Noise floor
The noise , or even English noise floor , refers to the internal noise of a single device such as an amplifier stage or a measuring device, which is only in operational condition, but performs no useful signal. In the case of measuring instruments, the level of the background noise means that signals with lower levels can no longer be recorded. The noise floor represents a lower limit of the resolution, in this case the signal-to-noise ratio (SNR) is equal to 1.
Utterance
The background noise is similar to the white noise and is perceived accordingly. The noise floor is caused by several factors. One factor that has a strong influence on the strength of this background noise is the type of device, whether it is an active or a passive device. In the case of passive components, the noise is caused by Brownian molecular motion , the heat noise . With active devices, the cause can be seen in the power supply. The more power a device has to provide, the greater the background noise can be.
Another factor is the temperature in and around the device. The higher the temperature, the greater the intrinsic movement of the particles (electrons, protons, neutrons). Furthermore, the mechanical and electrical shielding has a major influence on the behavior of the background noise. Another influencing point is the type of construction of the device. Are many components installed inside or only the most necessary. The more resistors and capacitors are built in, the greater the background noise will be. If the total resistance of a circuit is halved, the background noise is reduced by around 3 dB. However, this must be taken into account when designing the device, as subsequent changes are difficult and costly. Furthermore, the intensity of the background noise depends on the device network. At the end of almost every transmission chain there is a playback device in the form of a loudspeaker or headphones that is controlled by an amplifier. The greater the gain, the more clearly the background noise becomes perceptible.
Possibilities for reduction
In order to keep the background noise as low as possible and to reduce the audibility via a playback system, there are again several options. On the one hand, it is advisable not to expose the equipment to excessive heat, especially in summer, or to influence the cooling of the active components. Another possibility would be the use of expanders or gates that reduce or block out the background noise by artificially changing the operating point of the device. Another possibility is to cover the background noise using the useful signal.
The background noise can be perceived at any time, e.g. B. when the stereo is turned on without playing a CD or cassette. It doesn't always seem annoying or intrusive.
meaning
The noise floor represents the lower end of the technical transmission range of the device. This means that the system dynamics begin when the noise floor level is exceeded (the useful signal becomes louder than the background noise). The term signal-to-noise ratio can also be used for the system dynamics.
literature
- Thomas Görne: Sound engineering. Fachbuchverlag Leipzig in Carl Hanser Verlag, Munich et al. 2006, ISBN 3-446-40198-9 .
- Gerhard Haas : audio circuits for sound engineering, studio and PA. New, revised edition. Elektor-Verlag, Aachen 2006, ISBN 3-89576-175-3 .
- Andreas Friesecke: The audio encyclopedia. A reference book for sound engineers. Saur, Munich 2007, ISBN 978-3-598-11774-9 .