Here is a great guide to show you where the different frequency ranges are so you can make better choices when mixing your track. Feel Free to book mark this post as reference when mixing!
Muddiness can be rolled off around 300Hz. Add a small boost around 5-8kHz to add some high end to punch through the mix.
50-100Hz Adds bottom to the sound
100-250Hz Adds roundness
250-800Hz Muddiness Area
5-8kHz Adds high end presence
8-12kHz Adds Hiss
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