pre-emphasis filter - parameter a
Hope this is right...
$$h[n]=\delta[n]-a\delta[n-1]$$
$$H(e^{jw})= 1- ae^{-jw} =(1-a\cos(\omega))+ja\sin(\omega)$$
$$|H(e^{j\omega})|= \sqrt{1 + a^2 -2a\cos(\omega)}$$
$$DB_\omega \triangleq 20\log(|H(e^{j\omega})|)$$
$$20\log((1 + a^2 -2a\cos(\omega))^{1/2})= DB_\omega$$
$$1 + a^2 -2a\cos(\omega)= 10^{DB_\omega/10}$$
$$a^2 -2a\cos(\omega) +1-10^{DB_\omega/10}=0$$

with $\omega = 2 \pi \frac{2100}{10000}, \ DB_\omega=1.343 \ \Rightarrow \ a \in \{0.9, -0.4026\}$

$a = -0.4026$ results in a low-pass pre-emphasis whereas $a = 0.9$ results in a high-pass pre-emphasis.