Every piano has its own unique tone. Tone is different from pitch. Pitch refers to the frequency (the sound wave generated by the vibrating string), controlled by the thickness and tension of the string, in which the tension can be adjusted through the process of tuning. The tone of a piano on the other hand, often refers to timbre (a note's character or quality), which is made up of a series of harmonic partials. A bright sounding piano, for example, has more higher-partials, whereas a mellow sounding piano has more lower-partials. Every player has their own preferences, and different tonal characters could pair well with different styles of music. Over time, the tone of a piano will change through the wearing of hammer felts and should be restored by the voicing procedure.
There are many words to describe the tone of a piano: mellow, deep, harsh, brittle, metallic, lively, rich, bright, dark, nasally, glassy, warm, full singing, thin, robust, delicate, soft, sweet, loud, to name more than a few. These descriptions are often used by pianists to describe what they hear or want to hear when they play their instruments. A well-voiced piano should have good sustain, power, clarity, and a range of tonal colors to match the wide dynamic range.
What is voicing?
Voicing is a series of various procedures resulting in changes in the tonal production often through manipulation of the resilience, hardness, or shape of the hammer felt.
Prior to voicing, the piano should be well-tuned. Occasionally a player will request a voicing service, but to find that the sound they were hoping for was simply accomplished by having the piano tuned. This also brings the piano to a good baseline for the technician to analyze.
The technician will also check hammer-to-string alignment, string condition, and other regulation issues that should be addressed before voicing. After going through these steps, the technician will determine what changes to make to the hammer felt. Through time and play, the hammer felt becomes hard, worn, and compact, often creating a tone that sounds too bright and harsh. The technician will vary their approach depending on the type of hammer and the tone they want to achieve.
Some techniques involve inserting needles into the felt with attention to the location, depth, and angle, to create elasticity that improves dynamic range and sustain. All seemingly minor decisions yield different results. The hammers may also need to be reshaped, as they become flattened and indented from the repeated heavy contact with the strings. Most hammers can be reshaped a few times in their lifetime, and become less and less effective after the first reshaping. Technicians also sometimes use hardening solutions on the felt, if needed.
The voicing process requires a lot of precision, skill, and experience, thus, approaching it in an amateur fashion could easily cause permanent tonal damage to a set of hammers.
How do you know a piano needs voicing?
If the piano just doesn't sound quite the same as when you first bought the piano, or if the piano sounds too loud or too soft, chances are, it needs a voicing session to restore the shape, tension, and hardness of the felt.
A pianist can discuss what they want with their technician. Perhaps they want to restore the piano to its factory original tone, or maybe they have something customized in mind.
Tone to fit the situation
The technician will also take into account how the piano is used before undergoing the process of voicing. For example, a piano on a stage sounds different to the pianist than it does to the audience, and this needs to be taken into account. A piano used in a recording studio may need to be voiced differently to allow for an easier mixing process. The acoustics of the room and how the piano sounds with the lid open vs closed will also need to be considered.
Voicing new pianos
It is very common for new pianos to need voicing due to the cost of doing that in the factory or showroom. In these instances, the hammers are new with fresh felt and have loads of potential to be unlocked by a qualified technician.
Regular home pianos are recommended to be voiced once every 5-8 years. Pianos that receive heavy use or have high tonal demands such as teaching studios or concert halls may need to be voiced every 1-5 years. If you are noticing any undesirable changes in the tone of your piano, discuss it with your technician.