How to write a code that can take input from a hardware?

Question

I want to take a signal input from the line in jack of my computer and then by using some fixed frequency values, i want to print some alphabets for those fixed values. exactly what do i need to do to connect the hardware with my software. so i need to use some specific language???

Answer 1

Drivers are what provide this, not 100% sure what the exported interface of a sound card driver will be like although id imagine you could get that information by calls to the driver.If not you may have to write your own driver(fun).

I'd advise C/C++

Answer 2

Assuming Linux, you need to simply read data from /dev/dsp .  C or C++ would probably be your best choice.  You'll probably need to call an FFT function to convert the A/D data to frequencies.  There should be plenty of free FFT libraries for Linux in C or C++.  Of course, you could do the time sensitive stuff in C, and the rest of the work in a higher level language.