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Chapter 5 Input/Output Interfaces
5.8 AUDIO SUBSYSTEM
This system includes an embedded Sound Blaster-compatible audio subsystem with front panel-
accessible headphone and microphone jacks.
5.8.1 FUNCTIONAL ANALYSIS
A block diagram of the audio subsystem is shown in Figure 5-10. These systems use the AC’97
Audio Controller of the MCP component to access and control an Analog Devices AD1885 or
AD1981B Audio Codec, which provides the analog-to-digital (ADC) and digital-to-analog (DAC)
conversions as well as the mixing functions. All control functions such as volume, audio source
selection, and sampling rate are controlled through software over the PCI bus through the AC97
Audio Controller of the MCP component. Control data and digital audio streams (record and
playback) are transferred between the Audio Controller and the Audio Codec over the AC97 Link
Bus.
This system incorporates Business Audio, which has the codec stereo analog output applied
through headphone jacks and switch logic to a mono 3-watt amplifier that drives a 16-ohm
speaker. The switch logic allows the system to provide headphone functionality with or without
the front panel assembly installed.
The analog interfaces allowing connection to external audio devices include:
Mic In - This input uses a three-conductor (stereo) mini-jack that is specifically designed for
connection of a condenser microphone with an impedance of 10-K ohms. This is the default
recording input after a system reset. Either the front or rear panel microphone jack is available for
use (but not simultaneously).
Line In - This input uses a three-conductor (stereo) mini-jack that is specifically designed for
connection of a high-impedance (10k-ohm) audio source such as a tape deck.
Headphones Out - This input uses a three-conductor (stereo) mini-jack that is designed for
connecting a set of 16-ohm (nom.) stereo headphones or powered speakers. Plugging into the
Headphones jack mutes the signal to the internal speaker.
Line Out - This output uses a three-conductor (stereo) mini-jack for connecting left and right
channel line-level signals (20-K ohm impedance). A typical connection would be to a tape
recorder’s Line In (Record In) jacks, an amplifier’s Line In jacks, or to powered speakers that
contain amplifiers. Plugging into the Line Out mutes the internal speaker.
5-26 Compaq D315 and hp d325 Personal Computers
Featuring the AMD Athlon XP Processor
Second Edition – April 2003