How are decibels used in electronics

Decibel (dB)

Decibel is not a unit like volts, amperes or watts, but a ratio. For numbers with the unit dB, two other numbers were set in relation to one another beforehand. It is basically a mathematical statement that alone is not meaningful. That is why the dB specification must also include what it specifies. The physicist Alexander Graham Bell was honored with the designation Bel.

The decibel (dB) is the tenth part of a bel (B). Just as a decimeter is a tenth of a meter.

  • 1 bel is 10 decibels.
  • 1 meter is 10 decimeters.

Why is it stated in decibels (dB)?

As a signal propagates in space, the power is reduced proportionally to the square of the distance. For this reason, HF technology is based on power and not on voltages. The services are converted into decibels (dB). Calculations can be simplified significantly by simply adding or subtracting gains or losses. Otherwise one would have to multiply in several calculations. In addition, dB values ​​are much more manageable.


In the example above, the amplifier has a gain factor V of 50. The output signal is 50 times greater than the input signal. In order to get the gain factor to decibels, the logarithm of ten is formed from the gain.

One advantage of converting with the help of the logarithm is the ease with which the ratios of two similar quantities can be handled. Such relationships occur with amplifiers and transmission links. Unmanageable values ​​then arise on a linear scale. The logarithm offers smaller values ​​and makes it easier to calculate gains and losses. A multiplication becomes an addition and a division becomes a subtraction.

Calculation example


If several amplifier stages and transmission links are used one behind the other, the gain factor has to be multiplied each time. If the gain is given in dB, then these values ​​can simply be added.
It is preferable to calculate with decibels in order to be able to calculate the amplification or attenuation of electrical signals by simply adding and subtracting them. The smaller numbers are also advantageous. In contrast, the gain factors and attenuation factors, the values ​​of which are calculated by multiplication and division. The numerical values ​​are high and cannot be calculated in your head.

Calculation with gain factor:

Calculation with gain in dB:

Noise scale

In addition to the electrical gain, volume levels are also given in decibels. The level of the volume is given in relation to the volume at the hearing limit.

Source: Federal Environment Ministry

dBdescription
0Hearing threshold
10Rustling leaves, calm breathing
20low whisper
25Commercial noise limit at night
35Upper limit for night noises in residential areas, sleeping, learning and concentration disorders possible
40quiet conversation
45Upper limit for daytime noise in residential areas
50normal conversation, room volume
60loud conversation, stress limit
65increased risk of cardiovascular diseases up to and including myocardial infarction
70Household and office noise
85Hearing protection prescribed in the trade, if exposed for years, hearing damage occurs
90Car horns, truck driving noises, snoring
100Motorbike, circular saw, disco music
110Walkman loud, rock concert
120Airplane at a short distance, techno music, hearing damage possible after only a short exposure
130Pain threshold, jet plane at a short distance
140Gun shot, rocket launch, EU limit value to protect against hearing damage
170G3 rifle at close range, slap directly in the ear
190internal injuries, skin burns, fatal

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