Between units? You'd have to put up sound board.

Sound can be a real pain to manage and to cut it out entirely can be an expensive process.

A few cheap fixes however can be to make sure your walls are insulated properly and, if that doesn't work, adding sound board or another layer of drywall, stuck to the first with green glue, and then fixed with drywall screws.

Remember, bass builds up in corners, so building out soffits, or even using statues or plants in the corners of rooms can help diffuse sound waves.

Good luck!

Thanks.