Be careful by just saying it takes xx db of sound pressure to mask your T. It really depends on the spectral content of the noise. If you have 13khz T it is a lot harder to mask than 1khz because of the frequency spectrum of the noise sources. Download an app like Decible X and look at the FFT of various environments and you will see what I mean. Most places have higher amplitude low frequency noise than higher. I'm just saying this isn't a good metric to compare with. Rather it would be better to figure out high how on the fft the adjacent frequencies need to be to mask the T. This would give a better idea of the overall volume of the T.