Hola:
AudioBus lets you load up several apps at the same time and easily switch between them. It simplifies making things work together. Now support MIDI, and doesn't host a certain kind of app called Audio Unit Extensions (abbreviated various ways around here ... AU, AUX, etc). It also allows you to save the "state" of your setup, which captures the apps and most of the settings they're using to easily recall later.
AUM supplements that by providing mixing, audio routing, some MIDI management, and an easy way to record audio output. It also hosts AU's, which is significant.
La principal diferencia es que AUM soporta el formato AU, puedes mezclar las diferentes señales, puedes enviarlas a diferentes salidas, graba y reproduce audio.
Saludos.
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