Hello, for Audio signal is pure analog processing, analog input and analog output. Di bale itong module ng vacuum tube pre-amplifier
standalone pre-amplifier na siya, kulang nalang ang Potentiometer para ma adjust ang Volume as a means to increase and decrease the Volume level. Iyong idea ay papalitan ng digital means (use Mciro Controller) inyong Potentiometer para mayroon ibat-ibang means of controlling the volume, puwede ito manual adjustment o di kaya puwede tin Remote Control IR o kaya RC, also to add stuff of displaying information to make the MMI to have a better interaction (Man Machine Interface), like when you increase the volume and you will see on the LCD the volume level in dB, or, when you go to the Menu and when you press it, you will hear a beep, some sort of.
So here, it is the idea of "controlling" that is why we have this digital module to do the job
The binary encoder, that looks like potentiometer but it generate binary signal which decode by the MCU, the program knows when you rotate left or rotate right or press the center to go into the Menu.
The yellow PCB composed the MCU and its hardware like Buzzer, Switch, LCD port, etc. which is the command center, this is where we load our program (firmware). Behind it is a Tone Control (green PCB), it is an analog process but the way it is controlled is digital means using the I2C protocol developed by Philips (NXP). It means, when you adjust any of its function like the Gain, Volume, Treble/Bass, you use program (I2C protocol).
We used this so that we can have a control of the Volume --- it is this reason we have more hardware, but it pays off with additional controlling and style, probably if you look at deeper into its electronics, maybe more degrade performance due to the fact that I2C protocol which is a high speed bit stream may interact into the analog processing which inject some sort of high frequency noise (when the design is not careful engineered). Those challenges makes diy builder a better guys, something they can be proud of when we (they) solved such problem on the power of their fingertips.