How to chose a kernel function for a FIR low pass filter in audio processing?
Yes the sinc kernel $$h[n] = \frac{\sin(\omega_c n)}{\pi n}$$ is the theoretical result for the ideal lowpass brickwall filter whose gain is one and cutoff frequency is $\omega_c$ radian per samples. 

Your filter impulse response will be samples of that function. Truncate it symmetrically to some finite length, and then apply a window on those samples. Windowing will help you achieve a much smoother response.