Aesthetic issues aside, you can. But it can cope with the outside noise only to an extent. Mainly, it depends on which stuff your blanket is made from. For example, wool does a decent job at dampening the sound. Actually, wool carpets have been a popular choice to muffle the noises in many mastering studios over the decades. Although opinions on their usefulness vary. But a blanket should be a blanket: originally, it wasnu2019t designed to trap the sound and mitigate reverberation. But if thereu2019s no other option for you so far, or you are waiting for your new soundproof curtains to be delivered, you should definitely try this, as music doesnu2019t wait!