Sound Devices USBPre 2 - Manual (Page 17)

USBPre 2 User Guide and Technical Information
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Features and specifications are subject to change. Visit www.sounddevices.com for the latest documentation.
Linux Installation and Connection
The USBPre 2 is an Audio Device Class USB standard peripheral. No proprietary drivers are re-
quired to operate the USBPre 2 under Linux. The fi rst time the USBPre 2 is plugged in, Linux will
enable standard USB Audio Device Class drivers automatically (if necesarry).
Current Linux audio drivers only support USB audio devices at “Full speed” USB rates. The USBPre
2 must be forced into Full Speed mode by holding down the Input 1 Source button when plugging in
the USB cable to the USBPre 2.
Before connecting the USBPre 2, quit all open applications that use audio. An application that is
running when the USBPre 2 is connected may not recognize the USBPre 2 until the application is
restarted.
Inputs
Input Source Selection
The USBPre 2 has two available input channels. The source for each input is independently selected
using the Input Select Buttons on the front panel. The selected source is indicated by an illuminated
LED next to the respective Input Select Button. The Input Select Buttons can be locked to prevent ac-
cidental switching of the input sources.
See DIP Switch Options .
Microphone Inputs
Phantom Power
The USBPre 2 provides 48-volt phantom power for condenser microphones connected to the XLR
inputs. Phantom power can be engaged independently for each input.
See DIP Switch Options . Con-
denser microphones that can operate on phantom voltages from 11-52 volts will function properly
with 48-volt phantom.
Dynamic microphones typically do not require phantom power. A properly connected balanced,
dynamic microphone is not affected by the presence of phantom power nor will it draw any current.
However, it is good practice to turn phantom power off when not needed. Poor or incorrectly wired
microphone cable can cause audible artifacts in microphone signals. Some wireless receivers outputs
are adversely affected by the presence of phantom power, therefore, consult the wireless receiver
documentation.
Low-Cut Filter
The low-cut fi lter attenuates low frequency signals. This is useful in conditions where low frequency
signal is causing overload before the desired gain is reached (windy environments or handheld mi-
crophones, for example).
Input Pad
With some combinations of microphone sensitivity and sound pressure levels, the microphone input
of the USBPre 2 can become overloaded even when the input gain is at its lowest level. A 15 dB pad
can be engaged on the microphone input to reduce its sensitivity.
See DIP Switch Options .
Input Limiters
In environments where high sound pressure levels may occur unexpectedly, input limiting prevents
distortion by attenuating signals that surpass the input threshold level. In normal operation with
properly set input levels, the threshold of an input limiter is rarely reached. Signals below the thresh-
old are not affected by the limiter. Limiters can be engaged on each microphone input independently.
See DIP Switch Options . The amber LIM LED’s on the right side of the meters will illuminate to indi-
cate when limiting is occurring.