DAFX: Digital Audio Effects, Second Edition

13.4 AM-DAFX Implementations

In this section we will describe the major steps needed to implement five different AM-DAFX. The resulting audio signal processing is the direct result of the analysis of the inter-relationship between input sources. The systems described are intended to be used for real-time signal processing. They can be implemented individually or cascaded together in order to implement an automatic audio mixer suitable for live audio mixing of music.

13.4.1 Source Enhancer

In audio mixing a common process is to enhance a source by making it more prominent. A way to achieve enhancement is by incrementing the gain of a source xμ(n) with respect of the other input sources. Performing such an action could introduce acoustic feedback or distortion if the gain needed is too large. For this reason the preferred action is to lower the gain of all sources, except for the one in need of enhancement. Although performing such an action will result in a stable enhancement of the desired source, it is not an optimal solution. This is because the sources that are not spectrally related to xμ(n) are also attenuated. In other words, if we aim to enhance a piccolo flute there should be no need to decrease a bass guitar because its spectral content shares little or no relationship with the piccolo. This type of complex frequency-dependent enhancement is familiar to audio engineers and it is what we aim to reproduce.

With this in mind we can design an AM-DAFX source enhancer whose ...