Not all phones produce great audio quality, but Xiaomi phones actually give you a fair amount of options without having to download a third party app to boost audio performance.
If you are suffering from poor audio quality with your Mi device, try the following:
Turn on Settings –> Sound & Vibration –> Audio settings –> Mi sound Enhancer (image above).
When possible, match the current earphones you are using with those on the list.
If your earphones are not on the list, go through the list and try them all, there might be one that sounds great with the earphones you have, even though they do not match one earphones selected.
You can also try manually adjusting the Equalizer, if you feel like tweaking the settings.