audio signal sampled data processing

How do I do operations on audio signal sampled data? For ex. I want to double the amplitude of audio data(multiply the data by 2)

[Walter Roberson]

Double to relative amplitude? Or double the pressure?

[RoboKid]

double the pressure

[Walter Roberson]

The back of my memory is saying that pressure is proportional to amplitude squared; if so then multiply by sqrt(2). I could easily be wrong on the relationship.