Universal Audio DCS-RP Manual - Manual (Page 14)

9
Matching Pre Outputs to DAW inputs
The GAIN Trim feature is uniquely designed to allow users to match the DCS Remote Preamp's outputs to the inputs
of a wide range of DAW audio interfaces. When a typical outboard preamp is used with a DAW, the user must
carefully watch the on-screen meters while adjusting preamp gain in order to get the signal hot enough for best A/D
conversion while making sure it's not clipping the DAW's maximum input or 0dBFS. This is difficult to do if the user is
trying to set the preamp gain from a remote location where the on-screen meters can't easily be seen. In many cases
a typical preamp's gain and trim may be set so that the preamp clips before the DAW input which results in an
unwanted clipped recording. Or the opposite case may occur when a hi-output preamp has to have it's gain backed
way down to avoid clipping the input of a USB or FireWire interface - resulting in a recording that has more preamp
noise buried in the recorded signal.
Correctly setting the GAIN Trim will eliminate both of the common problems mentioned above. Look up the max input
level (dBu RMS) of the audio interface and set the GAIN Trim to the same max dBu number. Once this is done, the
user may adjust preamp gain without needing to see the on-screen meters while knowing the gain structure is
optimized to get the best signal quality out of the preamp and the DAW audio interface.
The DCS Remote Preamp is similar to audio interface A/D converters in that the signal quality gets better as it nears
the maximum output level - at which point it clips. GAIN Trim provides a simple method to help users to match the
max preamp output level (peak clip) to the DAW max input level (0dBFS clip). The published maximum input levels of
several popular interfaces are listed below:
Digidesign Mbox (1)
+13 dBu RME Multiface +3/+13/+19 dBu
Digidesign Mbox 2 +21 dBu RME Fireface 800 +2/+13/+19 dBu
Digidesign 002 & 002R +18 dBu (switch settings)
M-audio Fast Track Pro +4 dBu E-mu 1820M +20 dBu
M-audio Delta 1010 +20 dBu Tascam US-122 +20 dBu
M-Audio Delta 66 +14dBu Tascam FW-1804 +20 dBu
M-audio Project Mix I/O +10 dBu Mackie Spike +22dBu
M-Audio Audiophile 192 +14.2dBu
MOTU
Traveler +18dBu Presonus Firepod +18dBu
MOTU 828mk2 +18dBu Presonus Firebox +18dBu
MOTUUltraLite +18dBu
MOTU 2408mk3 +18dBu
NOTE: When setting GAIN Trim
in the range from 19 to 24 dBu, balanced cabling must be used between the Pre
Outputs and the downstream device. For settings between 0 and 18 dBu, either balanced or unbalanced cabling
may be used. If unbalanced cabling is used with GAIN Trim
settings greater than +18, the Preamp will
automatically detect the fault condition and reset GAIN Trim to +18. When the RP resets the GAIN trim, it will
flash the peak clip leds and GAIN trim button to let you know GAIN Trim has been reset to +18.
Phase Inversion
The need for preamp phase inversion is best shown by a common example - recording an open-backed guitar
amplifier with 2 microphones. The first mic is placed close to the front of the amp's speaker. When recording to a
computer-based system, the wave-form displays an upward peak when the speaker pushes outward (positive)
sound pressure on the mic. When a second mic is added near the back of the amp, its recorded wave-form shows a
downward (negative) valley when the speaker pushes forward - from the back of the amp the speaker moves away
from the mic, creating negative sound pressure. If these 2 signals are mixed (see Remote Preamp A+B mode), the
positive wave-form from the front mic combines with the negative wave-form from the back mic to result in
cancellation of much of the amp's sound and a "thinning effect" that is usually disappointing. But, if the phase of
the amp-back mic signal is inverted, the 2 signals will now combine instead of cancel, and the result will usually be
pleasing and useful. Other double-mic applications requiring this method include piano soundboards, drum heads,
and guitar tops (mics inside and outside soundhole).