Music and Instruments

Introduction

Musical notes on a keyboard or a trumpet have a pitch, a volume, and a duration. These notes are just sound waves, or combinations of sound waves. The pitch corresponds to the frequency, while the volume corresponds to the amplitude.

Making music

Click on the figure below to interact with the model.

Figure 1. A circuit for a simple electronic organ.

The circuit in Fig.1 could be used inside a simple electronic organ. Push the buttons to produce different notes.

Musical notes

The circuit in Fig.2 below has a graph at the bottom of the page that represents the notes graphically. This is just like the graph you would see on a cathode ray oscilloscope (CRO). The horizontal axis is time and the units are milliseconds (ms).

Click on the figure below to interact with the model.

Figure 2. A circuit for a simple electronic organ, with graph.

Press and hold down C. You will not hear a sound this time, but use the graph to measure the period of C (this is the time it takes for the wave to repeat itself). The simulation will automatically pause when the graph is full to give you have time to make the measurement from the graph. Simply push a button to start the sound again.

Use the equation below to convert the period of middle C into its

frequency

In general, the frequency of an event describes how often it occurs. When talking about waves, the frequency is a measure of how many waves go past a fixed point in a given time.frequency. (Remember, 1 ms is equal to 0.001 s)

Now try pressing the other notes. Compare how high or low the notes sound. This is called their pitch.

Look at the waves on the CRO made by the different notes. The waves made by middle C are the most spread out. The frequency of middle C is the lowest of these seven notes.

Large instruments make lower sounds than smaller instruments. For example, a double bass is much larger than a high-pitched violin, and plays lower notes. The long strings on a piano or a harp produce deeper notes than the short strings.

Human ears are sensitive to sounds with frequencies between around 20 Hz and 20,000 Hz. This range is known as the audible range. Some animals have hearing which is sensitive to sounds outside this frequency range.

Summary

The pitch of a musical note is related to the frequency of the sound wave.

A high-pitched note has a high frequency, while a low-pitched note has a low frequency.

Large instruments produce deeper sounds than small instruments.

Humans can hear sounds in the frequency range 20 Hz to 20,000 Hz.

Exercises

3. A microphone is used to record three different sounds. The displays on the CRO are shown below. Decide which note has a high pitch, which has an intermediate pitch and which has a low pitch.

Click on the figure below to interact with the model.

Figure 3.

Well done!

Try again!