1) you need an amplifier
2) no you need to bias the input waveform to 2.5V
Even for a desktop computer microphone?
Is that like mixing 2.5V with my audio signal?
If so, can I just put both in the same pin,
Use 10K pull up and pull down on the analogue input
and couple the audio in with a none polerised capacitor as big as you have got.
How that capacitor goes here? Between the signal and the input pin
Non-polarized capacitor of which type?
I don't know how long takes writting a byte to a file in a SD card.
Will the technique discussed in this thread work too?
No idea, the url is wrong.
Copy and past normally works for me. Just put the link into url tags and don't use the link icon.
Another technique is to put a pin high, do the code and put it low, using port manipulation.
Then measure the width of the pulse on an oscilloscope.
Will the "port manipulation" execute almost instantly?
Will a cheapy one work too?