Dangerous Music 2-Bus - Manual (Page 6)

Dangerous Music 2-Bus Manual
6
A/D converters in a recording situation are usually set to have a +22dBu maximum input
level to achieve full scale. This allows for occasional loud hits to not clip the converter.
D/A’s for this system would typically be aligned to have unity gain with the A/D’s. This
is done by running a -18dBfs signal at 1 kHz with the digital oscillator to the individual
D/A outputs one channel at a time. Turn the 2-Bus output gain knob all the way up and
measure the voltage across pins 2 and 3 of the 2-Bus output connector. If there is a device
in the studio that has a calibrated VU meter (Dangerous MQ, tape machine, compressor)
patching the 2-Bus into it makes for convenient adjustment. Set the D/A converter gain
so that the volume indicator reads 0 VU or 1.23 volts AC on the voltmeter.
After the D/A’s are aligned, the A/D’s are aligned by using the oscillator and one
of the D/A’s as a source. Feed that signal into the A/D’s one at a time and meter it in the
DAW. Adjust the A/D for -18dB full scale. Once all the converters are aligned, the
system becomes easier to handle because there is a wonderful consistency from channel
to channel. This makes cross patching and bussing assignment seamless.
Mastering systems are typically calibrated at -14dB from full scale for a
maximum analog signal level of +18dBu. The reason for this is because mastered signals
tend to be compressed and bright. There is a lot of rapid change (slew-rate) in the signal
that overloads processing gear and converters before the amplitude gets up to +22dBu.
Some savvy 2-Bus users set their D/A converters as if they were mastering to be
able to take full advantage of the dynamic range such a calibrated system has to offer. In
other words, A/D’s are set to avoid clipping for recording and D/A’s are set to avoid
overloading the mixdown converter. This is done by aligning one D/A at -18dBfs and
using it to calibrate the A/D’s as above. Then set the all the D/A’s so that -14dB full scale
is 0VU by running the digital oscillator at -14dB and adjusting the D/A output levels to
read 1.23 volts AC or 0VU. This allows one to run the stems at hot levels without
overloading the mixdown A/D converter.
Grounding and Interface
In order to achieve maximum performance of any recording system, the cables need to be
wired properly. Following are diagrams of frequently encountered wiring scenarios to
help explain some of the possibilities. We’ll start with professional, balanced, +4dBu
levels encountered in most studio systems and then cover some contingencies that happen
when interfacing -10dBV, unbalanced systems. Understanding this next bit is the key to
quiet, reliable, and consistent studio operation.
The balanced world is the easiest to deal with because the audio signals and the
shield are kept separate down the interconnect cables. Properly wired systems with
balanced interfaces can achieve impressive signal to noise ratios with the least amount of
bother. Unbalanced equipment (RCA connectors or _” connectors with tip/sleeve) can be
made to perform well but can be more bother because the signal reference voltage (the
low side or ground) and the cable shield are one and the same, unbalanced connections
having only 2 conductors in the cable. This sharing of signal and ground can cause
trouble because stray ground currents become the reference for the audio signal. This
situation can manifest itself as hum or buzzing sounds coming from the speakers and can
be remedied with some tinkering and jumper placement. The 2-Bus is designed to make
both types of connections easy and painless if some simple suggestions are followed.