<font color='#000000'>ALPHA 24 is essentially an upsampler. Basically it processes 16 bit PCM and increases it to 24 bits. It doesn't truly add 'real' information, but is supposes to do a more accurate job of reproducing the information present.
Denon's claim is that it produces smoother, more 'analog' sound. I haven't heard it myself, but Micheal Fremer (of Stereophile & SGHT) has said it's effective.</font>