Electrical – What will the output voltage be of an audio usb converter/dac

universal protocol that is used by the likes of USB audio

Sounds like the USB Audio Class specification.

Is this conversion from output of ADC to USB data stream something which we can do, say, with a microcontroller?

Some USB microcontrollers - NXP LPC17xx for example - have example code for USB Audio Class available.

Audio inputs are usually capacitively coupled. This means low frequencies are attenuated and DC, the lowest frequency of all, is blocked entirely. Usually audio circuits are designed such that low means something around the lower limit of human hearing, about 20 Hz.

A typical audio input stage might look like this:

^{simulate this circuit – Schematic created using CircuitLab}

C1 serves to block any DC. The parallel combination of R1 and R2 set the input impedance. You can also view this arrangement as a simple low-pass RC filter, with the RC time constant, and thus the cutoff frequency of the filter, defined by R1||R2 and C1.

R1 and R2 meanwhile create a voltage divider that set the DC level as seen by the ADC or whatever follows. Usually R1 and R2 will be equal so that the DC level is midway between the supply rails, to allow for maximum voltage swing in either direction.