The loudness channel maps a data variable to how loud a sound is (or volume). Erie.js compiles loudness as gain, instead of physical volume that is measured in decibel because doing so may override or conflict with the user’s volume setting. For instance, a user with low hearing may have to set their device volumen higher than others, and a user with sensitive hearing may have set it lower than others. In addition, sampled audio has its own default volume, so controling them is nearly impossible. Instead, Erie Web Player maps the loudness to the gain (or velocity) of a sound (i.e., how strong a sound is played; or the amplitude of a sound), so that it works with users’ different volume settings (i.e., relative volume control). It’s always the very listener who has the control to the actual volume.

The unit of loudness/gain is from 0 to infinity, where 0 means muted sound (the signal is flat) and 1 means the default volume. However, if a loudness value is beyond 1 or 2, the sound might be too loud all at sudden, so we set the default loudness range to [0, 1].

Using the loudness is pretty straightforward.

loudness usage pattern

{
  ...
  "encoding" : {
    "loudness": {
      "field": "Body Mass (g)",
      "type": "quantitative",
      "scale": {
        "doamin": [0, 7000], // optional
        "range": [0, 1] // opational
      }
    }
  }
  ...
}

let stream = new Erie.Stream();
...
stream.encoding.loudness.field("Body Mass (g)", "quantitative");
stream.encoding.loudness.scale("domain", [0, 7000]); // optinal
stream.encoding.loudness.scale("range", [0, 1]); // optional
...