I would agree with most of the people here that the difference between 16 bit and 24 bit audio is usually difficult to hear, but there is another side to this debate that no one has mentioned yet: the mathematical side. As you all should know, digital audio is made up of two elements, sample rate and quantization, where sample rate is the time element and quantization is the amplitude element. Also, you all should know that the bit word of a digital audio is the mathematical means by which a series of amplitudes is encoded; each instantaneous voltage is assigned a binary value in the form [x1, x2, x3, ... , xn] where the values of x are obviously either 0 or 1 and n is equal to the bit depth. Now, simple combinatorics will reveal the total number of possible amplitudes is equal to 2^n. By this formula, there are 65,536 different possible amplitudes in a 16 bit audio signal. By comparison, a 24 bit audio signal contains 16,777,216 possible amplitudes; this is 256 times the ammount of 16 bit. Now what does all of this mean to our ears? Dynamic range! It is a valid statment that 24 bit audio has 256 times greater dynamic range than 16 bit audio. While this may not be worth anything when faced with the task of recording an Eminem album, it can certainly come into play when recording more subltle acoustic material such as Jazz. Another aspect to considrer is the fact that DSP will be carried out more accurately on a 24 bit signal than it would be on 1 16 bit signal, which is likely why mastering engineers prefer the 24 bit format. My advice would be to let the source material be the deciding factor when debating 16 vs 24.