive action, transport control switches with a small LCD window, plus a bank of secondary controls and indicators. These cover the 'striping' (code generation) functions, Auto Punch in and out for the tape machine, MIDI functions, and the entering of time signatures. Having just explained why non-timecode systems don't normally need to know the time signature, I should explain that the Sansui unit displays bar numbers while it is running and these are used as a reference for the auto-drop function; nothing disastrous happens if you enter the wrong time signature, however, but the bar numbers displayed by the synchroniser will then not agree with the actual position of the sequencer.

MIDI REMOTE



The transport controls can be selected to directly address either the tape machine or the MIDI device. When controlling the tape recorder you have a full set of Play, Rewind, Fast Forward, Pause, Record, and Stop functions, although the Zero Return and Cycle functions available on the MR6 and WSX1 recorders are omitted on the remote (they will still work if selected from the recorder, however). In MIDI mode, Play will send a Start ($FA) command, Stop sends a Stop ($FC) command, whilst Pause transmits the Continue/Stop codes ($FB/$FC). Rewind resets to the top of the track, but Fast Forward seems to duplicate Continue if the receiving device is running on its own internal clock. Setting it to MIDI clock, however, allows this control to advance the sequencer by one 8th note per press (transmitting MIDI clocks ($F8) in groups of 12), or scroll forward by running at very high speed, if pressed and held.

As the primary role of this device is MIDI-to-tape synchronisation, which requires the slaved MIDI device to be in External Clock mode, I am not entirely convinced of the usefulness of a set of MIDI remote control functions that require you to go to the sequencer to reset it to Internal Clock before you can use them. Why would you bother? Why not then simply use the sequencer's own controls? My impression is rather that the MIDI remote functions have been included simply because the commands were already in place, as a result of the tape sync system. Having said that, there is probably somebody out there who will have the perfect use for this facility, but I must admit I can't think what it might be!

TAPE SYNC



For MIDI-tape synchronisation purposes you are not restricted to just the Sansui recorders, although naturally the remote control functions will not operate with non-Sansui gear. A brief examination of the end of the 5-pin DIN remote cable with a multi-meter revealed only that simple contact closure is not the method employed, and that there are voltages present on two of the pins, so I abandoned any attempt to get it to operate other tape machines.

There are two operating procedures for initiating tape sync: Manual (for use with any recorder) and Auto-stripe (reserved for the Sansui range). In Manual mode, the Tape Out socket of the MDR7 is patched to the track to be used for sync code, whilst the MIDI In socket receives the output of the sequencer. MIDI Out can be connected back into the MIDI system input, ready for playback, and Tape In patched to the track output, without fear of generating any loops, which is the way things should always be.

Activating the Convert/Stripe button illuminates the Stripe LED and outputs a pilot tone for level setting. Recording around 0VU is recommended for -10dBV systems. Time signature has to be set by stepping through the rather limited range of 4/4, 3/4, 4/8 and 6/8. Any time signature apart from those and you will have to either dispense with an accurate bar display facility, or find an equivalent. After that it is just a matter of setting the recorder running, with the sync track in record, and then starting the sequencer on internal clock. The MDR7 then converts the stream of MIDI clock and Song Pointer data to an FSK signal which is suitable for recording on tape. ['FSK': Frequency Shift Keying - an analogue method of representing binary (ie. digital) data, using two different frequencies to represent the two binary logic states 1 and 0.]

At the end of the song, the sequencer will stop; the tape can then be rewound, the MDR7 switched from Stripe to Convert, and provided the sequencer is then switched to External (or MIDI) clock, it will accurately follow the tape in Play mode, from wherever it is started. One thing you can't do, when your sequencer's MIDI In is receiving the output of the synchroniser, is input notes from the keyboard. The MDR7 makes no provision for merging note information with its clock data, so 'MIDI Record-in-sync' is not possible without employing a dedicated merger - a clumsy solution, requiring another box and yet more cabling, which should not be necessary. A merger is not really optional in this situation, it is an essential part of any combined MIDI/tape system, and the sync box is the natural place for it.

