The Aphex Exciter is a Psycho Acoustic unit which tends to brighten up the sound of a recording, it is a subtle effect that has been available in a number of different versions over the years. Originally is was only available on hire, you could not buy it and paid by the hour.
I found this on the Internet "The Aphex Exciter is a tool that you can use to increase the presence and brightness of your audio signal. It does this by adding harmonic content to the signal, which can make it sound louder and more defined. There are a few different types of Aphex Exciters available, but they all do basically the same thing "
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