This chapter has focused on virtual analog effects. These digital audio effects are implemented using modern methods, but the aim is to reproduce historical sonorities. In this chapter we have described simulations for various analog filters, tube amplifiers, plate and spring reverberation, tape echo, and an old telephone. Time-domain processing techniques have been applied in all cases. One reason for this is that many algorithms contain nonlinear elements: thus the processing depends on instantaneous sample values and must proceed sample by sample. The nonlinearities, which imitate the behavior of analog components, bring about pleasing distortion and compression, familiar characteristics of nostalgic music equipment.
1 https://ccrma.stanford.edu/∼jos/filters/Quality_Factor_Q.html
2 http://faust.grame.fr/
3 https://ccrma.stanford.edu/∼jos/filters/Analog_Allpass_Filters.html
4 https://ccrma.stanford.edu/∼jos/pasp/Bilinear_Transformation.html
5 As an aside, note that if the distance between the record head and the playback head were equal to integer multiples of the capstan and pinch-wheel circumferences, the quasi-periodic time delay trajectory components would be eliminated.