Provided a Sansui recorder is employed, pressing the Auto-stripe button automatically sets the tape machine into Record-Pause mode, zeroes the counter and outputs the pilot tone. Pressing Start then sets the recorder running, followed several seconds later by a Start message to the MIDI device. Striping then proceeds as normal until the end of the song, when the tape is automatically rewound to zero. Synchronised playback can then be achieved, once the sequencer is switched to MIDI clock, as before, with the current bar number being displayed in the LCD window.

Like all FSK systems, the Sansui MDR7 is somewhat dependent on seeing the correct audio level coming back in off tape; too high and the speed will be erratic, tending to jump to the maximum speed of the receiving device, too low and it may tend to drop out altogether. Within the window of acceptability, the MDR7's performance proved quite efficient, with a lock-up time of two to three seconds about average for an FSK device. There also seems to be no appreciable difference in lock-up time whether the tape is restarted a few seconds from where it was stopped, or a few minutes away, unlike some other systems. FSK is usually reasonably tolerant of the odd bit of tape dropout, but entirely unforgiving of a full interrupt, however short-term, and the MDR7 is no exception, coming to a complete stop. It will manage to get itself started again several seconds later, but cannot free-wheel over the gap.

One thing to watch out for is the possibility of corrupting the reading of the sync code with a high transient level audio signal on the adjacent track - if you are putting drum machine on tape, keep it away from the sync track.

Although the MDR7 is actually only specified down to 40 bpm (beats per minute), the entire tempo range of my system (25 to 250 bpm) was tracked accurately. Some FSK devices I have tested have had some difficulty at the extremes of this range, but despite some tempo display instability due to the excessive distance between clocks at this tempo, I can verify that it still works at 25 bpm. Tempo changes within a song seem to be followed correctly, whether subtle or dramatic, so if your sequencer offers sophisticated tempo handling, you don't lose this facility, nor do you need to reprogramme everything into the sync unit, as is normally required with a stand-alone SMPTE/EBU timecode synchroniser.

All in all, the MDR7's sync performance is acceptably robust for an FSK unit, and certainly offers a viable, cheaper alternative to a true timecode device in a basic system.

AUTO-PUNCH



By combining the synchroniser with a remote control unit, the MDR7 is able to offer an automatic Punch in/out facility. The drop-in and out points are, however, restricted to just the start of a bar, which is something of a limitation in practice. It is, unfortunately, quite rare for the optimum drop-in/out points to fall right on the start of a bar - musical lines are just not that co-operative, so you frequently have to anticipate the first beat, going in, and hang over into the following bar, coming out.

I suppose it is better than not having the facility at all, but it is certainly seriously compromised. I am not quite sure why it needs to be so restrictive, other than that it considerably simplifies the number-crunching task for the 'brain' of the synchroniser to only have to recognise the start of each bar as a unique point in time. This method of operation is perhaps confirmed by the fact that lock-up during sync-play only ever occurs from the start of a bar, which means that, at slower tempos, sometimes the waiting time can be a bit longer.

To programme the Auto Punch facility, the pair of 'Measure Set' switches are employed. Hitting the Punch In button produces an LCD bar opposite the 'In Point' legend, adjacent to the display window, and a three digit number for programming. The Play button now acts as a cursor key, selecting each digit in turn, while the Fast Forward and Rewind buttons act as Increment and Decrement controls. Having achieved the desired number. Record is used as an Enter key, with the Stop switch available as Data Clear to abort the function, if necessary. Punch Out is set in exactly the same way, and you are ready to go.

After selecting the desired track on the recorder to Record Ready, you simply press Play to initiate the procedure. The Record LED on the remote flashes, as on the recorder, until the drop-in point is reached; the machine goes into record, the Record LED verifies entry, and the 'In Point' LCD goes off. At the pre-programmed point the 'Out Point' LCD disappears and the record LED goes out to confirm the completion of the recording. If you want to try again, because you messed up the part, you are required to hit Punch In, Enter, Punch Out, Enter, to recall the previously set bar numbers. A facility that is likely to be used as repeatedly as this one really should not require four keystrokes to activate it!

