https://www.cnet.com/news/alexa-crank-the-bass-amazon-rolls-out-equalizer-controls-for-echo-devices/

Audiophiles love to nitpick over the way their music sounds, but until now, you haven't been able to do that with any of Amazon's Echo smart speakers. I say "until now" because starting this week, Echo users will be able to tweak the treble, mid-range or bass on their smart speaker by opening the Alexa app, or by simply asking Alexa herself (provided of course that she can hear, something Alexa sometimes struggles with during music playback).

To do so, just use a command like, "Alexa, set treble to maximum," or "Alexa, decrease the mid-range," or "Alexa, turn up the bass." You can adjust each setting on a scale from -6 dB to 6 dB (e.g., "Alexa, set the treble to minus three"), and when you do so, the new sound settings will apply across all playback -- music, podcasts, audiobooks, you name it. If things sound wonky, you can always go back to the default mix by saying, "Alexa, reset equalizer."