This folder contains the VUMeters application. This application measures the sound level at the input and output of the DSP (Digital Signal Processing) sections of the Macintosh AV computers. Use it to verify that you have sound connected to the sound input of the Macintosh AV computers. This application *should* work with any DSP card that runs the Apple Real Time Architecture (ARTA).
This application was written to test ideas about analog levels in a digital world. The concept of VUMeters is familiar to anybody who has used a tape deck. VU means Volume Unit and the precise definition of a VU meter's behaviour can be found in an article by Chinn, Gannett, and Morris in the Bell System Technical Journal of January 1940 (volume 19, pp 94-137.)
This implementation of a VUMeter can be used to monitor the input or output of the DSP Standard Sound System. Four viewing modes are possible: left, right, both channels, or the maximum of the two channels. Each meter can be set to display the maximum digital level or the analog power level. The maximum levels are useful because they make it easy to verify that the signal does not exceed the maximum level that can be handled by the digital system. The analog power level readings are more conventional. The VUMeters measure the sound level compared to a reference. The two references that are implemented in this application are analog (1 milliwatt into 600 ohms) or digital (how close to saturating the A/D and D/A converters.) Finally, the meters can be set to either respond instantenously or to simulte the mechanical meters.
Normally this application needs the DSP hardware and software installed (these are standard with the Macintosh Centris 660AV and Quadra 840AV computers.)
There is a special test mode if you would like to test this application without the DSP hardware and software. When double clicking on the application, hold down the option key until the first window appears on the screen. Then the meter's level will be tied to the movement of the mouse. Left/Right motion is hooked to the meter's left channel, while up/down movement is connected to the right channel.
This software is copyright 1992-1993 by Apple Computer, Inc. You may use this software and distribute it without charges. Feel free to study the enclosed code as an example of DSP programming on the Macintosh. Show it to all your friends to demonstrate how cool the Macintosh is and we'll all be happy.
