title: PCM audio amplitude values?
body: <p>I am starting out with audio recording using my Android smartphone.</p>
  
  <p>I successfully saved voice recordings to a PCM file. When I parse the data and print out the signed, 16-bit values, I can create a graph like the one below. <strong>However, I do not understand the amplitude values along the y-axis.</strong> </p>
  
  <ol>
  <li><p>What exactly are the units for the amplitude values? The values are signed 16-bit, so they must range from -32K to +32K. But what do these values represent? Decibels? </p></li>
  <li><p>If I use 8-bit values, then the values must range from -128 to +128. How would that get mapped to the volume/"loudness" of the 16-bit values? Would you just use a 16-to-1 quantisation mapping?</p></li>
  <li><p>Why are there negative values? I would think that complete silence would result in values of 0.</p></li>
  </ol>
  
  <p>If someone can point me to a website with information on what's being recorded, I would appreciate it. I found <a href="https://ccrma.stanford.edu/courses/422/projects/WaveFormat/" rel="noreferrer">webpages</a> on the PCM file format, but not what the data values are.</p>
  
  <p><img src="https://i.stack.imgur.com/W6SL8.png" alt="enter image description here"></p>