Keep your peaks well below 0 dB. Without this "oxygen," mastering tools will cause distortion and clipping.
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If you're listening to your favorite mixes on platforms like Spotify, you can make the experience more professional:
Go track-by-track and cut frequencies that don't contribute to the overall sound. Use high-pass filters on everything except bass elements to clean up the mud.
It is the primary version that usually appears first on a release package.