Design of an Audio Multitone Refiner, Simulation of Audio Frequencies & Analysis Using Active Filter

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Chapter 3. DESIGN:
The approach exploited here was rigorous and experimentation coupled with, mathematical analysis, programming/ computation- to -simply calculations-, circuit synthesis and simulation or modeling (see special comments below) with Butterworth filter response as the favourite standard in this study; however, multiple feedback band pass (MFB) Filter would be used (approximate) unit- gain frequency bandwidth.
Special Comment: the design package used here is limited in applications in that while it allowed some features to be exploited; it disallowed (subscript) others hence Vin (wherever it is seen in this write-up implies) Vi, likewise Va=Va R1=R1, R2=R2, R3=R3, C1=C1, C2=C2, and C3=C3. These were adhered to in the subsequent chapters expect in some cases where circuit models were properly drawn.
The input low frequency response signal needs to be defined. It is done once through C1 and Rin; to prevent a very saggy bottom end to the frequency response that might result using non inverting as the input a single series capacitor C1 and the bias resistor ( the equivalent op-amp input resistance ) parallel resonant together to limit the passable or allowable feed in frequency. While for the inverting type, there is series resonant between series C1 and a series input resistor R1, 3Db down at 5Hz, and 0.2Db down at 20Hz, which is definitely inside the audio band. The op-amp were so guided to ensure stable dc biasing round all its terminal hence high pass at about (5Hz) were placed the op-amp to steer tract its dc bias while that along the supplies were to maintain stability at high frequency and to filter distortion frequency in the supplies lines. Once the starting frequency 15Hz 'the necessary octave division and quality factor, Q to use for various frequencies bands had been determined, other frequencies could be factor, taken a crucial reference to main vocal frequencies using the expression : [...].
3.1 Filter Architecture:
The