DAFX: Digital Audio Effects, Second Edition

10.4 Effects

In this section we introduce a set of effects and transformations that can be added to some of the analysis-synthesis frameworks that have just been presented. To do that we first need to change a few things on the implementations given above in order to make them suitable for incorporating the code for the transformations. We have to add new variables to handle the synthesis data and for controlling effects. Other modifications in the code are related to peak continuation and phase propagation. We first focus on the sinusoidal plus residual model, and next we will use the harmonic-based model.

10.4.1 Sinusoidal Plus Residual

In the implementation of the sinusoidal plus residual model presented, now we use different variables for analysis and synthesis parameters and keep a history of the last frame values. This is required for continuing analysis spectral peaks and propagating synthesis phases. The peak continuation implementation is really simple: each current frame peak is connected to the closest peak in frequency of the last frame. The phase propagation is also straightforward: it assumes that the frequency of connected peaks evolves linearly between consecutive frames. Note that when computing the residual we have to be careful to subtract the analysis sinusoids (not the synthesis ones) to the input signal. Another significant change is that here we use the parameter maxnS to limit the number of sinusoids. With that restriction, peaks found are sorted by energy ...