SoundTuner

SoundTuner is a Chrome extension that gives you precise control over background audio on every tab. Core features include Gain (up to 5x), Pan for left-right balance, and Mono to normalize across channels, helping when audio is too loud, too soft, or only audible in one ear.

It also saves audio settings per domain or per page and loads them when you open a new tab, so you don't have to reconfigure each time. For questions and source code, visit the GitHub repository linked in the extension description.