What Are The Semantics Of Wav-File Sample Values?
I don't know much about this semantics? of WAV files but their numerical format is the following. (assuming mono) 


Given a recording with 8-bit per sample precision, then those samples are unsigned integers taking values between $0$ and $255$. Due to being unsigned, to represent negative values,  there is a bias of $128$, and the sample values are actually interpreted to be between $-128$ and $127$. In this case a value of $128$ represents silence, maximum value $255$ corresponds to an input full scale positive audio waveform and $0$ represents neagitve full scale input waveform.
For $16$-bit WAV files, you have $16$-bit signed integers that range from $-32768$ to $32767$ and $0$ represents silence. Again, $32767$ represents full scale audio input without scaling.


Note that here I refer to a microphone recording through an ADC system which converts analog audio input in the standard range of about $1$ V rms into WAV samples. Please check this 1-V rms for being something higher, about 1.5 Volts or else depending on particular implementation or some specific audio standard. In any case, the analog circuitry is responsible for transmitting a full scale audio to the ADC whan a 1V (or 1.5V) rms wave is present at the input and then the conversion is performed according to the above setting when WAV recording is performed.