Audio Engineering

Measurement 77

For a harmonic to be equal to  33 dB, its percentage would be

100 10 2 24

2033

    



.%.

For a harmonic to be equal to  49 dB, its percentage would be

100 10 0 355

2049

    



.%.

2.27 Decibels and Percentages ........................................................................................

The comparison of data in decibels often needs to be expressed as percentages. The
measurement ofTHD compares the harmonics with the fundamental. After fi nding

90

80

70

60

50

40

30

LP

16 31.5 63 125 250 500 1k 2k 4k 8k 16k

Frequency (Hz)

Peak

rms

Figure 2.21 : Male speech, normal level 2 ft from the microphone.

LP

16 31.5 63 125 250 500 1k 2k 4k 8k 16k

Frequency (Hz)

Air conditioning "on"

Instrument threshold

Air conditioning "off"

50

40

30

20

10

0

 10

Figure 2.22 : Ambient noise levels.