Chapter 6 Audio Subsystem
Compaq Deskpro EN Series of Personal Computers
Desktop and Minitower Form Factors
Third Edition - September 1998
6-2
6.2 FUNCTIONAL DESCRIPTION
A block diagram of the audio subsystem is shown in Figure 6-1. The architecture is based on the
ES1869 audio controller that provides the ADC, DAC, FM synthesis, spatializer 3D audio, and
mixing functions. The audio output is processed though a six-level equalizer designed to
compensate for chassis acoustics. A 5-watt low-distortion amplifier (TDA7056A) drives a long-
excursion speaker for optimum sound. All audio functions are controlled by software. The
software volume control uses 6-bit resolution providing 64 levels.
In addition to the connections provided for CD-ROM, four analog interfaces are provided to
connect to external audio devices and are discussed in the following paragraphs.
Line In - This input 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 tuner’s
Line Out or Record Out jacks, or to a tape deck’s Line Out or Playback Output jacks. A less
optimum but acceptable connection would be to the h eadphone output of th e t a pe deck or CD
player.
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 or Record In jacks, to an amplifier’s Line I n jacks, or to “powered” compu ter
speakers that contain amplifiers. Plugging into the Line Out mutes the internal speaker.
Mic In - This input uses a three-conductor (stereo) mini-jack that is specifically designed for
connecting a condenser microphone with an impedance of 1-K ohms. This is the default
recording input after a system reset.
Headphone Out - This output uses a three-conductor (stereo) mini-jack for connecting a pair of
stereo headphones with a minimum impedance of 16 ohms. This jack can also be used to connect
a pair of un-powered or powered speakers of the type designed to be used with portable
radio/cassette/CD players). Using this connector defeats (mutes) the internal speaker and Line
Out signals.