I think you are using the wrong tool for the job. Semitones are spaced logarithmically but FIR filters have linear frequency resolution. If you want to reliably distinguish between the low E and the low F on the bass guitar you need a frequency resolution of better than 2 Hz which requires 10s of thousands of taps (at 48 kHz sample rate).
That's why most audio processing is using IIR filters. There are various options to explore:
Standard IIR bandpass: Butterworth, etc. An interesting one to try out would be a Chebysheff Type 2 filter were you put the first zero of the stop band right on the neighboring semitone to notch it out.
Here is an example of a 5th order Cheby2 filter centered at 220 Hz (A3) with the first zeros in the neighboring semitones.
Once you have something you like you can use the same design parameters for any other tone frequency, the design just "warps" but maintains it's overall shape.
It will be MUCH cheaper to implement than an equivalent FIR filter and work even at very low frequency, although it will get fairly sluggish.
Standard Biquads. You could try a peaking filter with a very high Q at the center frequency plus two notches at the neighboring semitones. This may take a little tweaking to get it to look good.
Heterodyne. Multiply the input signal with cosine of the center frequency and then apply a low pass filter with the desired bandwidth. This will turn a bandpass problem into a similar lowpass problem. You still need to design a different lowpass for each note, but you can control the bandwidth directly.
As with all filter design problem it's extremely important to get the requirements right. Filter design requires a lot of trade off so the better you understand which properties are important to your application, the better the filter will be: Passband ripple, transition steepness, stopband attenuation, group delay, phase distortion, complexity, MIPS and memory, latency, numerical noise, etc.
Especially at low frequency you will have to trade off frequency resolution vs group delay (which will VERY high), latency and tracking speed.