Ask questions about keyboard control latency

For more information about keyboard control latency-Linux general technology-Linux programming and kernel, see the following. I suddenly wanted to play the piano, but the piano was too expensive. it was not something that I could do without any business, so I planned to compile a software for playing the piano on my computer, in Windows, I know I already have it, but I only have linux. There is a flash software for playing the piano, but only one click can ring at a time, cannot control the value of the notes. Think of racing games before, as long as the direction key is not loose, the car can keep moving forward, so I think, programming should have a function to read the key time. There is also dos. there is a function in h that can control the tone by reading the audio frequency, but I can't find this header file. I searched it and said it was a function in turbo C, which is also related to DOS, linux may not be available

Now let's talk about the problems I want to solve:
Tone Control function
The function that controls the time by holding down the keyboard