13
TUBE ULTRAGAIN T1953
0
20
40
60
80
100
120
140
160
Threshold Of Audibility
Falling Leaves
Recording Studio
Quiet Apartment
Normal Conversation
"Loud" Office
Power Drill
Threshold Of Pain
Jet Engine
Machinery Hall
Sound-Pressure Level (dB SPL)
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 (= 2*10
-5
Pa) for the threshold of audibility, any dB values can be calculated by means
of the following formula:
/
S
S
=
⋅
20
2
1
log
L = e.g. the absolute sound pressure level in dB SPL
p
1
= e.g. a reference sound pressure of 0.00002 Pa
p
2
= 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
4. TECHNICAL BACKGROUND
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