TITLE
    PowerBook 3400: Sound Specifications
Article ID:
Created:
Modified: 		24038
6/6/97
8/28/97
TOPIC

    What are the sound capabilities of the PowerBook 3400?

DISCUSSION

    Sound System
    The 16-bit stereo audio circuitry provides high-quality sound input and output through the built-in microphone and speakers. The user can also connect external input and output devices by way of the sound input and output jacks.

    The sound system is based on the AWAC codec IC along with input and output amplifiers and signal conditioners. In the PowerBook 3400 computer, the AWAC codec supports three channels of digital sound: two stereo channels plus a multiplexed channel. The sound system supports sample sizes up to 16 bits and sample rates of 11.025 kHz, 22.05 kHz, and 44.1 kHz.

    The frequency response of the sound circuits, not including the microphone and speakers, is within plus or minus 2 dB from 20 Hz to 20 kHz. Total harmonic distortion and noise is less than 0.05 percent with a 1-V rms sine wave input. The signal-to-noise ratio (SNR) is 85 dB, with no audible discrete tones.

    Note: All sound level specifications in this section are rms values.

    Sound Inputs
    The sound system accepts inputs from six possible sources:
    • built-in microphone
    • external sound input jack
    • sound from the PCI expansion slot
    • sound from the expansion bay
    • sound from a zoom video device in the lower PC card socket
    • 1-bit sound from the PC card sockets
    The microphone and the sound input jack have dedicated input channels on the AWAC IC; the other four inputs share a third input on the IC. Those four inputs are switched on and off by the hardware; they can be selected either as a group or in any combination for play-through or recording.

    Built-in Microphone
    The sound signal from the built-in microphone goes through a dedicated preamplifier that raises its nominal 30-mV level to the 1-V level of the codec circuits in the AWAC IC.

    External Sound Input
    The external sound input jack accepts a line-level signal or an Apple PlainTalk microphone. When a connector is plugged into the external sound input jack, the computer turns off the sound input from the built-in microphone. The input jack has the following electrical characteristics:
    • input impedance: 6.8k
    • maximum level: 2.0 V rms
    Note: The sound input jack accepts the maximum sound output of an audio CD without clipping. When working with sound sources that have significantly lower levels, you may wish to increase the signal gain of the sound input circuit. You can do that using the Sound Manager as described in Inside Macintosh in the Sound chapter.

    Expansion Bay Sound Input
    The sound input from the expansion bay has the following electrical characteristics:
    • input impedance: 3.2k
    • maximum level: 0.5 V rms
    PC Card Sound Input
    Each PC card socket has one sound output pin (SPKR_OUT) and the computer accepts either one or two cards. The one-bit digital signals from the sound output pins are exclusive-ORed together and routed to the built-in speaker and the external sound output jack.

    Sound Outputs
    The sound system sends computer-generated sounds or sounds from an expansion-bay device or PC card to the built-in speakers and to an external sound output jack. The sound output jack is located on the left side of the computer near the front.

    External Sound Output
    The sound output jack provides enough current to drive a pair of low-impedance headphones. The sound output jack has the following electrical characteristics:
    • output impedance: 33 ohms
    • minimum recommended load impedance: 32 ohms
    • maximum level: 1 V rms
    • maximum current: 32 mA peak
    Internal Speakers
    The computer has a total of four internal speakers: two 20 mm speakers located beneath the bezel between the back of the keyboard and the display, and two 50 mm speakers located in a tuned port enclosure in the back of the display. The 20 mm speakers are driven by the high-frequency portion of the stereo sound signals from the computer. The 50 mm speakers are driven by a monophonic mix of the low-frequency portion of the sound signals.

    The computer turns off the sound signals to the internal speaker when an external device is connected to the sound output jack and during power cycling.

    PCI Slot and Expansion Bay
    Sound output signals are provided at both the PCI slot and the expansion bay. The sound signals are line-level audio.


    This article was published in the 9 June 1997 "Information Alley".

Document Information
Product Area: Computers
Category: PowerBook
Sub Category: PowerBook 3000 Series

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