A unit of measurement of the loudness or strength of a signal. One deciBel is considered the smallest difference in sound level that the human ear can discern. Created in the early days of telephony as a way to measure cable and equipment performance and named after Alexander Graham Bell, deciBels (dBs) are a relative measurement derived from two signal levels: a reference input level and an observed output level. A deciBel is the logarithm of the ratio of the two levels. One Bel is when the output signal is 10x that of the input, and one deciBel is 1/10th of a Bel.
A whisper is about 20 dB. A normal conversation is typically from 60 to 70 dB, and a noisy factory from 90 to 100 dB. Loud thunder is approximately 110 dB, and 120 dB borders on the threshold of pain. See dBm.
Bels and Bells
Quite a lot was named after Alexander Graham Bell. Throughout the 20th century, the Bell name was ubiquitous. It will live on with the deciBel.
A whisper is about 20 dB. A normal conversation is typically from 60 to 70 dB, and a noisy factory from 90 to 100 dB. Loud thunder is approximately 110 dB, and 120 dB borders on the threshold of pain. See dBm.
INCREASE IN POWER LEVELS (WATTS)
Formula is dB=10*log(P1/P2)
DeciBels Output Signal Strength
3dB 2x
6dB 4x
10dB (1 Bel) 10x
20dB 100x
30dB 1,000x
40db 10,000x
ATTENUATION OF AMPLITUDE (VOLTS or AMPS)
Formula is dB=20*log(A1/A2)
DeciBels Output Signal Strength
-3dB 0.707x
-6dB 0.5x
-10dB 0.316x
-20dB 0.1x
-30dB 0.032x
-40db 0.010x
Bels and Bells
Quite a lot was named after Alexander Graham Bell. Throughout the 20th century, the Bell name was ubiquitous. It will live on with the deciBel.
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2009 The Computer Language Company Inc. All rights reserved. |
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