A hemiola is a rhythmic device that gives the impression of the music speeding up. Music which was originally in triple time moves into duple time. This gives the effect of triple metre moving to duple metre. The chord changes move from once every three beats to once every two beats.
Hemiolas are often found near the ends of cadences. A good example of this is bars 9-10 in Handel’s “And the Glory of the Lord” from Messiah. You can hear a hemiola at 0:03-0:04 seconds in this extract:
Diminution and augmentation are rhythmic devices that are often used in 20th century music, especially in minimalist and serialist music.
Diminution is when a musical idea is repeated with the note values halved - so the notes are shorter. Augmentation is when a musical idea is repeated but with the note values doubled, which doubles the length of the idea.
Offbeats are the weaker beats of the bar. In 4/4 time, these are beats 2 and 4. The combination of on and offbeats can often form an ‘um-cha’ accompaniment, which is used in a variety of periods and styles. Offbeats are often used in reggae music:
An upbeat is when a musical phrase starts just before the bar line. This is also known as an anacrusis. You can hear this in the opening of Mozart’s Symphony No. 40.
Rubato is when the performer is given the freedom to relax the tempo and hold it back. This can be heard in Chopin’s Raindrop Prelude, towards the end of this extract:
What is an anacrusis?