this is pretty interesting:
http://www.postunder.com/files/minimag/sep04/kicks.html
..."More Tips" from the page above:
When desgining your kick using any of the above methods, you will find that playing with the amplitude and pitch envelopes produce various variations, for instance a tight volume envelope will produce a sound resembling the "909" kick, while a more loose envelope with a longer decay will produce the sustaining low end "oomph" charactaristic of "808" kicks.
To further improve your kick sounds equalization and compresion come in handy. With an equalizer one basic concept would be to trim much of the mid andhigh frequencies and leave only a small "spike" or "snap" higher freqency for some character in the kick's attack. Then proceed to trim some of the "muddy" bass areas. Usually this falls around 150-250 or so hz. Even if you don't hear it, your kick may contain very low bass frequencies (around 30-40hz and less) that even really good monitors have problems reproducing. Also, because you don't hear them reproduced on your speakers these frequencies can often be very loud and cause many sound related problems such as digital clipping and a constant attempt by your monitors to deal with these frequencies. To avoid this it is especialy important on bass sounds to trim all frequencies below a certain threshold. Trim at least below 20hz, if not up to 40.
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this might be a nice read too:
Memoid's kickdrum tutorial
http://www.energyuk.net/music/produc...amp;criteria=*