The compression of speech signals has many practical applications. One example is in digital cellular technology where many users share the same frequency bandwidth. Compression allows more users to share the system than otherwise possible. For a given memory size, compression allows longer messages to be stored than otherwise.
Further compression is possible at a cost of lower quality.
The rate at which the vocal cords vibrate determines the pitch of your voice. The shape of your vocal tract determines the sound that you make. As you speak, your vocal tract changes its shape producing different sound. The amount of air coming from your lung determines the loudness of your voice. The above model is often called the LPC Model.