I'm a guitarist but I'm going to buy a bass guitar so I can record some tracks and I was wondering if I would need a 4 or 5 string bass to match my tuning

Well a 5 string would be helpful since standard tuning already has the low B.

You COULD tune a 4 string to a B tuning but I don't imagine the tension would be great, unless you bought a 5 string set and used the low B from that set instead of using just a heavy gauge 4 string set.
If you are heavily into down-tuning, then go with a five-string. It will definitely make things easier.
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Not technically a bass owner yet (pending), but a 5-string just offered more flexibility. I downtune my guitars and run a 7-string in standard tuning, so it made sense to go with a 5. I'm used to a wider neck, and the 5's I've tried out have been comfortable (Ibanez SR305, Yamaha TRBX305, Schecter Stiletto, Sterling 5). For the record, I have a Stiletto coming in this week, but if you're comfortable with a wider neck, I can't see why a 5'er would be a bad thing. Try some out; I recommend Yamaha or Schecter for starters.
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justinguitar.com is the answer
I would go with a 5 string. But when you say you're recording songs in B standard I assume you mean you're using a 6 string guitar tuned down to B standard? (BEADGB). I think that is what you're saying, which makes it a fairly clear choice you should get a 5 string.
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