Acoustics: Reflection and Transmission Coefficients

While studying about reflections and transmission coefficient in a discontinuous Media I came across two definition of coefficients one which seems to be correct according to me as it is in accordance with the physics but there is another definition which I have found in many books and used in many papers. Consider a case, when wave is incident from low impedance medium 1 to high impedance medium 2. Then as per my understanding, the amplitude of incident wave should decrease as it goes from low to high impedance ( given by relation 2 below). But if I use relation 1, the amplitude of transmitted wave increases as we go from low to high impedance and that is not possible.

$Z_1$ and $Z_2$ are impedance of two media

• Relation 1:

$$R= \frac{Z_2 - Z_1}{Z_1 + Z_2},\quad T = \frac{2 Z_2}{Z_1 + Z_2}$$

• Relation 2: $$R = \frac{Z_1 - Z_2}{Z_1 + Z_2},\quad T = \frac{2 Z_1}{Z1 + Z_2}$$

Could someone please clarify my doubts and discrepancy in the relations that I found?

Reference

1. Kinsler. Fundamentals of Acoustics.