Noise in electronic components

All components that are used in electronics suffer from noise production and that noise is said to be thermal noise that adds up with the signal that passes through the component.

In electronics circuits there are two main types of noises: voltage noises and current noises.
Voltage noises add a voltage waveform to the signal and current noises add a current waveform to the signal that also becomes voltage waveform if that current is passed through a component.

Let as summarize the types of noise that are frequently present in audio equiment in terms of distributions:

• White noise: has equal power in all frequency ranges and has a gaussian distribution. This type of noise is the dominant in audio electronics and is created mainly by the heated components.
• Red noise: it is a Brownian type of noise and its energy decreased 6dB per octave. It is more prevalent in the low frequencies and is not created by discrete components as resistors, BJTs, etc. It is present thow in oscillators used in synthesizers.
• Pink noise: has equal power in equal ratios of bandwidth. For example pink noise has equal power at range [200Hz,400Hz] and  at [400Hz, 800Hz]. Its power decreased 3dB per octave as frequency increases.
• Blue noise: power increases 3dB per octave as frequency increases
• Purple noise: power increases 6dB per octave as frequency increases

 These are general types of noises and below are some other forms that are present in audio circuits:

Johnston noise: is a form of white noise and is the kind of noise created by almost all electronics components that have inherent ohmic resistivity. It is most prevalent in resistors. Transistors for example have also Johnson noise because of their ohmic resistance at the base (rbb) . Johnston noise is a voltage noise and its density is given by the following equation: $$ \bar{v}_{n}=\sqrt{4kTRB} $$

where, k is the Boltzmann's constant, T is the environmental temperature in Kelvin R is the ohmic resistivity  of the component in Ohms and B is the bandwidth of the signal

Capacitors do not suffer from Johnson noise due to their reactance of capacitance. It cancels out the noise produced by their inherent ESR.

The resistor is the component that suffers most from Johnson noise and the larger its ohmic value the larger the noise induced. If it is avoidable to use a smaller resistor value then resistors with higher power rating are usually used. Larger power rating means lower noise (of course for a quality resistor).

The table below gives a list of resistor values and their Johnson noise.

Shot noise: this noise is a current noise and is correlated to the moving charge inside a conductor. It is correlated with the space that the charge is gathered, rather than the current value in Amperes. Furthermore, research has proven that small currents suffer most from that kind of noise.
It is a significant noise in Bipolar Junction Transistors when operated at small collector currents.
The following equation gives the density of this noise: $$ \bar{i}_{n}=\sqrt{ZqI_{DC}B} $$

where, Z is the ohmic impendance of the component that the current passes through, q is the charge of the electron, Idc is the mean value of the signal and B is the bandwidth.

1/f noise (Flicker noise): as implied by its name it is decreased as frequency is increased and is prevalent in low frequencies, where the AC waveform of the signal comes closer to DC (alters with at smaller rate).

Popcorn noise: This type of noise is produced by semiconductors, due to heavy metal ion contamination in their materials (Gold). Measurements with such noise are used to determine the quality of a semiconductor. The distribution of this noise is not Gaussian.