# What is power spectral density?

I want to know the exact meaning of power spectral density, by a suitable real life example. There are a lot of definition but how can I correlate it with real experiences?

I want to know the exact meaning of power spectral density, by a suitable real life example. There are a lot of definition but how can I correlate it with real experiences?

## Popular Answers

Light Coherence· Indian Institute of TechnologyPower spectral density function (PSD) shows the strength of the variations(energy) as a function of frequency. In other words, it shows at which frequencies variations are strong and at which frequencies variations are weak. The unit of PSD is energy per frequency(width) and you can obtain energy within a specific frequency range by integrating PSD within that frequency range. Computation of PSD is done directly by the method called FFT or computing autocorrelation function and then transforming it.

Go here for more...

http://www.cygres.com/OcnPageE/Glosry/SpecE.html

Taha A. Ali· Arab Academy for Science, Technology & Maritime TransportPower spectral density function (PSD) shows the strength of the variations(energy) as a function of frequency. In other words, it shows at which frequencies variations are strong and at which frequencies variations are weak. The unit of PSD is energy per frequency(width) and you can obtain energy within a specific frequency range by integrating PSD within that frequency range. Computation of PSD is done directly by the method called FFT or computing autocorrelation function and then transforming it.

http://www.cygres.com/OcnPageE/Glosry/SpecE.html

## All Answers (34)

Andrea Aprovitola· Scuola Politecnica e Delle Scienze di BaseNirav Desai· Symbiosis Institute of Computer Studies and ResearchNirav Desai· Symbiosis Institute of Computer Studies and ResearchAndrea Aprovitola· Scuola Politecnica e Delle Scienze di BaseNirav Desai· Symbiosis Institute of Computer Studies and ResearchAndrea Aprovitola· Scuola Politecnica e Delle Scienze di BaseNirav Desai· Symbiosis Institute of Computer Studies and ResearchNirav Desai· Symbiosis Institute of Computer Studies and ResearchNirav Desai· Symbiosis Institute of Computer Studies and ResearchNirav Desai· Symbiosis Institute of Computer Studies and ResearchNisha Bhatt· Amrapali Group of InstitutesNirav Desai· Symbiosis Institute of Computer Studies and ResearchNisha Bhatt· Amrapali Group of InstitutesNisha Bhatt· Amrapali Group of InstitutesDaoud Berkani· National Polytechnic School of AlgiersFouad Mohammed Abbou· Al Akhawayn UniversityPower spectral density describes the signal power distribution over the frequency.

Aasim Khurshid· Universidade Federal do Rio Grande do SulPower spectral density is distribution of power, and it can be calculated by Fourier Transform of auto-correlation function of the signal. You can test this to better understand. Take a signal/image, find auto-correlation and take FFT, plot it.

Taha A. Ali· Arab Academy for Science, Technology & Maritime TransportPower spectral density function (PSD) shows the strength of the variations(energy) as a function of frequency. In other words, it shows at which frequencies variations are strong and at which frequencies variations are weak. The unit of PSD is energy per frequency(width) and you can obtain energy within a specific frequency range by integrating PSD within that frequency range. Computation of PSD is done directly by the method called FFT or computing autocorrelation function and then transforming it.

http://www.cygres.com/OcnPageE/Glosry/SpecE.html

Daoud Berkani· National Polytechnic School of AlgiersThe power spectral density shows how the energy of a signal is distributed. That can allow us to make some decisions or operations on a considered signal. The important thing is that the DSP can be obtained from the function of auto correlation without signal priory knowledge (Wiener-Khintchine theorem 1929). What makes the valid FT for a signal is random or real.

Ahmed Guerine· Institut National des Sciences Appliquées de RouenHi

I advice you to see these documents. You will find what you need with some examples.

