Feedback

A feedback, including feedback, feedback or feedback [fi ː d ˌ Bæk ] ( English), is a mechanism in signal-enhancing or information processing systems, in which a portion of the output is fed back directly or in modified form to the input of the system.

• 3.1 Electrical circuit technology
• 3.2 sound
• 3.3 In computer technology
• 3.4 The Earth System and Climate Research
• 3.5 Medicine and biology
• 3.6 Psychology

Types of feedback

Feedback are ubiquitous in engineering, biological, geological, economic and social systems. Depending on the nature and direction of the recirculated size occurs due to self- reinforcement of the system process, or the reduction or self-limiting. In the first case we speak of positive feedback or positive feedback, in the latter case of negative feedback or negative feedback.

In technical systems are often sought to limit feedback operations not only by the capacity of the energy storage involved, but also to provide a structure that prevents passive and active feedback congestion. It often is regulation processes.

In nature, feedback can occur in complex structures in which, back acting elements over others, some remotely located systems on themselves.

In psychological determinate behavior, the direction of the feedback is not fixed from the outset. Thus, for example in the system learning in school a bad grade rating, depending on the motivation both to increased diligence ( negative feedback ) or in turn lead to the resignation ( positive feedback or reinforcing effect ).

Positive feedback

When positive feedback is a sign or phase correct feedback of the output variable in interaction with reinforcing elements of the system to bear. This can be useful, for example, to compensate for friction losses, but it can also be a danger, because the quantities involved can this dangerous grow, as long as this energy is provided, and it can, if not additional, to the process damping force acting variables are effective, be destroyed. Here, the process is limited only by the limitation of the (energy) resources.

In technical systems we speak of an undamped periodic oscillation in resonance or an aperiodic oscillation. Depending on whether it can come to an avalanche-like swelling in the system or not, we distinguish between subcritical, critical or supercritical positive feedback.

Positive feedback is often found in growth processes. One speaks in a non- technical systems, of a virtuous circle, or if the result is not desired as such, even by a vicious circle or a vicious circle.

Examples: debt trap chain reaction autocatalysis, Acoustic feedback, Stock Market Crash, electronic circuits such as Schmitt trigger or oscillators ( Meissner circuit for realizing an undamped resonant circuit ), Benjamin Franklin Effect of Social Psychology

Feedback

In the negative feedback a feedback of the output signal with a negative sign or opposite-phase polarity is effective. This negative feedback counteracts the external stimulus, resulting in a decreasing state change. Such systems tend to either strongly to occupy a stable position or to more or less decaying oscillatory behavior around a stable mean.

The negative feedback is a fundamental principle in all biota and used in technical systems. In particular, the control technique has the aim of establishing the negative feedback such that a stable system response is achieved. To this end, in technical systems automatic controller can be used.

Unwanted tendency to oscillate in a control loop can be avoided, for example, by variable dimensioning of the negative feedback by the gain is reduced with increasing frequency.

The characteristic feature in natural systems are feedback loops with self-regulation properties. In biological systems, organisms of this principle is critical in homeostasis. Coupling to play a role at all ( self) preservation processes.

Self-excitation (ie the initial emergence of oscillations) occurs initially when a positive coupling and then a delay, a negative feedback. The system parameters then commute between rest and typical maximum values ​​. This can occur at high frequencies in particular in electronic control circuits when the phase condition for a negative feedback due to random phase shifts of all components is no longer reliable.

Examples: governor, filling a bucket with a hole in the ground, self-regulating processes in an ecosystem, negative feedback in controllers and amplifiers exposure of beneficial insects, AC motors, heater with thermostat, refrigerator, body heat regulation in mammals, pricing by supply and demand

Examples of variable vibration behavior: predator-prey relationship, rhythm of cortisol secretion, circadian biological rhythms, menstrual cycle, business cycles, control oscillations ( instability) of regulators, self-excitation of amplifiers ( due to inappropriate feedback, inadequate shielding between input and output or mismatched loads )

Stability conditions

The conditions for the stability of the technical system can be treated formal. Clearly, the goal is that the loop gain decreases before a critical phase shift below one.

Details can be found at

• Nyquist criterion
• Complex plane
• Bode plot

Importance of feedback in different areas

Electrical circuitry

In 1913, independently developed Alexander Meissner (* 1883 in Vienna, † 1958 in Berlin) at Telefunken in Berlin and Edwin Howard Armstrong (* 1890, † 1954) in New York, the system of a transmitter and receiver circuit using tube amplifiers with feedback.

1927 found the telephone engineering Harold Stephen Black that it can significantly improve the quality of a signal amplifier, by subtracting a part of the output signal from the input signal, which is a counter-coupling in principle.

Other electrical examples:

• Supercritical positive feedback, even positive feedback of electrical systems for the production of high - or low-frequency vibrations. It is used in oscillator circuits as astable flip-flops and function generators.
• Negative feedback, even negative feedback, electrical systems for the linearization of the frequency response and nonlinear distortions such as the reduction of the distortion factor. Too large a phase delay in the amplifier, the negative feedback can convert into a positive feedback and there are unwanted vibrations.
• Each voltage regulator compares the output voltage with a reference voltage and controls the amplified differential voltage power transmission of a power transistor. Thus, the output voltage is substantially independent of load variations.
• Subcritical positive feedback of resonant circuits for de-attenuation and thus increase the resonance resistance. Applications of this feedback, for example at a Audion. In this, the selectivity, sensitivity and reception quality is increased by the use of feedback, without increasing the number of the most expensive electron tubes having to increase the receiving device.

