Audio Engineering Society

Chicago Section

Meeting Review, December 9, 2008


other meeting reports

12/9/08 Meeting Highlights
by Ryan Scott

Piano Tone, Tuning and Inharmonicity

By: Dave Carpenter

 

Dave Carpenter presented “Piano Tone, Tuning and Inharmonicity” to approximately 20 members of the Chicago AES chapter. Dave is an adjunct faculty member at the Chicago School for Piano Technology, the founder of Veritune, Inc. and a Ph.D. Candidate in Acoustics at the Pennsylvania State University. The presentation began with Dave outlining the basics of the piano including the action mechanisms, soundboard, vertical vs grand pianos, and the fact that with 220 strings the frame and soundboard must support almost 220 tons of tension. Dave transitioned to the world of audio and physics by playing some sound clips of the piano with and without the string harmonics present, highlighting their importance to the tone. He then discussed the difference between an ideal string and the stiff string that is actually found on a piano. The piano string has an extra restoring force due to its stiffness that causes harmonics to be non-integer multiples of the fundamental. The upper harmonics of a piano string become proportionally sharper and sharper, hence the inharmonicity of the piano. Dave then talked about how this leads to the “Pythagorean Comma”, the 23.5 cents left over on the piano, and how octave stretching acts to distribute this across the keyboard.

 

After explaining piano basics, Dave moved on to explain the art and science of piano tuning. Sometimes called beat counters, the piano tuner plays two notes and listens to the beat frequency caused by the interaction of upper harmonics. To obtain the correct octave stretching, certain intervals are in tune when upper harmonics beat at a specific number of beats per second. Audio clips were used to demonstrate just how difficult this can be. Dave then discussed the Veritune system and its evolution from early electric tuners. The Veritune system takes measurements across the keyboard and calculates the optimum distribution for the octave stretching using new processing which accounts for perceived dissonance. A demonstration of the Veritune system was followed by a Q&A session with Dave covering some interesting points such as seasonal humidity effects on pianos and the fact that there used to be 120 piano manufacturers in Chicago! The Chicago AES chapter would like to thank Dave for a very interesting talk.