MIDI-to-tape sync: why you need it, what it does and how you use it.
If you think sync is the poor man's equivalent to a dishwasher, read on, as Paul White explains how you can reap the benefits of synchronising your MIDI sequencer to your multitrack tape recorder.
On their own, multitrack tape recorders are limited by the number of tracks they provide — and the more tracks you want, the more you have to pay. True, you can bounce or combine recorded tracks and re-record the result onto a spare track, but every time you do this, the sound quality is degraded and you also lose the opportunity to rebalance, pan or add effects to those tracks that have been bounced.
In the early days of home recording, there was no alternative — you just had to live with it. The introduction of MIDI sequencing changed all that. Obviously, you can't use a MIDI-controlled instrument to replace every instrument or sound that you'd normally want to record, but in the context of pop music, you can certainly use MIDI drums, bass and keyboard parts, as well as samples of instruments such as piano, brass, flute, and so on.
But MIDI is of little help when it comes to real performance, such as vocal parts, guitar solos and virtuoso instrumentals, which is where tape still has a definite place. It's true that you can sequence sampled sections of a vocal part or entire guitar phrases, but this requires a lot of memory, which adds up to high cost. Clearly the most flexible and cost-effective solution is to use a system where tape and MIDI sequencing run side by side.
The simplest scenario to imagine is where you create your backing track on a sequencer and then record this to one or two tracks of your multitrack tape machine, leaving the remaining tracks free for vocals and guitar solos. Many people work in this way, but there are several very real disadvantages.
Firstly, the sequenced parts, once mixed, can't be separately EQ'd, panned, balanced or effected — they behave just like tape tracks that have been bounced. Secondly, whenever a mix is recorded to tape, some quality is lost, and with budget cassette multitrackers, this can be quite noticeable.
A far more flexible approach is to have the sequencer running in sync with the multitrack tape recorder, so that the sequenced sounds can be fed into the final mix without ever having been recorded on multitrack at all. If the sequenced MIDI parts come from a single, multitimbral sound source with stereo outputs, then a Portastudio-type device with six or more input channels will be able to mix both the taped music parts and the sequenced MIDI parts, but if the MIDI system uses sound modules with multiple outputs or several different modules at the same time, then you'll need either a multitracker with a lot of mixer inputs or, better still, a separate mixer altogether. Fair enough, but how is this synchronisation achieved and what additional hardware is required?
We have had drum machines that can sync to tape for many years now, and though the sync facilities they offer are rather basic, they can still be very useful. They employ what is known as an FSK (Frequency Shift Keying) system, which records a series of electronic tones onto a spare track of the tape machine. These tones are related to the tempo of the drum machine, so as the tempo is increased, the electronic sync track follows.
The procedure is as follows:
If you are prepared to work in this way, you can add a sequencer to the system simply by setting the sequencer to External MIDI Sync and connecting the MIDI Out from the drum machine to the MIDI In of the sequencer. This arrangement is shown in Figure 1a, but it has the serious disadvantage that you can't record new parts onto the sequencer while you are locked to tape because the sequencer's MIDI In is taken up by the MIDI Out from the drum machine. If you intend to finish programming your drum and sequencer parts before starting work on the taped sounds this is fine, but if you want the freedom to work on your MIDI parts while listening to the tape parts you have recorded, you'll need to add a MIDI merge box to the system in order to combine the MIDI output of your master keyboard with the MIDI Out of the drum machine. Figure 1b shows how a merge box would be patched into the system. Here are a few tips to help you organise your work when you have this type of system.
A few years ago, the American Company JL Cooper came up with a refinement to the FSK sync system which they called Smart FSK. This still records the code to tape in the form of tones, but it is designed to work with MIDI Song Position Pointers so that once the code has been recorded to tape, the tape machine can be started anywhere in the song and the sequencer will be locked up to it within a second or two. Because the code is generated from the sequencer's MIDI clock, it is related to the tempo of the original sequence, so if any tempo changes have been programmed, these will be reproduced accurately when the sequencer is sync'ed to tape. The only caveat here is that you can't go changing the tempo of your sequence after the code has been recorded to tape, but you are free to change individual musical parts on the sequencer or to write new parts and change sounds. JL Cooper also saw fit to include a MIDI merge facility in their sync box, so that new sequencer parts could be recorded while the sequencer was sync'ed to tape. Figure 2 shows how a system might be set up using a smart FSK box. Note that the drum machine is now running as a slave from the sequencer's MIDI Out.
