I'm going to listen to your song while I reply...
1. Yes, please try to sit up straight. Think about moving the drums and cymbals instead of your body. I obsessed for a while about the optimum height for my drum stool to create the optimum angle for my legs to play the kick drum. I also bought longer drumsticks when I realized that I was holding my sticks past the end of the stick. Ergonomics is important in all things.
2. You have to "mix" yourself when playing the drums. Kick and Snare are the loudest elements, then the toms, and lastly the cymbals. I'm sure you can find tricks to help cut down the level of high hat, but the best thing you can do is just practice playing the high hats as lightly as possible while playing the kick and snare as loud as possible. Additionally, smaller darker high hats seem to be less of an issue.
3. Check to see if your kick drum legs have spikes on the ends and dig them into your floor. If your drums are on a carpet and the whole carpet is moving forward try to get as much of the carpet under your stool to weigh it down. Again, I suggest keeping the kit on a bare floor, but if it isn't an option you could always put something heavy in front of it. When I tracked drums in my old bed room, I would put the kick drum against the futon. Not only did it keep it from sliding, but the futon absorbed some of the excess low end frequencies.
4. Can you record three mics at once? If you can only use two mics, Use the Beta 58 on the kick and the Nady as an over head. I think your real problem with the snare is tuning and playing. Does it sound good to in the room when you play it? Wimpy = weak. Hit the drum harder. If you can record a third mic, once you get the other two mics sounding good alone and together, add the Tascam as a snare mic. Position it about two inches above the rim of the snare, about two inches back, under the high hat, point down towards the center of the snare. This is not much of an angle, and you should be hitting the snare in the middle. If not, point the mic where you are hitting the drum. If you want more attack (head sound) point the mic closer to the edge of the drum. Another technique that might work well with this mic is to mic the shell of the drum on the side. This gives more body than attack or snare, but sometimes sounds nice.
5. You can improve your groove by playing simply and practicing with a metronome. I find that just playing a straight four, (Kick - snare - kick -snare) is tough for a lot of casual drummers. This simple drum beat can be incredibly powerful if played with precision and authority. If you can make this groove you have the foundation for more complicated beats.
I also suspect your overhead mic is too high. Try it at head height or lower next time. You really have to use your ears, have someone play the kit while you listen. If you don't have a drum playing accomplice, record and check. Spend some time just moving the mic up and down, left and right to see what happens. For BSS, I have a small diaphragm condenser almost at cymbal height as close to the center of the kit as possible pointed mainly toward the snare.
I really like this article by Andy Hong on recording drums at home:
http://www.kimcheerecords.com/articles/drums/
Good luck!
Ken
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