3-5 Perception of Two Pure Tones
What affects the perception of two pure tones?
- The frequencies of the component tones
- The individual listening to the tones
How does frequency affect the perception of two pure tones?
What sound do we hear when f1 = f2?
- Unison pitch- this occurs when two clarinets (that are in tune) play the same note at the same time. They are said to be playing in unison.
What happens to the sound if f1 stays the same and f2 increases?
Hint: Again, let's think of our two clarinets. If the one clarinet stays on the same note, while the other clarinet plays a note with a higher frequency what do we expect to hear musically?
- Higher pitch- we already know that a higher frequency correlates to a higher pitch
- Loudness increases- because the amplitude (height of the wave) varies, the loudness level will also be altered.
What is the relationship between amplitude and loudness?
When amplitude is at it's maximum, loudness is also at it's maximum. However, whenever the amplitude goes through one complete cycle (wave goes from top to bottom and back to the original position), the loudness level will complete two full cycles. Therefore, the loudness will reach it's peak twice in the time it takes the amplitude to reach its maximum.
What is happening to the loudness level when we hear beats?
Review: Remember, beats occurs when two waves with similar (but different) amplitudes and frequencies are being superimposed.
When beats occur, the loudness level will be alternating. This is the "wah-wah" sound we hear when two instruments are playing out of tune. Since the frequencies and amplitudes are changing, it will cause the loudness level to change as well.
The rate that the volume is oscillating from the highest to the lowest point is known as the beat frequency. The beat frequency is equal to the difference between the component notes' frequencies.
Beat frequency = f2-f1
Practice Problems:
1. If a wave with frequency 320 Hz is superimposed with a wave of 400 Hz. What is the beat frequency?
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