They're often overlooked.
Let's be honest. When we're watching a pianist play, it's the hands we're most interested in looking at.
Much like driving a car, though, there's some activity in the feet that isn't so obvious before you try it yourself - remember the clutch on your first driving lesson?
So lets look at what the pedals actually do.
Sustain - notated as Ped to come on and * to come off
This is the most often used of the three. On an acoustic piano, this physically lifts the dampers off the strings, allowing them to resonate freely once the keys are pressed, literally 'sustaining' the sound. Once the pedal is released, the dampers fall back onto the strings and silence them.
Piano dampers at rest on the strings, silencing them.
Sostenuto - Notated as S.P, Sost. or ThP
This is one of the less well known and indeed used pedals. On a grand piano, this functions like the Sustain Pedal, with a slight twist - it only sustains the notes being played at the moment the pedal is depressed. This allows the player to hold a bass note while playing staccato melodies over the top of the music, for example.
On Upright Pianos, this is sometimes a 'practice' pedal which lowers a layer of felt between the hammers and the strings, muffling the sound.
Una Corda - Notated as Una Corda with Tre Corda to release
The leftmost pedal has changed a little over time. Originally in acoustic pianos, the sound of many of the treble notes is obtained from 3 strings tuned to the same note - This is why they sound so awful when they're out of tune! - and the Una Corda pedal physically shifts the action across, so that the hammer only struck one string instead of 3. This therefore affects the volume and tone. In modern construction, due mainly to space constraints, the Una Corda still shifts the action but now the hammer hits 2 strings, rather than 1, so there is a difference in volume and tone again compared to older pianos. On upright pianos the function is usually different again - it tends to move the hammers closer to the strings, so that only volume is affected but not the tone, as all 3 strings are still being played on each note.
Digital Pianos
The mechanics are all well and good in an acoustic, but what about a digital piano?
All digital pianos support at the very least a sustain pedal, but they don't all have the option to extend this to the 3 pedals above. Everything they replicate, as suggested, is a digital impression of how it works.
Different specification pianos offer different levels of realism with the pedals. Latest pianos offer 'half pedalling' which is more realistic than the older style of 'on/off' swich pedals, which are quite unrealistic when compared to a real piano. Many newer models, like Casio's latest Privia and Celviano range, offer 'string resonance' as added software. This replicates the resonance of the strings when played with the sustain pedal and is quite effective.
I want a digital piano - how many pedals am I going to need
This is a popular question, and it's really down to your own usage. If it's just for basic practice and not replacing a main piano, or maybe just for some experimentation and getting used to the piano sounds and touch, a sustain pedal will be more than adequate - so no more than 1 pedal.
For serious practising or as a replacement for an old acoustic piano, you'll need a piano with all 3 to avoid limiting yourself. It's worth bearing in mind also that for graded piano exams, all 3 pedals will appear in the music at all grades above 5 - not having them will make it difficult to replicate the music properly, and can be confusing in the exam as you do use a real piano!
If you need any further advice or would like to talk through our range of acoustic and digital pianos, do contact a member of our Sales Team.