do u've any idea of signal and system,if not then use openhaim's book,
Added after 22 minutes:
if u've idea about signal n system then u can use following books
1: digital signal processing by S Salivahanan.
2: Signal processing by B.P lathi
3: u can download dsp guide from dspguide.com,its free
4:for computer based approch u can use sanjev k mitra's book
5: discrete time signal processing by openhaim