This is the frequency plot of the 1000 Hz pure tone we listened to in the previous section.

• Frequencies, expressed in Hz, are represented along the the x axis.
• The intensity of the tone is represented, as a function of f, along the y axis. The intensity is expressed in dB (decibels). We will not enter in deep details about this unit, but might be worth saying a couple of things.

ABOUT THE DECIBEL SCALE

1. As you can see, the intensities are negative: this is simply because they are probably measured with respect to the maximum intensity allowed by the device. Thus, intensity = 0 dB corresponds to the full scale and is the highest intensity value.
2. What is important in a decibel scale is the difference between two intensities. A 20dB difference implies that one intensity is reduced of a factor 100 with respect to the bigger one. So the rule to find the reduction factor is this: divide the difference in dB by 10 and then rise 10 to what you get.

Example:

Intensity 1 is I1 = -20 dB

Intensity 2 is I2 = -25 dB

The Difference is 5 dB,

Divide the Difference by 10: 5/10=0.5

Reduction Factor: 10^0.5 ~ 3.16

The Frequency DISTRIBUTION of a pure tone

Now we have some knowledge of the Intensity units. It is time to carry out reflections about the frequency plot of our "pure tone". The following form will guide you through.

To use the Form in your class and collect privately your results, make a copy of the Google Form on your computer, then submit it, as an owner, to your students.