The processor Obviously, multitrack audio applications demand a lot of CPU horsepower. Your PC will not only be your multitrack recorder, it will be your mixing console, too, your FX rack, and with the new software synths, it will act as an array of musical instruments - all this at the same time and in real time. And it will make a lot of colorful pictures on the screen while doing all this. If I look a mere 5 years back, I am truly amazed. We've come a long way, baby.
Audio processing demands a lot of floating point operations.
This is what you are always told by software manufacturers. Keep in mind that for the processor, handling integer numbers is fundamentally different from handling floating point numbers. Floating point numbers can be handled much faster by modern processors. Now the audio applications work with floating point numbers which gives them a better resolution for the audio data. Why this is so would take another article altogether which I might post sometime if there's demand.