Record Enable; Setting Levels - Alesis ADAT-XT20 Reference Manual

R
ECORD
To record enable a track, press the track's RECORD ENABLE button.
When you press a track's RECORD ENABLE button for the first time, the
track's red REC LED will flash, indicating the track is in record-ready, and its
INPUT LED will light (unless Auto Input is on and the transport is in play),
indicating you will be able to monitor that track's input. If the transport is put
into record mode (see Transport Controls in this chapter), recording will begin
on this track; the track's REC LED will stop flashing and remain lit. To disable
record-ready, press the track's RECORD ENABLE button once again. The
track's REC LED will turn off.
RECORD ENABLE buttons can be turned on or off while you are in record mode.
S
ETTING
Unlike analog tape recorders, where signals routinely exceed 0 dB with no
apparent ill effects, 0 dB on the XT20 represents the maximum possible signal
level. Signals above 0 dB will be clipped and lead to digital distortion.
Because of the limitations of analog tape, there was always a tradeoff between
noise, level and distortion. More level improved the signal-to-noise ratio, but
also increased distortion. This distortion increased linearly, which is why
signal-to-noise was often specified for a certain amount of distortion (typically
3%). You could always record with hotter levels or softer levels, but either
more distortion or more noise would result—with analog, you couldn't have low
noise, high levels and low distortion.
With digital recording, there is a much wider dynamic range, and distortion
does not increase with increasing level. Yet once a digital system runs out of
headroom and hits 0 dB, that's it—the onset of distortion is immediate and
very noticeable if the signal is sustained several dB above the limit. Even
though very short peaks above 0 may not last long enough to cause audible
distortion, you aren't capturing the signal in its original form. As a result,
because of the XT20's signal to noise characteristics, it's better to err on the side
of setting levels not quite high enough rather than having them distort,
especially during live recording when you don't get a second chance. In the
studio, where you have more control over levels or are using compressor/
limiters, it's OK to light up the MAX LED on the meter on the very loudest
peaks, as long as you're sure that signals aren't going beyond that point (by
using the meters on your console, if they go beyond +15 dB).
However, since 0 dB on the XT20 equals the maximum level, the input reference
level is set below 0 VU. With the XT20, a 0 VU signal on a +4 dBu mixer
plugged into the XT20's +4 dBu connectors (or a 0 VU signal on a -10 dBV mixer
plugged into the XT20's -10 dBV connectors) will register -15 dB (the first green
segment) on the XT20's meters. Therefore, you can run the mixer over 0 VU and
ADAT XT20 Reference Manual
E
NABLE
L
EVELS
Basic Operations: Chapter 4
65