M-AUDIO Duo USB - Manual (Page 13)

Phantom Power
Unlike dynamic microphones, many "condenser microphones" need to receive a
DC voltage (generally 48v) from an external source before they can generate an
output signal. If the condenser mic doesn’t come with its own power supply, then
phantom power must be applied from the pre-amp. Pressing the "Phantom
Power" button and engaging phantom power on the Duo will send the necessary
voltage to BOTH of the XLR Mic Inputs.
Phantom power will not affect a dynamic mic adversely, so its okay to have a
dynamic mic at the XLR input while phantom power is switched on. Just to be
safe, check you mic’s documentation to see if it will accept or needs phantom
power. Some ribbon mics definitely should NOT receive phantom power, as this
could damage them.
Using the Pad Switch
On the front panel of the Duo, a “Pad” Switch is provided to attenuate a signal
that is too hot before it gets to the mic preamp. If you find that your signal tends
to clip even when the gain control knobs are set extremely low, try engaging the
Pad Switch.
When pressed and locked to the in position, the corresponding signal will be trimmed
by 20dB. Gain reduction is bypassed when this switch is in the out position.
Standalone Mode
The Duo can also be used in a “Standalone” mode, independent of your
computer. Pressing the “Standalone” switch on the front panel and locking it to
the in position will connect the input channels, Channel 1 and Channel 2, directly
to the Line Out, S/PDIF Out, and Headphone Out of the Duo.
Operating the Duo in Standalone mode will give you three options:
1. The Duo can be used as an analog to digital, or “A/D” converter. A signal
present at either the Mic Inputs or the Line Inputs will be converted to a
digital audio signal and sent to the S/PDIF Out on the Duo. This will allow
the Duo to be used with another digital audio device that accepts a S/PDIF
signal, and not as a digital audio interface in conjunction with your computer.
2. The Duo can be used as a microphone preamp, again, independent of your
computer. A signal at the Mic Inputs of the Duo will appear at the Line Outs,
allowing you to use the Duo’s mic preamp in a sound reinforcement situation
or similar instance where its use as a computer interface is not necessary.
3. A “direct monitoring” capability can be achieved when Standalone mode is
engaged while the Duo is in use as a digital audio interface in conjunction with
your computer. This will give you zero latency monitoring of the signals present
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