RME Fireface UCX II 40-Channel USB-B Audio/MIDI Interface - Manual (Page 43)

User's Guide Fireface UCX II © RME
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20.3 DC-coupled Outputs (CV/Gate)
All eight analog outputs of the UCX II are DC-coupled. AC coupling via capacitor is common,
both directly after the DAC chip and directly at the output socket. This prevents a fixed DC com-
ponent at the output, which could cause negative effects such as popping noise or malfunctions
in other devices that are also DC-coupled. However, it also serves as protection against danger-
ous DC from the outside.
DC coupling has the obvious advantage of allowing the output to operate level-linearly down to 0
Hz. Even at extremely low bass (16 Hz) phase shifts are avoided. DC-coupled inputs are rare,
especially for power amplifiers, so a possible DC offset of a playback normally does not cause
serious issues.
In order to realize the outputs stable and reliable (robust) as DC-coupled, the circuitry was de-
signed for low DC-offsets and sufficient overvoltage protection. That this works has been proven
for years, not only by RME's ADI series.
To be able to generate DC is quite useful in measurement technology, also in connection with
audio. However, DC coupling is especially desirable in combination with analog, electronic
sound generators (synthesizers). These have an input that can control the pitch as well as other
functions via a DC voltage. Control Voltage, short CV, often also CV/Gate (gate determines tone
on or off), CV Filter etc. is mostly based on the voltage range 0 to +5 Volt. If an audio interface
can output such DC voltages then synthesizers can be controlled via suitable software and the
analog outputs of the audio interface.
The DA converters and analog output stages used in the UCX II have a very low DC drift and
generate the DC voltages very reliably and reproducibly, so they are very well suited for this ap-
plication.
Polarity - Phase
Since the outputs (of course) have a correct polarity, and TotalMix fully supports DC (via fader
and level meter), a positive voltage appears at the analog output when a digital positive DC is
played. The amount of voltage can be measured accurately and directly with any cheap multime-
ter.
Negative output voltages should be avoided, because they could theoretically lead to defects
in the CV input. Even if the software used generates only positive signals, a simple phase
inversion in TotalMix can invert the signal so that a negative voltage is send out.
Voltage Ranges
Line Out 1-6 , unbalanced (mono jack), unloaded:
+19 dBu: +9.5 V, +13 dBu: +4.75 V, +4 dBu: +1.7 V
Phones 7/8 , unbalanced, unloaded:
High (+19 dBu): +9.5 V, Low (+4 dBu): +1.7 V
Note: The level meters in TotalMix show DC 3 dB higher due to its factory default setting. This
can be changed by disabling the
Settings - Level Meters - RMS +3 dB option in TotalMix FX.