Return to Zero (Part 5)
Multi-tracking and Overdubbing
This month we examine basic multitrack techniques including overdubbing and drop-ins, and explain about sync.
If you had been a recording artist back in the early 1960's, your songs would have been recorded direct onto a mastering machine. Everything, including the singing would have been performed simultaneously so that the finished result was in fact a recording of a live performance. However this technique had several disadvantages; the sound and balance of all the instruments had to be decided upon before the final recording took place, with the resultant wastage of the musicians' time. Also, the fact that everyone involved had to be in the same place at the same time was naturally inconvenient. Overdubbing (adding extra instruments) could only be achieved by playing the track back on one machine and re-recording it onto another while mixing in the additional instrument (again played 'live') with the original track in the correct balance. However advancing technology (and no doubt the rapid expansion of the popular music industry) brought about the introduction of the multi-track machine, which records several tracks side by side along the length of the tape. These days this can involve from as few as 4 tracks up to as many as 36 (and even more if two machines are synchronised together).
With many tracks at your disposal, each instrument or vocal take can be recorded on its own track enabling recording or re-recording of any one part without affecting those already recorded. This overdubbing facility can increase the apparent number of musicians so that one person may, if they wish, play every part. Having everything on its own track also allows separate treatment of each composite part using EQ and effects, and the changing of the balance of the instruments in the mix. The more tracks there are available, the less mixing together (bouncing) of instruments has to be carried out before the final mixdown into stereo takes place. But even with as many as 24 tracks available, engineers often still find themselves having to bounce a number of tracks together in order to fit everything on!
Sadly, the cost becomes greater the more tracks you want and is not even directly proportional to the number of tracks, (an 8-track machine will cost you more than twice a 4-track for instance) so most home recording engineers' budgets will only stretch to a 4- or 8-track machine. However very good results have been and are frequently achieved. It's quite well-known that the Beatles recorded their 'Sergeant Pepper' album on 4-track machines.
The principles involved are the same for small machines as for larger ones, in that the electrical signals received from the mixer or microphone are first processed by a recording amplifier and then changed into magnetic signals by the Record Head which magnetises the tape. On playback the magnetic tape produces tiny electrical signals in the Playback Head which are processed to provide an output to a (usually) separate amplifier and speakers. On some machines the Record and Playback heads are combined. There is also another head called the Erase head, which removes any signal which has been previously recorded. This is the first head the tape encounters and is activated when the machine is put into the Record mode, so that any track that is in Record mode is first wiped clean before any new signal is recorded.
Anything which prevents a close contact being made between tape and heads prevents the signal being recorded or played back properly, causing the signal to 'drop-out'. This can be dirt on the heads, or on the tape, or else creases in the tape caused by accident or poor storage. In the case of reel-to-reel machines, the tape should be wound evenly onto the spool giving a smooth surface. To achieve this it's a good idea to play your tapes through at normal speed after a recording session as fast winding invariably results in uneven spooling. If your machine spools very unevenly you should get it serviced as in this case it's all too easy to crease the edge of the tape when removing the spool from the machine.
The actual quality of the recording is dependent not only upon the standard of equipment and quality of tape used, but also upon the area of tape designated to each track. In general the wider the track spacing and the faster the tape speed, the better the quality. All 24-track machines use 2 inch tape, most 16-track machines use 2 inch or 1 inch, most 8-track machines use 1 inch or 1/2 inch, and both 4- and 2-track reel-to-reel machines use 1/2 or 1/4 inch tape. The Fostex company has shrunk tape width requirements considerably, using 1/2 inch tape on their 16-track machine, and 1/4 inch on 8-track, which is the same track spacing as used on cassette-based 4-track systems (four tracks on 1/8 inch tape). With tracks being so close together you can get crosstalk problems where a particularly 'peaky' signal (hi-hats or a sync-code for instance) has bled from one track onto one or more adjacent tracks. The only way to get round this is to record particular offenders at a lower level than usual. Fortunately, many budget recorders have built-in noise reduction which improves the crosstalk performance.
It's always a good idea before starting your recording to decide exactly what instruments you're going to need on the song and where you're going to put them. Professional studios use a grid-style layout called a 'Track Sheet' for this. It's especially important when you've only four or eight tracks to play with as you can't therefore afford to have every instrument on its own track. If you were, for instance, a solo artist playing everything yourself you might decide that you need a drum-machine, bass guitar, keyboard, lead guitar and two lots of vocals on your composition. If you're working with four tracks this will necessitate some bouncing (sometimes referred to as 'ping-ponging'), as there are six 'layers' to fit onto 4 tracks. The general rule is to have as few bounces as possible, as the signal deteriorates and hiss is added each time.
It's often easiest to record the rhythm track first, so that you have something to keep time to. Indeed if you use a drum machine you'll have to record it first, because you won't be able to synchronise it to your playing (unless you use some sort of time-code which you would then have to record onto your tape). The order in which you record the remaining tracks doesn't really matter but it's easier to mix if you record backing or rhythm instruments first, and add vocals and lead instruments last. This also ensures that the most prominent part of the track has the least generations to go through and so will retain its good quality. The same principles apply when using 8-track, except of course you have twice as many tracks to play with and can therefore record more instruments before you have to bounce.