An alternative, and simpler, method of presetting the required drop-in points involves simply playing the tape and hitting Punch In during the bar which you want to go in on, and Punch Out in the bar following your drop-out point (it doesn't matter whereabouts in the bar you actually hit the switch, it will still always get you in and out at the start of a bar). If dropping in on the start of a bar simply will not do, you can always drop in manually via the remote, or utilise the footswitch facility - although the footswitch (momentary/non-latching type) must be connected to the remote and not to the recorder itself. It is also possible to combine the automatic and manual facilities, by perhaps dropping in via Auto Punch In and coming out on the footswitch precisely at the desired point. Well almost precisely, for inevitably with a slow moving tape format, the drop-out delay caused by the distance between Record/Play head and Erase head needs to be taken into consideration.

MISSED OPPORTUNITY



Finally, and I have left the most unconventional aspect until last, the MDR7 will allow you to control one of the Sansui recorders from a MIDI sequencer, or indeed a keyboard. The device has to be persuaded into this mode by powering it up whilst holding down the CH/PRG switch — I know of several units that enter self-testing routines in this sort of way, but not that many that use it for a standard operating mode! It powers up with a channel number display, inviting you to set the receive channel, via data Inc/Dec, followed by Enter and Convert/Stripe until the Stripe LED comes on.

Sadly, when in this MIDI mode, the MDR7 seemingly cannot also be in Convert mode, and therefore can't simultaneously be operating as a tape sync device. I am sure that this is not an oversight as a result of failing to appreciate the opportunity, so we must assume that it is perhaps an inevitable result of on-board processing power limitations.

Note On messages from C1 to G#1 are used to trigger the full range of transport functions, including Record, and include some missing from the remote - such as Zero Return and Counter Reset. If the MDR7 could perform this MIDI control function while operating in tape sync mode, then the rather 'blunt instrument' of the Punch facility would become irrelevant, for drop-ins could be preprogrammed to the utmost accuracy, down to the resolution of the sequencer, by inserting the requisite note (D#1) on the correct MIDI channel, precisely at the desired point. The recorder could then be started either directly, or from the remote, or via a MIDI Thru note message from a keyboard, with a predetermined drop-out point set by including any of the valid transport command notes at the appropriate spot.

Unfortunately, none of this is possible without tape sync at the same time, so you are left only with the novelty value of watching a tape transport shuttle about in response to MIDI notes, which very quickly wears a bit thin, for I just cannot see a really valuable practical use for this in a typical MIDI/tape setup.

CONCLUSION



The Sansui MDR7 promises much but, ultimately, delivers slightly less. It is a nice remote for a very nice tape machine (MR6) as well as being an effective tape sync device, but its MIDI functions simply do not equate closely enough to real operating situations - it rather tends to offer solutions to problems that don't exist. Any new Song Pointer-based synchroniser really should be capable of undertaking the relatively simple task of merging incoming note data with outgoing clocks, and the restrictive limitations of the Auto Punch facility are a serious compromise in practice, with the opportunity to provide more than adequate compensation via MIDI control during tape sync, sadly, having been missed.

However, I do not wish to seem unduly critical like the Sansui 10-track system I reviewed in the February issue, the MDR7 displays a desire to innovate and search into areas left untouched by other manufacturers, and as such is always to be welcomed and applauded for its implication of even more interesting developments in the future. I am pleased to be able to say that, in common with all the Sansui recording products I have had the pleasure of testing in the past few months, the last word has to be that, at only £169, the MDR7 must be said to offer good value for money simply for what it does well.

FURTHER INFORMATION

£169 inc VAT.

Fabulous Audio Technology Ltd, (Contact Details).



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Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

 

Sound On Sound - Jul 1990

Gear in this article:

Synchroniser > Sansui > MDR7

Review by Dave Lockwood

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