I'm thinking of buying the Rode, but wonder how to ensure its noise is above the USB interface I use - TASCAM US 122.
More math:
The Rode NT1A sensitivity of -32dBV/Pa, less its SNR of 88dB is -120dBV noise floor.
Compare to the Tascam--well, here we go, ambiguous specs. Preamp manufacturers do that all the time. To me, a proper noise spec clearly states equivalent input noise. Tascam states "dynamic range and signal to noise ratio" for the mic input to insert send as ">100dB". OK . . . as we know dynamic range is supposed to be maximum level to noise floor, and signal to noise ratio is nominal level to noise floor. The insert send max level is stated as +6dBV, and the nominal level as -10dBV. If we take the max level as the reference, that's an appalling -94dBV noise floor. I don't believe that, so let's assume they really meant 100dB SNR and 116dB dynamic range (yes, 116dB is more than 100dB, but that's still a lazy way to quote a spec). -10dBV nominal level less 100dB SNR is -110dBV, or 10dB noisier than the Rode.
This isn't terribly surprising as Rode prides themselves on extreme low noise, and a low-end USB interface is bound to be somewhat noisy. Note however that Tascam spec'ed noise at minimum gain, which is bold because noise is usually relatively worse at low gain (contrary to popular belief). It's just that no one really cares about noise at low gain, because low gain means you have a really hot signal. So maybe the higher gain settings are quieter.
One thing that Tascam is kinda trying to bury under the rug is the noise performance of its converter, which they state as 93dB. That's a 16 bit dynamic range--or is that the SNR, with some digital "headroom"? I have no idea, thanks to their somewhat obtuse specs. Maybe it's really 109dB dynamic range, who knows?
Does it matter to you? If you are doing nature recordings, probably. You will compromise the noise performance of the Rode when recording bird chirps or something. For rock music, it won't matter much. Acoustic music . . . you may or may not notice, it's hard to say.