Date: Fri, 14 Apr 2000 20:26:37 +0200

Author: Urs Lauterburg

Subject: Re: Microphones and Power Macs

Post:

LeRoy,

I have actually done quite a bit of audio recording with the standard Apple
Plain Talk microphone to investigate signal properties in the audio range.
Although the microphone is certainly not the most expensive one I think its
performance is not really bad. However I don't know what the microphone's
specifications really look like. I think you should be able to find plenty
of microphones for better sound acquisition but the good ones are not cheap
and you will need a preamplifier to get a mike with proper signal gain
check with a local music- or Apple store for wiring compatibility.

Below a snipped from The Apple TIL archives about the G3 sound port specs.

If you need specific help do not hesitate to ask.

Have fun and enjoy physics at its best.

Urs

Urs Lauterburg
Physics Edutainer
University of Bern
Switzerland

Apple sound prort information:

TOPIC
What are the sound capabilities of the Power Macintosh G3?


DISCUSSION
The Power Macintosh G3 is not configured as a typical AV style Power
Macintosh in that it does not have RCA jacks for sound in and out, nor
additional video in and out ports. Instead is relies on external FireWire
devices for providing advanced audio/video capabilites.

Here are the details relating to the sound capabilities of the Power
Macintosh G3 logic board:

Sound System
The sound system for the Power Macintosh G3 computer supports 44.1 kHz
16-bit stereo sound output and input, available simultaneously.

Like other AV class Macintosh computers, the sound circuitry and system
software can create sounds digitally and either play the sounds through
speaker inside the enclosure or send the sound signals out through the
sound output jack. The Power Macintosh G3 computer also records sound from
several sources: an analog sound source connected to the line-level sound
input jack, analog sound from the modem card connected to the internal
modem connector, or a compact disc in the CD-ROM player. With each sound
input source, sound playthrough can be enabled or disabled.

Sound Output
The Power Macintosh G3 computer provides one 3.5-mm mini jack for sound
output on the back of the enclosure. The output jack is connected to the
sound amplifier; the mini jack is intended for connecting a pair of
headphones or amplified external speakers. Inserting a plug into the sound
output mini jack disconnects the internal speaker. The enclosure has one
built-in speaker.

The Burgundy IC provides the stereo sound output to both the internal
speakers and the sound output jack. The sound output jack has the following
electrical characteristics:
* output sound signal to noise ratio (SNR) <90 dB unweighted (typical) when
sound playback is from
system hard disk drive or main memory
* output sound SNR <80 dB unweighted (nominal) when playback is from CD
* overall output sound SNR <90 dB unweighted (typical)

Sound Input
The Power Macintosh G3 computer provides a stereo sound input jack on the
back of the enclosure for connecting an external PlainTalk microphone or
other sound source. The sound input jack accepts a standard 3.5-mm
stereophonic phone plug (two signals plus ground).

Note: The Apple PlainTalk microphone requires power from the main computer,
which it obtains by way of an extra-long, 4-conductor plug that makes
contact with a 5-volt pin inside the sound input jack.

The sound input jack has the following electrical characteristics:
* input impedance: 20 kOhm
* maximum input level without distortion: 2.5 V peak to peak (Vpp) maximum
* line-level microphone voltage range of 0.28 V to 2.1 V peak to peak
* input SNR <90 dB unweighted (typical) for recording to system hard disk
drive or system main
memory

Digitizing Sound
The sound circuitry digitizes and records sound as 44.1 kHz 16-bit samples.
If a sound sampled at a lower rate on another computer is played as output,
the Sound Manager transparently upsamples the sound to 44.1 kHz prior to
outputting the audio to the Burgundy sound IC.

The preferred sound sampling rate for output is specified in the Monitors
and Sound control panel when the sound input is not in use. The preferred
output sampling rate is overridden by the
setting of the input sampling rate, because the input and output sampling
rates are physically locked together. The sound output sampling rate is
always 44.1 kHz.

When recording sound from a microphone, applications that are concerned
about feedback should disable sound playthrough by calling the Sound
Manager APIs.

The Burgundy IC provides separate sound buffers for input and for stereo
output so that the computer can record and send digitized sound to the
sound outputs simultaneously.

Burgundy Sound IC

The Burgundy custom IC combines a waveform amplifier with an internal
18-bit digital sound codec (only 16 bits supported for analog to
digital/digital to analog sound capture and playback). The Burgundy IC
supports all of the audio input and output features on the DVD-Video and
Audio/Video Card. The Burgundy IC provides improved audio performance over
the Screamer IC used on the Audio/Video and Audio input/output cards.

The Burgundy sound IC combines a 16-bit digital sound encoder and decoder
(codec). The Burgundy IC has the following sound controller features:

Digitizes analog inputs with internal analog to digital converters (A/Ds).
Creates analog outputs with internal digital to analog converters (DACs).
Facilitates digital audio routing between the inputs and outputs and CPU.
Provides digital gain, fade, balance, and mute controls.
Provides digital tone control.

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