Sound equipment

In audio engineering or electro-acoustic feedback is (short coupling or " coupling " or "Feedback" called ) a generally undesirable, perceived as an unpleasant whistling self-excitation of the system sound receiver - amp - speakers. Mainly it arises between the fed from the amplifier speakers and microphones. But every other electro- acoustic sound receivers, such as electric guitars or turntables may be affected. A feedback can be formed when a speaker reproduces the signal of a microphone and simultaneously receives the microphone this signal again if it is too close to the speaker, as it typically occurs about hearing aids. The signal is amplified again, played through the speakers, creating an electro-acoustic loop that escalates up to the self-excitation. The frequency of self-excitation is dependent on the frequency-selective properties and the phase shift of the transmission path ( air path, equalizer, speaker, microphone characteristics, reflective chamber walls ) from.

In the extreme case of a feedback in addition to the harassment of the audience and the destruction of the speakers is possible, especially the tweeters can be damaged. Woofers and subwoofers are less sensitive to feedback and also withstand a stronger feedback as a tweeter. Located in loudspeakers crossovers may be damaged.

To avoid coupling with platform, the following measures may help:

• Equalizer with which the PA system during sound check "is whistled " is. It is produced intentionally feedback that can be minimized by a trained technician after hearing with the equalizer or eliminated by those frequencies are lowered, which tend to couple.
• Identify So-called feedback Destroyer ( feedback suppressor ) and automatically suppress building up feedback. The problem is that you can not distinguish between unintentional and intentional feedback and suppress both equally.
• Microphones and speakers can be set up so that between them little direct sound is possible;
• The use of microphones with a suitable directional characteristic ( " kidney" )
• By special arrangement and interconnection of several microphones at the extinction of ambient sound can be effected and so the feedback problem can be reduced ( for example, see Grateful Dead );
• The waiver of microphones by using vibration sensors or electric instruments.
• With Opto Gates unused microphones can be switched off automatically.

Often coupling occurs for an empty audience hall more of a, as in the filled because the listeners absorb sound and its reflection in the room.

The feedback is used deliberately in various modern styles of music, but especially in rock music, particularly in heavy metal as sound design for sound processing.

Furthermore, there are few DJs that incorporate feedback into their performance with. For this purpose, the signal at the headphone output of the mixer is applied to one input. Under extremely cautious use of the various controls ( treble, mid, bass, etc.) noise can thus be generated by distorting whistling to rhythmically slapping and other variations. Every mixer responds to this manipulation differently. Even with minor changes to the controllers may arise abruptly changing noises. , If handled carelessly, as mentioned above, can destroy the boxes

In computer technology

In computer technology feedback can serve to provide the user with information about the current state of an application. This can be done by optical means, such as by color- highlighted details in a graphical user interface. Or it can be used acoustic signals by a sound is played through a speaker. Some input devices have the ability to provide the user with mechanical means feedback. This force feedback is used to make, among other things, the impression of a realistic simulation.

The hardware of many computer games is able to provide the player with mechanical means feedback on events in the game. This is often used for a direct response to the player's actions. One example is vibration of a steering wheel.

A closed control loop with the user as a system block is used in the process of user in the loop, eg mobile communications, smart grid to achieve a demand control.

The Earth System and Climate Research

In the climatology many feedback can be observed. In the ice - albedo feedback (positive feedback ) is reflected for example by freezing more sunlight, so it is colder. This can freeze larger areas and it is even colder. Conversely, the process works well. More feedbacks include clouds, water vapor coupling or the carbon dioxide absorption capacity of oceans. Many of these processes are not yet explored sufficiently accurate and often challenge the meteorological forecasting climate with climate models.

Medicine and Biology

In biology and medicine negative feedback causes the maintenance of homeostasis ( equilibrium state within allowable limits ) of a system. Such processes take place for example starting from regulation in maintaining the body temperature of warm-blooded animals or in the regulation of gene activity.

In contrast, means biofeedback, for example, that a beep or a lamp a value exceeding a measured quantity (eg, skin temperature, muscle tension / tonus or EEG wave amplitude a preselected frequency ) is fed back to the person examined, the otherwise not, or not sufficiently can be perceived. You will be experienced in this way and can serve, for example to learn a self-control.

The human body is a complex system, which is controlled and monitored by a very efficient feedback control system - the central nervous system. The current sensory input is always combined with the matching information ( experiences ) from the memory to provide the individual a suitable future forecast as a policy proposal for the current situation. To be able to react appropriately to any situation immediately. The Brain's proposal is always adapted to the current situation. For example, the brain controls while walking / running after seen optical information about the nature of the way, as you have to put your foot. The feedback system can eg by drugs ( alcohol consumption) to be disturbed; then staggers one or crashes.

Psychology

• In the general psychology of the unconscious perception of their own expressive behavior ( posture, gestures, facial expressions ) and their effect on your own well -being is referred to as feedback. In an experiment by Strack et al (1988 ) describes that the assessment of perceived joke cartoons more higher when subjects activate the typical joy facial muscles.
• In psychology / communication theory Paul Watzlawick (that can be arbitrarily " punctuated " ) with the description of communication circuits which have no beginning and no end, focuses on feedback processes. He speaks of " balanced escalation " or of " complementarity ". This refers to the mutual dependence of the behavior expressions of communication partners that get in the one case by the same court in competition, in the other case confirm themselves in complementary roles to each other or hold.
• A similar concept represents Walter Milowiz in a systemic theory, which he applies primarily to the social work. Here feedback loops and escalating developments in the interaction between people and your environment will be focused as a description for social problems.