Best regards

Chirag Pallan· Indian Institute of Technology Madraswhen you measure the signal it will be having the various frequency components in it, since the power contained in each signal with different frequency will be different so the psd is the graph of power vs frequency.

also the main application of the psd plot is that it will give the range of the frequency where the power density is high

hope this will satisfy your question

Light Coherence· Indian Institute of TechnologyGo here for more...

http://www.cygres.com/OcnPageE/Glosry/SpecE.html

S. Bali Reddy· Indian Institute of Technology GuwahatiPower spectral density function shows the energy with frequency. It will useful when you want check the signal is week or strength.

Yves Chapron· Alpine Institute of Environmental DynamicsWhat is the difference between a PSD = f( Hz) and the square of energy (E^2) = f(Hz)?

When a domain in Hz is changing in energy (increase of E^2) maintained along all the signal following. In other words what is the difference in the meaning of density (PSD) versus only the square of E (E^2) = Hz?

What is lost in the information relatively

Ahmed Guerine· Institut National des Sciences Appliquées de RouenHi

Power Spectral Density ou PSD is the square of the Fourier transform module, divided by the integration time T (or, more strictly, the limit as t goes to infinity of the mathematical expectation of the square of the Fourier transform module signal - this is called average power spectral density). Thus, if x is a signal X and its Fourier transform, the spectral power density is:

PSD=ІXІ^2/T

Best regards

Sumit Balguvhar· Indian Institute of Technology DelhiPSD means how the strength of a signal is distributed in the frequency domain.

Yusuf Adinegoro· Queensland University of TechnologyI have the a similar question, I'd like to add more questions, anyone had experienced to analyze the from Z-accelerometer to PSD and road roughness (IRI). Thanks

Hemlata Dhoundiyal· Indian Institute of Technology DelhiHow can we define the PSD in lower frequency or in 1/f noise case.

Daoud Berkani· National Polytechnic School of AlgiersStrongly, the PSD is the Fourrier transform of the signal auto correlation (Wiener/ Kintchine 1929) that makes possible to extend or to use the Fourrier transform for real signals or stochastic process

Chintan Joshi· Florida International UniversityIn power density spectrum (MV^2/Hz) graph, it is seen that some power values at certain frequency indicates negative value(below zero). What does this signify? Can power values be negative?

Daoud Berkani· National Polytechnic School of AlgiersThe DSP can not be negative. Maybe you should normalize your signal before calculating the DSP.

Chintan Joshi· Florida International UniversityI am processing my data in EEGlab and in power spectrum density I could se values above 30hz to be in the range of (-7 to 7) mV^2/hz. I am attaching a paper over here to let everyone better understand. This paper too has PSD negative for some values.

## Article: Occipital gamma activation during Vipassana meditation. Cognitive Process, 11, 39-56

ABSTRACT:Long-term Vipassana meditators sat in meditation vs. a control rest (mind-wandering) state for 21 min in a counterbalanced design with spontaneous EEG recorded. Meditation state dynamics were measured with spectral decomposition of the last 6 min of the eyes-closed silent meditation compared to control state. Meditation was associated with a decrease in frontal delta (1-4 Hz) power, especially pronounced in those participants not reporting drowsiness during meditation. Relative increase in frontal theta (4-8 Hz) power was observed during meditation, as well as significantly increased parieto-occipital gamma (35-45 Hz) power, but no other state effects were found for the theta (4-8 Hz), alpha (8-12 Hz), or beta (12-25 Hz) bands. Alpha power was sensitive to condition order, and more experienced meditators exhibited no tendency toward enhanced alpha during meditation relative to the control task. All participants tended to exhibit decreased alpha in association with reported drowsiness. Cross-experimental session occipital gamma power was the greatest in meditators with a daily practice of 10+ years, and the meditation-related gamma power increase was similarly the strongest in such advanced practitioners. The findings suggest that long-term Vipassana meditation contributes to increased occipital gamma power related to long-term meditational expertise and enhanced sensory awareness.Mahmud Naraqi· Ahvaz Jondishapour University of Medical Sciencesdear Chintan

I think you mean " power 10*log(10) (uv^2/Hz)" . I am right?

this is logarithm scale and every negative value of this scale in the real aspect, is a number between 0 & 1. in this range every log is negative but the PSD is positive and in [0 1] range

Can you help by adding an answer?