Digital recording is very different from analogue when it comes to setting the right recording level. Jerry Halatyn helps you to understand your DAT machine...
So you finally went out and bought a DAT machine! You probably couldn't wait to plug it in, turn it on and record music with a purity previously impossible with your budget. You probably thought you'd breeze through the owner's manual and get right down to some serious digital recording in no time. How hard could it be? Connect the inputs and outputs, set the record level and... hang on — what kind of meter is this? No values above 0dB? No nominal level?
You quickly learn, through trial and error, that if you go over 0dB on a DAT machine, the result is nasty distortion or complete muting of the signal (depending upon the model you own). You suddenly have to think of your levels as existing within a margin below 0dB — a new way of thinking for many of us!
So where should your average level be? Eventually you learn that there isn't really an industry standard by which you can set DAT recording levels — it seems that everyone has their own way of doing it.
The most common advice given is simply to record as hot as possible — without going over 0dB. Using this method, you might find yourself constantly adjusting the record level, reducing it gradually after having overloaded the DAT machine several times. Just when you think you've got it right, the slightest change in the mix sends the meter over the top. In this case, a compressor can help balance the dynamics within the music. Since a smooth, subtle effect is desirable, a soft‑knee compressor will yield the best results. A limiter is also effective but should be used as a kind of insurance policy to help keep those few highest peaks in check. Be sure to avoid 'crunching' the signal down to fit on the DAT.
The 'as hot as possible' approach does take advantage of the DAT machine's dynamic range, which is, at best, about 96dB (a little better than two‑thirds of what the human ear can handle). However, it does not regard the dynamics of the recorded music, and this may lead to another problem.
Take, for example, the following scenario: you've just mixed down two songs. During playback, you notice that the mellow song (Song A) sounds louder than the more lively one (Song B). Neither mix went over 0dB — so why is one louder than the other? Because a song with relatively narrow dynamics, when recorded as hot as possible, has an average signal level that sits higher on the meter, closer to 0dB while never going over it. This can make it sound twice as loud as a more energetic song whose transient peaks keep its average signal level several dBs lower.
The problem of relative levels arises because our ears perceive sound based on average level, while a DAT machine's meters read peak levels to warn of clipping. Because of this it isn't practical to set a notional point on the meter that will work for every song, as every song has a different peak‑to‑average ratio. It is possible to balance the subjective levels of successive mixes on a DAT tape by making aural judgements of apparent loudness, but for this to really work, the song with the highest peak‑to‑average energy ratio needs to come first, so that the other mixes can be referenced to that.
An alternative is to compress the songs that have wide peak‑to‑average ratios, but only if the compression doesn't compromise the way the song sounds. Because most DAT masters destined for album release are re‑compiled on some form of editing system, it is generally safer to leave level‑matching until that stage, which means that you can go for maximum level on every track you mix.
Headroom is the safety margin between the level you think you'll need and the point at which the signal level hits the endstops. Because you can't always predict the level of the highest peak, it is essential to leave some headroom, but this may vary with the type of music you are recording. For example, a dance track may have a limited dynamic range, so you could get away with something like 12dB of headroom above the average signal level. However, it's the peaks that matter as far as the DAT machine is concerned, so keep an eye on them. More dynamic music may need to be recorded with even greater headroom, but the trickiest situation is in live recording; even if you've done a trial run, the levels may change significantly for the actual performance. In this case, you could set your nominal recording level around 20dB below clipping, just to be on the safe side. This will, theoretically, compromise the signal quality to some extent, but because of the wide dynamic range of DAT, this is unlikely to be serious, and is far better than audible clipping.
It is common practice to match the nominal level of a mixing console's L/R outputs with a specific level on the DAT machine (usually, anywhere between ‑20dB and ‑12dB, depending upon the required headroom). This allows the engineer to concentrate on the console's L/R meters while occasionally checking the DAT machine's levels.
To align a DAT machine to your desk:
- First determine the headroom you'll require (let's say you've chosen 14dB).
- Next, generate a 1kHz reference tone which registers 0VU on your desk's L/R meter.
- Turn down the DAT machine's record level and put it into REC/PAUSE mode.
- Turn up the record level slowly until the DAT machine's meter reads ‑14dB.
- With the machines aligned, you simply refer to your desk's L/R meters while recording. Keep the average level around 0VU, which now corresponds to ‑14dB (your virtual nominal level) on the DAT machine.
Whatever you choose as your nominal level on DAT, it's a good idea to record a reference tone at that level. This is quite helpful when calibrating your console's 2‑track returns or aligning other recorders for dubbing copies from the DAT machine.
As usual with audio recording, there are few rules and many guidelines for setting DAT levels. Whichever method you use, remember this: anything you record will have some sort of dynamics, including peaks, as well as an average level. For the best results, establish an appropriate headroom and, of course, never go over 0dB or else ... (MUTE)