TUBE ULTRAGAIN T1953
| 160 | |
SPL)(dB | 140 | |
120 | ||
| ||
Level | 100 | |
80 | ||
Pressure- | ||
60 | ||
Sound | 40 |
20
0
Jet Engine
Threshold Of Pain
Power Drill
Machinery Hall
"Loud" Office
Normal Conversation
Quiet Apartment
Recording Studio
Falling Leaves
Threshold Of Audibility
Fig. 4.1: Dynamic range of human hearing
The range of sound pressure levels or the dynamic range of human hearing encompasses a factor of 10,000,000. This enormous range of values is difficult to handle and additionally does not represent the subjective perception of sound, since human hearing tends to use a logarithmic curve. When an increase in loudness by the factor two is perceived as one step, four times the loudness level equals two steps. So, the decibel is a unit of measurement that describes a level in relation to a reference quantity. To make clear which reference quantity is meant, the abbreviation SPL (sound pressure level) is sometimes used together with dB. Starting with a value of 0 dB SPL (=
/= 20 ⋅ logS 2
S 1
L = e.g. the absolute sound pressure level in dB SPL p1 = e.g. a reference sound pressure of 0.00002 Pa
p2 = the sound pressure (in Pa) produced by the sound source to be calculated log = decimal logarithm.
As can be seen, human hearing has a very wide dynamic range of about 130 dB, which surpasses the range of a DAT or CD player with an approximate range of 96 dB. From a physical point of view, a 3 dB boost corresponds to an increase in power by the factor 2. However, the human ear perceives a signal to be twice as loud as before only if it is boosted by about 10 dB.
4.1 Audio dynamics
As demonstrated, it is possible to manufacture analog audio equipment with a dynamic range of up to 130 dB. In contrast to analog techniques, the dynamic range of digital equipment is approximately 25 dB less. With conventional record and tape recorder technology, as well as broadcasting, this value is further reduced. Generally, dynamic restrictions are due to noisy storage in transmission media and also the maximum headroom of these systems.
4.1.1 Noise as a physical phenomenon
All electrical components produce a certain level of inherent noise. Current flowing through a conductor leads to uncontrolled random electron movements. For statistical reasons, this produces frequencies within the whole audio spectrum. If these currents are highly amplified, the result will be perceived as noise. Since all frequencies are equally affected, we term this white noise. It is fairly obvious that electronics cannot function
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