Piano pedals (2) - soft pedals - una corda, half-blow and celeste

Having dealt with the sustain pedal in my last article on the topic, I wanted to turn to the function of the left pedal (and in some cases the middle pedal if you have one). This time I intend to cover the the pedals on a piano that are intended to make the sound softer, which are of three main types: (true) una corda, half-blow and celeste. I should point out that in music the indication for the left pedal is "una corda" so sometimes this term is used to cover all the types, but in fact the mechanism generally works in a quite different way on an upright as compared with a grand. There are two other common pedal functions (sostenuto and bass damper lift) which do not fall into the category of soft pedals and will be covered in a third article.

So, at this point we need to cover the slightly complex question of what the pedal functions are, depending on whether you have a grand or upright, and whether it has two or three pedals. In the last article, I explained that uprights can have an underdamper action (dampers below the hammers) or an overdamper action (dampers above the hammers). For the purpose of this article, it may be useful to know whether your piano has an overdamper or underdamper action, and whether it is overstrung (bass strings cross over the treble ones) or straight strung (strings run straight up and down the piano). All modern pianos (more or less anything built after 1945) will be of the overstrung underdamper type.

If you don't want to spend time looking inside your piano, don't worry too much as it's usually possible to tell what your pedals do just by listening to them.

If you have a grand piano:

• If it has two pedals, the left pedal will normally be a (true) una corda, whilst the right pedal is (as always) the sustain pedal.
• If it has three pedals, the left will normally be the una corda, the middle will normally be the sostenuto, and the right will be the sustain pedal.

If you have an upright piano: 

• If the piano has two pedals and an underdamper action, whether overstrung or straight strung, the left pedal will normally be the half blow pedal,  and the right pedal will be the sustain pedal.
• If the piano has two pedals and is overstrung with an overdamper action, the pedal functions are frequently the same as for an underdamper action, but sometimes (but not always) the left pedal is a celeste pedal instead of a half-blow.
• If the piano has two pedals and is straight strung with an overdamper action (in the UK this is a significant minority of older instruments), the left pedal is in the great majority of cases a celeste pedal, may occasionally be a half-blow, and in a very few cases may be a true una corda, of which more later. The right pedal, as always, is still the sustain pedal.
• If the piano has three pedals it normally has an underdamper action (I've never seen three pedals on an overdamper, thought possibly a few may exist). In this case, the left pedal is normally a half-blow pedal, and the middle pedal is most commonly a celeste pedal, though more rarely, it is a sostenuto pedal, or a bass damper lift pedal.

Also, on a few (mainly older) pianos with three pedals, the middle one is just a dummy pedal that does nothing at all - generally these are American instruments since, as I had already mentioned, most older European-made pianos don't have a third pedal at all.

The Una Corda pedal

So now to demystify what these terms mean. The una corda pedal was actually the very first device used to change a piano's tone - its history goes all the way back to Bartolomeo Cristofori, the inventor of the piano. Cristofori began building pianos around 1700, and an una corda stop is featured on a surviving piano which he built later on (1726).

To understand how, and why, the una corda works, I have again used this action diagram for a grand piano:

What I've shown here is that the grand action consists of two parts - the main action, which controls the hammer striking the string, and the damper mechanism (to the left of the red line), which comprises the damper rail, damper underlevers and the dampers themselves. The function of the una corda is to move the hammers across slightly, thus striking two of the three strings (on trichords) and one of the two on bichords. This is done by a system of levers (trapwork) underneath the piano that cause the main action to be pushed slightly to the right - the action is returned to its original position by a strong spring when the pedal is released. As the entire action is shifted, the keyboard can be seen moving physically to the right.

The key thing about the operation of an una corda pedal is that the hammers should move in relation to the strings, whilst the dampers should not - these need to damp all three strings exactly as they normally would. This is quite easy to achieve on the grand action as the dampers are separate from the main action, but (as will be seen) very difficult on an upright.

