Although piano tremolos and trills sound much the same, there are differences between how they are notated and how they sound. A trill occurs when you flutter your fingers very quickly between two notes that are close together, either a half step or whole step apart. So, what do you call fluttering between two notes that are farther apart? Well, you call it whatever you want, but the world of music calls it a tremolo.
To play a tremolo, pick an interval, any interval larger than a whole step, and alternate playing the two notes as quickly as possible. Like a trill, this sounds as if you're playing a bunch of 32nd or 64th notes. But unlike the notation for a trill, which just puts the letters "tr" above one note, the notation for a tremolo actually shows you both notes that your fingers rumble between (see Figure 1).
In Figure 1, you see that the two notes of a tremolo are shown with the same note length. At first glance, this notation looks like too many beats are in each measure, but the three diagonal lines between the notes signal you that this is a tremolo. These two notes share the note length. Therefore, you only count the beats of the first note.
Tremolos of any size sound great played by either hand. Probably the most popular left-hand tremolo is the octave tremolo. Stretch your hand over a C octave and let this interval rumble in a familiar melody. After one listen, you may know this as the theme to the movie 2001: A Space Odyssey.
You can also play tremolo chords. All you do is break the chord into two parts: a bottom note and the remaining top notes. Tremolo these notes by alternating between the top and bottom notes as quickly as possible. Tremolo chords may look intimidating, but if you can play the chord, you can play the tremolo.
Figure 2 gives you a chance to play a few tremolo chords. For the first measure of Figure 2, put your hand in position for a G major chord and rock between the top notes (B and D) and the bottom note (G) very quickly. Move to the next measure and do the same with a 2nd inversion C chord, and so on, and so on.
Tremolo chords come in handy when playing rock 'n' roll, especially as part of a band. A tremolo turns the otherwise dull task of playing straight chords into a sizzling rhythmic romp.