power(2,12)=4096 bits
power(2,14)=16384 bits
difference = 12288 bits
It comes down to alliasing , and how well the digital conversion represents the analog signal. Obviously 14 bit is a lot better than 12 bit.
The link below explains the idea of aliasing -
http://www.dsptutor.freeuk.com/aliasing/AD102.html
This might illustrate the advantage of 14 bit cf 12 bit :
http://www.earthboundlight.com/photo...us-12-bit.html