Appendix A. Ultimedia Services Audio Adapter

The Ultimedia Services Audio Adapter has four back panel connections. These include Microphone, Line In, Line Out, and Headphone. Each of these connections is implemented using a 3.5 mm (1/8 inch) stereo mini jack. Guidelines and requirements for each of these connections follow.

Note: Phantom power of .5 mA at 2 V DC for electret condenser microphones provided at both mini jack tip and ring.

Recommendations for microphone to be used with card:

• 600 ohms maximum impedance
• Cable length under 6 feet
• Open circuit voltage sensitivity greater than -80 dB (ref 1 V RMS per microbar). Typical: -40 dB
• Frequency response (frequency curve) depends on desired quality and application. Guidelines:

  Music applications: 20 Hz to 20 KHz, 3.5 dB, Speech applications: 50 Hz to 12 KHz, 5 dB

Suggested office speech microphone:

• Telex phantom power unidirectional electric condenser microphone, Telex part number 300262-0000.

Line In

2 V RMS (Input impedance: 30 K ohms typical).

Line Out

2 V RMS into 10 K ohms minimum.

Headphone

1.5 V RMS into 32 ohms.

Minimum impedance: 4 ohms.

The adapter provides two auxiliary input connectors. The first connector accepts 1 volt RMS nominal at an impedance of 50 K ohms, and it can be connected to a CD-ROM drive. The second auxiliary input connector is reserved for system use.

A mono microphone can be used to provide input to the mixer implemented on the adapter. The adapter also drives mono output to the Micro Channel audio summing node.