WAV encoding problem
The PCM values are proportional to the sound pressure. 8-bit PCM is stored with an offset of 128, so PCM coded values from 0 to 255 code for 'pressure values' from -128 to 127.
These values are often normalized to the range -1.0..+1.0.
The PCM values are linear representation of the sound pressure, and a log operation is only required if you want to express the sound pressure in decibels.
To get actual sound pressure levels in Pascal or dB(A) you would need a calibrated .wav signal.