2-5 Beats
What happens when two waves of different frequencies go through superposition?
We have already learned that two waves of different frequencies will not become a standing wave when going through interference. Therefore, what will occur?
Imagine, a Bb clarinet and an Eb clarinet both playing an C. What sound will we hear?
Imagine, playing a B and a C on the piano. What sound will we hear?
Musically, we say that these sounds are dissonant because they produce a sound which is unpleasant to the ear. The clash of pitches display tension and a harsh tone. Listen to a dissonant sound here: Dissonant Piano Chords
When two waves of difference frequencies are superimposed (such as during dissonant chords), beats are produced.
What happens to the resultant wave when beats occur?
When the beats are produced, the resultant wave will be the average of the two individual waves.
This is shown here:
As you can see, the amplitude of the resultant wave varies. There is no simultaneous pattern. This fluctuating amplitude is said to be the "beats".
What does beats have to do with tuning your instrument?
Now that you know about beats, how do you think they play a part in tuning your instrument?
Do you think beats will occur between two instruments if they are in tune?
No, if instruments are in tune the frequencies of the sound waves will be the same and therefore no beats would be produced. However, if the two instruments are out of tune the frequencies would be different and you would hear beats. This is why you hear tension and a clashing sound if someone in your duet is playing out of tune.
Practice Problems:
1. In which case would you hear beats?
(a) A trumpeter playing an a capella solo 10 cents off from perfect pitch.
(b) Two clarinets playing in unison with both players tuned to 435 cents.
(c) A violinist playing a duet with the piano with her G string 5 cents sharp.
Continue: #REDIRECT 2-6 Complex Tones
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