u have to know the tempo to ur sample.. otherwise u wont get the best results...it doesnt matter if ur using pp or timestretch or semitones and cents for getting the sample to fit u have to know the tempo of ur sample..if ur sample is smaller than a measure say 2 beats then multiply ur samples lentgh 2 times to make it 4 beats then break out the deepsound calculator
http://mp3.deepsound.net/eng/samples_calculs.php
this calculator owns and whoever wrote the tempo detect in akais mpc1000 should get fired.. just to save ur self from headaches when u sample make sure to have atleast a measure long sample to work with for tempo reasons.. once u get a tempo for a measure long sample u can divide ur sample in half and just keep the boom and bap.. theres no real way of sampling im just giving u my tips. most people here dont use loops for space reasons.. u only got 128mb in ur box so use it wisely....
i like to add that somtimes ull have to make ur sample 2 measures long just to avoid the retardness of the robotic sound in timestretch but remember after u timestretch cut off the excess skin of the sample..u dont need boom bam over and over and over agin..unless u wanna work with loops