Apple 17-INCH Sound Outputs, Built-in Microphone, Audio Input Jack, Modem Activity Sound Signals

CHAPTER 3

Devices and Ports

Built-in Microphone

The built-in microphone is located at the bottom of the left speaker grill.

The sound signal from the built-in microphone goes through a dedicated preamplifier that raises its nominal 30 mV level to a nominal 150 mV (peak-to-peak) signal to the sound circuitry. That signal level assures good quality digitizing without driving the analog input into clipping.

Audio Input Jack

The audio input jack is a 3.5 mm mini phone jack that accepts line-level stereo signals. It also accepts a stereo miniplug-to-RCA cable adapter for connecting stereo equipment to the computer.

The sound input jack signal connections are

●tip: audio left channel

●ring: audio right channel

●sleeve: audio ground

Modem Activity Sound Signals

Modem activity sound signals from the communications slot are sent to the Snapper sound circuitry as 8-bit digital data.

Sound Outputs

The sound system sends sound output signals to the built-in speakers and the external sound output jack.

Headphone Jack

The headphone jack is located on the left side of the computer. The headphone jack provides enough current to drive a pair of low-impedance headphones. It can also be used as a line-level output.

The headphone jack has the following electrical characteristics:

●impedance suitable for driving standard 32-ohm headphones

●output level 2.0 V peak-to-peak (1.41 V RMS)

●signal-to-noise (SNR) 90 dB unweighted (typical)

●total harmonic distortion (THD) 0.03% or less

50Sound System

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