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Analogue Versus Digital Tape

Tips & Techniques By Craig Anderton
Published March 1994

Changing from analogue to digital multitrack brings many benefits and one or two pitfalls. Craig Anderton offers some hints and tips to help you get the best from digital recording.

I recently replaced my venerable Tascam Model 58 analogue 8‑track with the Alesis ADAT which, in case you've been living on Mars for the past couple of years, is an 8‑track digital audio recorder based on S‑VHS technology. I was expecting better sound quality than analogue, no need for noise reduction, and cheaper tape costs, and was not disappointed. But I've found that going digital has some ramifications I didn't expect.

To lessen the culture shock for those who are succumbing to the temptation of translating music into numbers and back again, here are some the things I've learned about life in the Digital Tape Age. Although the following is based around ADAT, most of these observations will probably apply to digital recorders such as the Tascam DA88 and the Fostex‑branded ADAT that is due to arrive soon.

Digital Pointers

  • You can trust your tape counter. With ADAT, the counter readings refer to the time code that ADAT writes to an 'invisible' control track (this is the same track that provides sync information when synching multiple ADATs). Readings never slip, so you don't have to re‑zero the counter every 10 minutes or so.
  • You can forget about modulation noise, audible print‑through, noise reduction pumping, wow, flutter, hiss, scraping reel flanges, or a guard track for time code. Speaking of which, having the extra track is so nice, it's good to know that...
  • don't need to give up a track for time code any more. There's a lot of MIDI Machine Control code flying around ADAT's innards, and JL Cooper (justly famous for coming up with nifty little widgets, and usually doing it first) makes a box that generates MTC code from within the machine itself, obviating the need for a separate time code track.
  • The 'continuous SMPTE sync' option with Sound Tools is useable. Sound Tools can sync to tape in two ways: SMPTE start, which starts Sound Tools at a particular SMPTE time and then free runs, or continuous SMPTE sync, where Sound Tools 'tweaks' its timing to conform to the code coming from tape. And that's the problem — even with decent analogue decks, there's a bit of drift. As Sound Tools (which doesn't drift) compensates for these timing changes, it creates pitch shifts that sound like an off‑center record (or what happens to the voices of people in science‑fiction movies when they go through time warps, in case you're too young to remember what vinyl records were like). Setting a start point is generally the better of the two options, although eventually Sound Tools and tape will drift apart, at which point you have to set a new start point and record the next segment — at least until it drifts again.

Well, digital doesn't drift, ADAT doesn't drift, and time code recorded on ADAT doesn't drift. End of problem.

  • Avoid the pitfalls of virtual tracks: virtual MIDI tracking — where you sequence MIDI‑driven sounds, record acoustic sounds on tape, and sync the two together to gain more tracks — has been a boon to project studios. But virtual tracks also have limitations. When you're doing the mix of your life and get a stuck MIDI note (or one of the MIDI instruments goes into that particular kind of mindless hyperspace that seems to be part of the genetic background of digital gear), virtual tracks don't seem like such a good idea. The same reservations apply if you have to redo a mix and just can't get the levels and signal processing effects for the MIDI tracks exactly as they were.

So if you get a pre‑mix you like of the virtual tracks, record it on tape. Granted, that uses up two tracks, but sometimes it's worth it. And if you're desperate, you can always replace those tracks with overdubs and go back to doing virtual tracks.

Here's an additional tip: if you're going to record a virtual track pre‑mix on tape, record a rough version first and do your acoustic overdubs to that. Then when you go all‑out for your virtual track pre‑mix, you can do it in context with the overdubs.

  • Eliminating MIDI Time Code jitter: compared to synching to an internal clock, sequencer timing goes to hell, or at least Houston in late July, when synched to MIDI Time Code. Okay, it's not really the fault of MTC per se, but the processing speed of computers and the quality of a sequencer's coding. Still, I was working on a dance tune recently and when the sequence was synched via MTC to SMPTE, not only did the kick drum wobble, in a couple of places the sequence had what could only be described as the digital equivalent of a seizure.

The solution? Run the sequencer from its internal clock, record the sequenced pre‑mix directly to tape, and overdub the other tracks — just like the old days. Who needs sync?

When it's mixdown time, you'll still be able to run a MIDI fader unit from the sequencer. Timing requirements aren't as tight for mixing moves, and fortunately, glitches tend to happen in the same way each time so there won't be a different mix every time the tape plays back.

  • Ah, the grunge of analogue tape. Some people complain that digital sound lacks soul and warmth and possibly promotes both tooth decay and wanton sexual practices. Although I generally like the sound of digital, many people don't realise how much they use analogue tape's saturation characteristics until it's not there any more (especially with drum sounds and vocals; guitar parts are often so distorted that you'd never miss a few per cent of THD). Here's a workaround.

Find yourself a studio‑oriented multi‑effects unit with distortion (intentional distortion, that is), since distortion can sound great on electronic drums. A little bit of overdrive acts as a hard limiter, and 'crunches' the drums as it compresses them (I also throw in a little EQ to brighten things up). The sound quality is awesome, and what's really odd is that you can't tell the drums are being distorted, even with what seems like a lot of overdrive. But it's better than tape distortion, because you can control it, and you don't saturate the high frequencies. Try a little overdrive on your drum machine some time — the results may surprise you.

For vocals, the distortion has to be a lot more subtle. A tube mic preamp with just a hint of distortion seems just about ideal — though they can be rather expensive. I'm not a hardcore tube fanatic by any means, but when it comes to vocals, I've seen the light.

  • Backup for cheapskates: the expensive way to back up an ADAT tape is to get another ADAT and do a digital dub. The cheap way (assuming you have a DAT recorder that syncs to SMPTE) is to sync the DAT to ADAT and record four pairs of tracks onto the DAT. Should anything happen to the master tape, you can always restripe an ADAT tape with SMPTE, drive the DAT machine, and re‑record the DAT tracks onto ADAT.

Don't have a SMPTE DAT machine? Well, because of digital's lack of drift, if you fly in parts and they sync up at the beginning (usually through dumb luck), they'll stay in sync until the end of the tune. Some people have reported running non‑synched DATs for 30 minutes or more without drift.

There's a trick to this: first, back up your stereo (or mono) drum tracks on DAT. Next, record another track, such as bass, along with one of the drum tracks. Then record another track and one of the drum tracks, and so on.

When it's time to recreate the original tape:

1. Record the original drum track first.

2. Cue up the next two tracks, and set up to record only the non‑drum track, but monitor both tracks.

3. Cue up DAT and ADAT to the beginning of the tune, with the DAT in pause mode.

4. Start ADAT a bit before the beginning, then at the precise moment the tune begins, start the DAT.

If you're lucky, the two will start in sync (as evidenced by the drum tracks flanging instead of giving a slapback echo effect). If there's a bit of a slapback echo, don't sweat it for relatively unrhythmic parts like vocals. Otherwise, try again until it syncs.

Make sure you extend the drum part about 15 to 30 seconds before the beginning of the tune (but mute this for a few seconds just before the song begins). If you record this 'pre‑roll' drum part on the DAT, and the DAT and ADAT parts don't sync up properly at first, you can fiddle with ADAT's variable speed control to slow down or speed up until ADAT catches up with the DAT. With any luck, the two will be 'synched' before the tune's actual beginning.