"Where does one get those big booming bass drum sounds so often heard in hip-hop recordings?"

Early on this was accomplished by using either (or both) a Roland TR-808 or TR-909 drum machine. These long ago discontinued models both have unique (and different) bass drum sounds that sustain in an interesting way. Being analog, they have a solidity to their low end that early digital drum machines lacked. Plus they can be easily tuned and still retain that solid sound quality. Even today tuned digital samples often lack the proper relationships of harmonics to sound "right" to our ears. With the proper tuning and EQ those sounds could shake a building if turned up loud enough. And that's just what early hip-hop artists were doing - spending all kinds of time tweaking EQ and compression settings - looking for that ideal sound just like we all do every day when we record. All kind of other techniques were introduced that added flavor to the sounds. Things like sine waves gated to the bass drum (a technique actually stolen from rock bands in the 1970's) and other bass sounds layered with the drum sounds all added more deep and sustained low end. Later those sounds were sampled and put into virtually every popular sampler library and PCM based synth and drum machine on the market, producing thousands of variations of those original themes, none of which ever really sounded exactly like the real thing. Nowadays there are a number of new analog rhythm machines and synthesizers that claim to be able to accurately produce these sounds, but of course some artists still prefer the original. At this point there have been so many variations of this type of sound recorded that "defining" it as one specific sound is impossible. Once again we're back in the subjective waters of what happens to work for the individual in context. If you're interested in this type of music, and the corresponding sounds, you do owe it to yourself to check out a real, original TR-808 or 909. You may find yourself sufficiently underwhelmed at the raw sound coming out of those machines that you'll be happy to use any of the popular drum machines or synths that have most of the processing done for you. On the other hand there's nothing quite like the original, if you know how to master it. Talk to your Sweetwater Sales Engineer for more help choosing a current instrument that will produce these sounds.