One of the best materials for sound insulation is mineral wool in quilt or batt form which can be stuffed between floor joists or stud work in your loft conversion.
Attic conversion ceiling joist loft framing.
You might open up your attic and find bare joists with fiberglass or cellulose insulation between the joists.
This means that new floor joists are fitted alongside them slightly raised above the ceiling plasterboard to avoid contact with it.
At least 50 of the usable area calculated above must have ceilings of at least 7 feet.
You can sister the joists by cutting 2 x8 boards the same length as the joists applying construction adhesive and affixing each to a joist with nails.
Joists insulation and boarding.
Loft floors loft floor construction.
Fortunately this is a fairly easy fix.
Lining walls and ceilings with a double layer of acoustic plasterboard can also be very effective as can laying a carpet over thick rubber underlay.
Ceiling joists consist of two narrow low grade timbers often bolted together sistered above a supporting wall.
In other words if your attic has 200 square feet over which the ceiling is at least 5.