Like the title says, the audio gets dropped by about 70% any time their is a sound in another app. This lasts for a few seconds. Very irritating. A problem with Spotify specifically, doesn't seem happen with others apps.
You may choose a preset from the presets list on the right, or set the levels on your own. When the “EQ Enabled” box is ticked, the equalizer is active and all sounds from all streams are affected by the its settings.