In recent years, the SMPTE (pronounced simp-tee) time code — which was originally developed for soundtrack sync in the film industry — is being widely used to synchronise audio systems. It has been used for many years to facilitate the sync'ing of two multitrack tape recorders, but it is now also commonplace in MIDI studios. Unlike Smart FSK, which is tempo related, SMPTE is based on real time measured in hours, minutes and seconds, with further subdivisions to accommodate individual frames of TV and film material. Because it is independent of tempo, a whole tape can be recorded or 'striped' with code before any recording or programming starts.
Because there is no tempo information inherent in the timecode itself, a conversion has to be done somewhere along the line, either by the computer used to run the sequencing software, or by the microprocessor inside the SMPTE-to-MIDI sync box. The starting tempo of a piece of music and the location and amount of any subsequent tempo changes are stored in the form of a 'tempo map' which must be used alongside the sequencer data whenever the sequence is run sync'ed to tape. On a modern computer-based sequencer such as C-Lab's Notator or Creator and Steinberg's Cubase, dedicated SMPTE sync units are available which handle the creation and storing of tempo maps via the sequencing software itself. This makes life much easier than having to treat the tempo map as an entirely different subject, though some of the newer stand-alone units also automate as much of the procedure as is possible.
So, why go to the bother of using SMPTE? What advantages does it offer? Unless you are planning to work to picture, then the answer is that SMPTE offers little more than a smart FSK system. Both allow you to start at any point in a song and both will look after your tempo changes, smart FSK doing so automatically. Both will follow changes in tape speed caused by general drift or by deliberate varispeeding, but you have to keep in mind the fact that your taped sounds will increase in pitch if you speed up the tape, whereas the sequenced MIDI sounds will remain at their original pitch.
In SMPTE's favour, it does allow you to stripe the tape first, whether you have programmed any sequence or not, while smart FSK requires that you have programmed your sequence, at least as far as its length and tempo goes, before you start work. Furthermore, if you do decide a tempo change is in order, you have to re-stripe with a new FSK code, whereas with SMPTE you simply have to create a new tempo map. But in practice, these differences are fairly minor.
A relatively new variation on the sync code theme is MIDI Time Code, which is essentially a MIDI interpretation of the traditional SMPTE protocol. New sync boxes such as JL Cooper's PPS2 can read and write MTC, but many of the sequencers in common use aren't equipped to make use of it. There's also a dedicated sync code known as Direct Time lock or DTL, which is used exclusively by Mark of the Unicorn sequencing packages.
When working with a cassette multitracker, even the better-equipped models tend to be short of mixer inputs unless your MIDI system is relatively simple. A separate mixer offers greater flexibility; the audio quality is often better, there are more comprehensive facilities and you can choose one with as many input channels as you require. The three tape tracks used for audio can be plugged directly into the line inputs of the mixer if the multitracker has separate tape outputs for each track, but all is not lost if there are only stereo outputs. In this case, you can mix the three tape tracks to stereo, using the mixer section of the multitracker, and then feed these into two channels of the mixer panned hard left and right to retain the stereo mix you have set up. Figure 3 shows a typical setup for mixdown.
It's also possible that you can use the Foldback or Pre-fade send of your multitracker to provide a further output allowing you, for example, to send track one to the Left stereo output, track two to the Right stereo output and track three to the Foldback output. The possibilities vary from machine to machine, but a little lateral thinking often produces a way around a seemingly tricky problem.
The MIDI instruments are fed into the remaining line inputs, and whatever effects units are connected to the mixer can be used to process both the taped and sequenced sounds. Because the MIDI instruments have never been recorded onto tape, the quality of the final recording is largely determined by the quality of the mixer and the tape recorder used to record the final stereo mix. In this respect, a budget DAT machine can be used to produce near CD-quality results, even when working with a modest 4-track recorder.
The other benefit of working in this way is that you can always change the sounds on your MIDI instruments, right up to the moment before you mix. This very flexibility has led some record producers back to recording their MIDI instruments onto tape because they find that leaving everything open-ended can invite unnecessary tinkering, which wastes time and money. In the professional studios, where recording quality is good and tape tracks are abundant, this can make a lot of sense, but in the home studio, where time is free and tape tracks are scarce, sync'ing may be all that keeps you afloat!