M-audio Duo USB User Manual download pdf (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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M-audio Duo USB User Manual Page 13