Identify the sound problem first
Soundproofing and acoustic treatment solve different problems. Soundproofing reduces noise entering or leaving a room. Acoustic treatment reduces the reflections, echo, and reverb inside it. Listen to a short test recording before buying materials so you know which problem you are trying to solve.
Start with room treatment
The home studio guide describes adding rugs, furniture, bookshelves, acoustic panels, foam, and blankets to reduce reflections. These additions can improve a bare room, but they do not make it soundproof.
Control the recording setup
Place the microphone close enough to capture a clear voice, reduce controllable background noise, and compare recordings before and after each change. See the microphone guide for different recording setups.
Before structural changes
Check the source of incoming noise and the building’s requirements before altering doors, walls, or ventilation. Do not block ventilation to improve a recording. When isolation needs exceed simple room treatment, get qualified advice about a suitable construction approach.