Multiple Channels of Sound
One of the most useful enhancements made to the Sound Manager is the ability to have multiple channels of sampled sound produce output on the
Macintosh audio hardware con currently. Previous versions of the
Sound Manager could play only a single channel of sampled sound at a time. One consequence of this was that if a system alert sound was called while a
sampled sound was playing, the alert sound would not be heard (although, if
you were lucky, the menu bar might flash). A more important consequence was
that it was impossible to provide the layering of sound that can bring a touch of
reality to a simulation or presentation. Furthermore, the limitation to one
sampled sound at a time made it very difficult for an application to incorporate
Macintosh- synthesized voice output with any other kind of
Macintosh-generated sound.
Using the enhanced Sound Manager, your application can open several channels of sampled sound for concurrent output on the available audio
hardware. Similarly, multiple applications can each open channels of sampled
sound. The number and quality of concurrent channels of sound are limited only
by the abilities of the machine, particularly by the speed of the CPU. Different
Macintosh computers have different CPU clock speeds and execute in structions
at quite different rates. This means that some machines can manage more
channels of sound and produce higher-quality sound than other machines. For
example, a Macintosh II may be able to support several channels of
high-quality stereo sound without significant impact on other processing,
whereas a Macintosh Plus is able to support only a single channel before other
processing slows significantly. The newly enhanced Sound Manager provides the capability to balance CPU loads for sound-related activity, thereby further
insulating the application from the underlying hardware.
only on machines equipped with an Apple Sound Chip. To maintain maximum
compatibility between machines for your applications, you should always
check the operating environment (using the Gestalt function documented in channels of sampled sound is present before attempting to do so.