The term "una corda" (Italian: "one string") comes from the fact that early pianos normally only had two strings per note, so the pedal was intended to have the hammers strike one of these. On a modern piano, normally two strings are struck, so "due corde" would be a more accurate term, but the earlier nomenclature has stuck.

This is almost invariably the function of the left pedal on a grand - if your grand piano has a middle pedal it will normally be a sostenuto pedal, which will be covered in the next article.

Half-blow pedal

This pedal is normally only found on an upright piano - it's essentially the "substitute" for a true una corda pedal. Its function is shown in the picture below:

The left pedal operates a rocker which pushes up the pedal stick (the red arrow is pointing to the top of this), the effect of which is to move a hinged part of the hammer rail closer to the strings. As the line of hammers is now closer to the strings, the volume when playing will be reduced.

Though both the half-blow and una corda pedals have the effect of reducing the volume, the una corda also changes the tone (due to striking two strings instead of three); the half-blow simply reduces the volume. Additionally, some pianists may notice a change in the feel of the keys when the half-blow pedal is in use - this is due to the fact that something technically known as "lost motion" is introduced - I won't try to explain this in full here, but it means that the keys will go down a little way before starting to propel the hammer, rather than doing so immediately.

Celeste pedal

The celeste rail on a Yamaha U1, which lowers a piece of felt in front of the strings.

This pedal is also normally found only on upright pianos - its other names included the "muffler pedal" and "practice pedal". Quite simply, it inserts a piece of soft felt material between the hammers and the strings. This arrangement is commonly found as the middle pedal on more modern (and a few older) uprights which have three pedals and an underdamper action, or as the left on older straight-strung overdamper uprights. Please note that overstrung overdamper uprights normally have a half-blow which moves the hammers closer to the strings, just the same as an underdamper.

When found on an underdamper, the celeste rail normally has spring-loaded support brackets that makes it stand above the action, and the pedal lowers the celeste into place. On the older straight-strung overdampers, because the dampers are above the line of strings, the celeste rail sits at the back of the action and is pushed up from below. In either case, the rail normally needs to be removed when tuning - in the case of the underdampers because it is sitting in front of the tuning pins and for the overdampers because it impedes wedging.

A device similar to a celeste (often called a moderator) was a feature of several early pianos - e.g. the Viennese maker Graf included two different thicknesses on his pianos in the 1780s. These were originally made of leather or cloth, sometimes cut into strips to allow the strings to vibrate more freely.

Is it possible to have a true una corda pedal on an upright?

The Wikipedia article on piano pedals quotes a work by Edwin Good, entitled: Giraffes, Black Dragons, and Other Pianos: A Technological History From Cristofori to the Modern Concert Grand, as saying that an una corda pedal on an upright is impossible because the strings "run at such an oblique angle to the hammers that if the action were moved sideways, the hammer might strike one string of the wrong note".

In fact, I do not believe this is the main reason why upright pianos scarcely ever have an una corda pedal. After all, some small baby grand pianos have strings that run at an oblique angle (a few are even double overstrung), yet still have an una corda, whilst even larger or stright-strung uprights hardly ever have one. In my view, there's no reason that problem couldn't be overcome by careful string-spacing and action placement. The real cause of difficulty can be seen by looking at a diagram of an upright piano action:

Upright action diagram - this is typical of an older American upright

The key point here is that the hammer butt (yellow, top right) which carries the hammer, the lever (yellow, lower down), which carries the jack, and the damper body (blue), which carries the damper, To achieve an una corda, the levers and hammers need to move across (the two yellow pieces), but the blue damper bodies need to stay where they are. To achieve this you would somehow have to split the wooden beam so that the part that carries the dampers (and the damper lift rod, which is hinged to the beam) stays in the same place, but the rest of the beam moves across. This would be extremely difficult and fiddly in practice.

So is it impossible to have a true una corda on an upright? The answer is no, though they are extremely rare; whilst it is near-impossible to achieve on an underdamper action, it is perfectly possible on an overdamper, because the dampers are attached to a separate rail above the main action. This is still uncommon in practice, but I have come across a couple of these on my rounds and here is a video of a German piano tuner playing another: