User's Manual - Cornell Lab of Ornithology - Cornell University

Appendix F Using the Macintosh Built-inSound Input PortAbout the Macintosh built-in sound input portAs of this writing (August 1995), two different types of sound input port are available onMacintosh computers. Both types are marked with a small microphone icon and accept a stereominiplug (1/8” phone plug). However, the two types of input port are wired differently.WARNING!Before you connect any sound input device other than the microphone that came with thecomputer, it is critical that you determine which type of sound input port your Macintoshhas. Connecting audio equipment (e.g., a tape recorder, CD player, or stereo system) to thesound input port incorrectly may damage the audio equipment and/or the computer!Determining the type of the sound input portThe simplest way to tell which type of sound input port a Macintosh has is to examine themicrophone that came with the machine. The “classic” sound input port is found on Mac models(including the Mac LC, Mac IIsi and non-AV Quadras) that come with a disc-shaped AppleOmni-Directional Microphone that is about 3.5 cm (1.5 inches) in diameter. These models acceptonly one channel of input sound. The “PlainTalk” sound input port is used on Macintosh models(including AV Macs and PowerMacs) that come with an Apple PlainTalk Microphone, which isroughly triangular in shape and about 5 cm (2 inches) wide. The PlainTalk sound input portsupports two input channels (stereo).Line input to a “classic” Macintosh sound input portAlthough it is possible to connect a line output cable directly from an audio device to the classicsound input port using a stereo (three-conductor) miniplug or adapter, doing so may yielddistorted signals and may damage the audio device, because the wiring of the classic port doesnot conform to standard conventions for stereo mini-plugs. Use of a mono (two-conductor) miniplugin the classic port may damage the computer.Problem: Distortion of the digitized signalThe classic port is designed for a mic level input voltage. However, standard audio line levelsignals (such as those produced from the Line Out jack of a tape recorder or CD player) are muchhigher. A line level signal can saturate the Mac’s digitizer, resulting in severely distorted signals.Problem: Damage to audio devices and the MacintoshA stereo mini-plug has three contacts: a tip contact, a barrel contact, and a ring contact (betweenthe tip and the barrel). A mono miniplug has only a tip and barrel contact. In most audioCanary 1.2 User’s Manual 229