This might help a little:
A typical sound card has:
a digital signal processor (DSP) that handles most computations
a digital to analog converter (DAC) for audio leaving the computer
an analog-to-digital converter (ADC) for audio coming into the computer
read-only memory (ROM) or Flash memory for storing data
musical instrument digital interface (MIDI) for connecting to external music
equipment (for many cards, the game port is also used to connect an external MIDI adapter)
jacks for connecting speakers and microphones, as well as line in and line out
on older ones a game port for connecting a joystick or gamepad
WAAAY back in the day I had a friend that wrote some of the first sound blaster drivers, I was his guinea pig to test them out on my PC that we built for me to use in College.