Audio Engineering

Audio Principles 15

The generally accepted frequency range for high-quality audio is 20 to 20,000 Hz,
although an upper limit of 15,000 Hz is often applied for broadcasting.

The most dramatic effect of the curves of Figure 1.9 is that the bass content of reproduced
sound is reduced disproportionately as the level is turned down. This would suggest that
if a suffi ciently powerful yet high-quality reproduction system is available, the correct
tonal balance when playing a good recording can be obtained simply by setting the
volume control to the correct level. This is indeed the case. A further consideration is that
many musical instruments, as well as the human voice, change timbre with the level and
there is only one level that sounds correct for the timbre.

Audio systems with a more modest specifi cation would have to resort to the use of tone
controls to achieve a better tonal balance at lower SPL. A loudness control is one where
the tone controls are automatically invoked as the volume is reduced. Although well meant,
loudness controls seldom compensate accurately because they must know the original level
at which the material was meant to be reproduced as well as the actual level in use.

 20

2020 50 50 100100 200 200 500 500 1 1 kk 55 kk 2020 kk

Figure 1.9 : Contours of equal loudness showing that the frequency response of the ear is

highly level dependent (solid line, age 20; dashed line, age 60).