Krook wrote:should i get baslline samples and use the 16 levels or eq the original sample and remove the highs...... are they're any other alternatives?
Alternatives all day, but that's the beauty of this stuff. The two things you mentioned are basic places to start. On the 16 levels you only can stretch one sample so far though. Filtering/EQ-ing a melody sample and leaving the low frequency content as you mentioned is the tried and true "Low End Theory" going back to the late 80's. Doing that you can also get away with lowering the filtered sample with the bass a half or full octave which sometime really thickens things up.
Then you also could use VST's and multisampled patches. With mulisampled basses you avoid the limitation of pitching one sound using the 16 levels and can have the full range of notes and expressive playing with the full range of a stringed or synth bass. Find the root key of your melody, and make bass in that key and your off.
And then there's the old but forever valid technique of just loading a sine wav and using some envelopes/filtering and modulation to get that in the mix. A lot of old school hip hop was done that way. Bomb Squad/PE were really big on a sine wav in an Akai S rack sampler. But it's great how all the old techniques still can be used even in software.