Audio Equalizer
Add-on

https://mybrowseraddon.com/audio-equalizer.html
If you’re a little unhappy with the sound quality of your speakers or headphones when listening to streamed music, podcasts, videos, etc on the web and were considering buying something different, try this add-on before you do. I’d also suggest this might be useful for those who are neurodivergent and sensitive to certain sound frequencies, eg a like or dislike of those tones and notes in the higher or lower frequencies.
Created by Muyor, it’s available for Chrome, Firefox and Opera browsers and works with any website that uses HTML5 audio or video elements. It’s free and provides a nice lightweight console with a number of presets or you can set your own preferences for 10 individual frequency ranges from 32Hz to 16KHz. So if those high or low tones are too much, use this to cut them out. Likewise if your speakers or headphones are sounding a bit flat or too biased towards certain frequencies, it’s worthwhile giving this at least a try.
I was prompted to write something about this add-on after noticing a marked improvement in the sound quality from streamed videos and music websites.
It does not detect what audio device you have connected, so if you switch from headphones to speakers or vice versa you may find you have to quickly switch from one saved setting to another, but the interface is easily accessible and user-friendly.