Calibration
The following sections provide a more detailed look at some of the aspects of recording
studio setup and trouble-shooting. While it is not absolutely necessary to read the
material we feel that a basic understanding of the principles of calibration, equipment
interface, and grounding issues can go a long way to helping engineers
before
the going
gets rough. If one encounters inconsistent levels or hum problems in the studio, the
following hints may help in understanding the issues and resolving the problems. These
issues apply to recording gear in general, not just the 2Bus LT.
The Dangerous 2Bus LT comes to you fully calibrated and ready to hook up. In order to
enjoy the full benefits of a 2Bus LT system, the D/As used with it should be aligned. This
can be done with the aid of a Voltmeter (VU meter in a compressor or other piece of gear
on hand) and the digital oscillator found as a plug-in in most DAW systems. While it is
not necessary to align the system, better and more consistent mix results will be obtained
if this is done. There are two analog operating levels that most digital recording systems
have converged upon depending on whether the situation is for
recording
or
mastering
.
The difference between the two worlds is whether the maximum electrical stress is
imposed by
amplitude
limiting (recording) or
slew-rate
limiting (mastering).
Professional recording systems in the US have historically used the VU meter for
system alignment and level monitoring, so naturally, with many years of precedent, there
are holdovers today from that system (derived from the telephone and broadcast
industries). The standard of ‘0VU’ comes from the Bell Telephone engineers needing a
convenient way to measure signal levels in phone lines and switching systems. 600 ohm
balanced lines were the norm and 1 milliwatt of energy was a pertinent amount of juice
moving through phone circuits. A ‘building out’ resistor was added to the VU meter to
avoid loading the audio circuit down and the reference level cranked back up so the meter
read ‘0VU’. The resulting standard level wound up at +4dBu, or roughly 1.23 volts AC
RMS. This standard has been with us for more than 60 years now the world over and is
the ‘reference level’ to which most professional audio systems are aligned.
Alignment Chart
Volts AC
VU
dBu
dBfs (recording)
dBfs (mastering)
9.76 v
Tilt
+22
0 (full scale)
Tilt
6.16 v
Tilt
+18
-4dBfs
0
(full
scale)
1.23 v
0
VU
+4dBu
-18dBfs -14dBfs
-5-
