Kilobits Per Second = (kbps)
1,024 kilobits = 1 Megabit (Mb)
Recording time on 4GB:
32kbps ~ 280 hours
64kbps ~ 140 hours
128kbps ~ 70 hours
256kbps ~ 35 hours
An average song length of 4 minutes recorded at 128kbps takes up about 3.75MB of memory so a SanDisk 4GB SDHC Card can store 1000+ songs recorded at 128kbps.