Sometimes you play a piano and it sounds and feels odd. It’s not the tuning, (though that may be a separate issue) but it just doesn’t feel right. It may in fact be that the piano hammer is striking the string twice in quick succession. Piano technicians usually refer to this effect as bubbling. Often times the cause of the note bubbling is insufficient key travel. When the key is depressed by your finger, it doesn’t travel far enough before it hits the keybed. Many times this happens in the middle of the piano. As pianos settle with age, the middle of the keyboard can sag making the appearance of a smiley face. The keys in the middle are lower than the keys in the bass and treble extremes. A piano technician will shore up these middle keys, making a straight line from the top to the bottom of the keyboard. In the instance of this picture, a Zimmerman piano from Europe needed the middle keys to be raised, allowing for greater key travel. I brought these keys up with paper punchings, which are placed under the balance rail felt. Now that the key travel is corrected, the hammers no longer bubble or double hit and the piano has been restored to the manufactures’ specifications.