Frequency Spectrum of Sounds
With the exception of pure sine waves, sounds are made up of many different
frequency components vibrating at the same time. The particular characteristics of a
sound are the result of the unique combination of frequencies it contains.
Sounds contain energy in different frequency ranges, or bands. If a sound has a lot of
low-frequency energy, it has a lot of bass. The 250–4000 Hz frequency band, where
humans hear best, is described as midrange. High-frequency energy beyond the
midrange is called treble, and this adds crispness or brilliance to a sound. The graph
below shows how the sounds of different musical instruments fall within particular
Note: Different manufacturers and mixing engineers define the ranges of these
frequency bands differently, so the numbers described above are approximate.
Tip: The human voice produces sounds that are mostly in the 250–4000 Hz range,
which likely explains why people’s ears are also the most sensitive to this range. If the
dialogue in your movie is harder to hear when you add music and sound effects, try
reducing the midrange frequencies of the nondialogue tracks using an equalizer filter.
Reducing the midrange creates a “sonic space” in which the dialogue can be heard
Violin and flute
Musical sounds typically have a regular frequency, which the human ear hears as the
sound’s pitch. Pitch is expressed using musical notes, such as C, E flat, and F sharp. The
pitch is usually only the lowest, strongest part of the sound wave, called the fundamental
frequency. Every musical sound also has higher, softer parts called overtones or harmonics,
which occur at regular multiples of the fundamental frequency. The human ear doesn’t
hear the harmonics as distinct pitches, but rather as the tone color (also called the timbre)
of the sound, which allows the ear to distinguish one instrument or voice from another,
even when both are playing the same pitch.
Musical sounds also typically have a volume envelope. Every note played on a musical
instrument has a distinct curve of rising and falling volume over time. Sounds
produced by some instruments, particularly drums and other percussion instruments,
start at a high volume level but quickly decrease to a much lower level and die away to
silence. Sounds produced by other instruments, for example, a violin or a trumpet, can
be sustained at the same volume level and can be raised or lowered in volume while
being sustained. This volume curve is called the sound’s envelope and acts like a
signature to help the ear recognize what instrument is producing the sound.