Characteristics of Notes – Learning Outcomes Discuss the relationship between scientific and musical terms: amplitude and loudness, frequency and pitch, quality/timbre and overtones, Define the frequency limits of audibility. Discuss dog whistles

Loudness The amplitude of a sound wave is strictly the maximum distance molecules move from the undisturbed position. Waves with larger amplitudes will sound louder, so loudness depends on amplitude. Human ears do not hear different frequencies exactly the same – loudness depends on frequency also. More on frequency relationship later.

Pitch The pitch of a sound wave is almost synonymous with its frequency. Frequency is an objective measure of the rate of oscillation of the wave. Pitch is a subjective measure of the listener and may vary between people and with loudness. Even so, pitch will always change with frequency.

Quality / Timbre Most instruments do not produce a single note: they produce multiple additional frequencies called overtones. Overtones are usually integer multiples of the lowest frequency produced (e.g. 2f, 3f, 6f, etc.), but a few instruments produce non-integer ratios, particularly certain percussion and brass instruments. The quality of a musical note depends on the relative strengths of the overtones they produce. Hence different instruments and different vocalists can sound different when playing the same note: they have a different quality.

Frequency Limits of Audibility All vibrating objects produce sound, though humans can only hear frequencies within a certain range. The frequency limits of audibility are the highest (20 000 Hz) and lowest (20 Hz) frequencies that can be heard by a normal human ear. Sounds beyond the upper limit are called ultrasonic and sounds below the lower limit are called infrasonic. The upper limit typically decreases with age. Try it! Other animals have different frequency limits. Dogs can hear up to 35 000 Hz, so dog whistles tend to operate in the 20 000 – 35 000 Hz range.