Digital audio equalizers emerged in

Digital audio equalizers emerged in the late 1970s and early 1980s [19–22], leading to commercialdeployment in Yamaha’s 1987 DEQ7 Digital Equalizer, the first DSP-based parametric equalizer. Ayear later, Roland rolled out its variable digital equalizer, the E-660. Around the same time, importantdigital equalizer designs appeared: White published design formulas for digital biquadratic equalizingfilters [23], and Regalia and Mitra proposed a useful allpass-filter based structure for digital shelvingand parametric equalizing filters [24]. Both of these groundbreaking works are based on discretizationof analog prototypes. Since then, there has been a proliferation of advances and improvements,including the octave and 1/3-octave graphic equalizer, constant-Q (bandwidth) graphic equalizers,and many other advances discussed throughout this paper.