There are a number of ways of doing bouncing on a 4-track. It should be remembered that any effects on individual instruments should be added as you bounce, because you won't be able to do this later without affecting the other instruments on the same track. You can record three tracks and bounce them across to the fourth track, using either the machine's inbuilt mixer if it has one or an external mixer, leaving the first three tracks free, this means that you are stuck with the mix (in mono) of your first three tracks, because this method necessarily involves erasing the original three tracks as further tracks are added.
Another way of bouncing involves the use of a 2-track machine (cassette or reel-to-reel, whichever you master onto). This is done by recording on all four tracks of the multi-track machine, mixing these onto the 2-track machine into stereo, and transferring this back to two tracks of the 4-track, then filling up the remaining two tracks. This has certain advantages over the first method in that the first four tracks end up in stereo, and also you can transfer the mix back to a fresh piece of tape so you can always go and re-mix the original four tracks if necessary. On the minus side, this method involves two bounces instead of one.
If more than six tracks are needed you can always do more bounces, but the problem with this is that after numerous bounces the first tracks recorded will have gone through so many generations that they will show a distinct loss of quality. Another way to economise on bouncing is to add an instrument 'live' as you bounce. You have to play the part correctly all the way through, though; no drop-ins are allowed! 'The Ten Track Bounce', which is a way of recording ten tracks on 4-track, is achieved by recording three tracks, bouncing these onto the spare track adding an instrument as you bounce; recording two more tracks, bouncing these three tracks together adding another as you bounce; then filling up the remaining three tracks.
Okay, so you've written out your track sheet and decided what order you're going to record in and what you intend to bounce where. You start by recording, for instance, your drum machine onto track 1 and decide to record the bass on track 2. This is when you could get synchronisation problems. It all depends whether your machine records and plays back off separate heads, or uses the same head for both operations. Many modern budget machines (including cassette based systems) opt for the latter, as this can keep manufacturing costs down. Some machines (like the Teac 38 8-track) have a 'normal' head and a 'repro' head (which are actually identical in this particular machine), but only the 'normal' head is used when recording. The 'repro' head is only used when setting up the machine, so it really belongs in the latter category. If yours belongs in the former category (the Teac A3440S is one example), you will find that if you record your bass track while playing along to your recorded drum track, the bass will be slightly delayed in relation to the drums on playback. This is because you're listening to the drums off the playback head and recording the bass onto the tape with the record head, and there is a significant amount of tape between the two! The way manufacturers get round this is to enable you to play back off the record head whilst recording, and there will be a switch or series of switches (labelled 'Sync', 'Simul-Sync' or 'Sel-Sync') for this purpose, either for selected tracks, or all tracks not in record. Often the quality of playback off the record head is not as good as it would be if it were played off the playback head, but it is usually good enough for monitoring purposes.
You will also have problems with sync using a machine with separate record and playback heads if you record three tracks and decide to bounce two of them together onto the fourth track, as the two tracks you have mixed will be out of sync with the one you haven't, again due to the distance between the record and playback heads. Many home recording machines these days (including the Fostex A8 and B16) only have the one head for record and playback and this problem cannot occur. On some of these machines however, you have to leave one track between those you are bouncing from and those you are bouncing to in order to avoid feedback problems.
A 'drop-in' is the term used to describe the process of switching one or more tracks of a recorder to 'record' whilst the tape is still running in order to replace an unsatisfactory part of the recording with something which is hopefully more suitable. This is simply accomplished on most machines by holding down the 'play' button and then hitting the 'record' button at the appropriate time. Dropping out is simply accomplished by pressing 'stop' or 'pause' followed by 'stop'.
Most modern machines will give a click-free drop-in and drop-out, but there are a couple of points to watch. Because of the distance between the erase head and the record head, there is bound to be a slight overlap of signals during a drop-in as up to half a second of the old recording may be past the erase head when you hit 'record'. This is not usually noticeable, but it is always as well to hit 'record' on a drum beat to mask any discontinuities.
Dropping out again is more of a problem because the point at which you hit 'stop' will always be followed by a short stretch of silence, again caused by the gap between the erase and record heads so you must try to drop out during a pause in the music or on a drum beat if the former is not practical. Some machines now incorporate a footswitch for dropping in and out which makes life very much easier.
Be warned! Multi-tracking is addictive, and once you've been bitten by the recording bug you'll get caught in the never-ending spiral of continually wanting to upgrade your gear! When limited to four tracks you really have to reach a compromise between the number of instruments and the loss of quality which too many bounces results in, and find the way that suits you best. It also pays to look after your gear, read the manual that comes with it and obey any maintenance instructions (such as the de-magnetising and alignment of the heads) to the letter - and don't forget to use the best tape you can afford. Also keep the tape heads and tape guides clean as this not only produces better recordings but also reduces head wear. The good news is that judging by the tapes we are sent every week by the readership of this magazine it is perfectly possible for very good results to be achieved with relatively modest equipment and even the odd record deal to be clinched!
Feature by Shirley Gray
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