# [Eeglablist] Power spectrum

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Thu Feb 9 19:46:44 PST 2017

```Dear Laxmi,

I can't agree with you any more. You can also make money and cure disease,
only if you know how to use it!

Makoto

On Tue, Feb 7, 2017 at 8:23 PM, Laxmi Shaw <laxmi.shaw22 at gmail.com> wrote:

> Use Matlab. U can easily calculate PSD
>
> On Wed, Feb 8, 2017 at 7:44 AM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> wrote:
>
>> Dear Leonardo,
>>
>> > 1- The code that you recommended computes power spectrum in "10*log10(uV^2/Hz)".
>> In this case, can we consider this unit without Hz (i.e., only 10*log10
>> (uV^2))?
>>
>> It is called power spectrum density (PSD). It means whatever power *per
>> second*. Hence you have Hz in the unit. If it is not per second, 20 s
>> long data would have twice as large power than 10 s long data. So you can't
>> remove Hz from the unit to show what you exactly mean.
>>
>> > 2- In fact, my major aim is computing power spectrum in "uV^2" unit,
>> and the code you recommended does different thing--it, actually, computes
>> power spectrum in power spectrum in unit "10*log10(uV^2/Hz)" (please see
>> the attached file). Kindly, could you guide me to way of computing the
>> power in "uV^2" unit ?
>>
>> Again, if you remove Hz, then you multiply the power spectrum by data
>> length in second. You don't want to do it. If you want to convert it from
>> log scale to linear scale, use 10^(x/10)
>>
>> > 3- Is there any formula that converts power spectrum from "10*log10(uV^2/Hz)"
>> unit into "uV^2" unit?
>>
>> Again, 10^(x/10) but you still want to do uV^2/Hz, otherwise you can't
>> compare data with different lengths.
>>
>> Makoto
>>
>>
>> On Thu, Feb 2, 2017 at 5:46 PM, Leonardo Lion <llionname at gmail.com>
>> wrote:
>>
>>> Dear Makoto,
>>>
>>> Thank you so much for your help.
>>>
>>> I have two main issues:
>>>
>>> 1- The code that you recommended computes power spectrum in "10*log10(uV^2/Hz)".
>>> In this case, can we consider this unit without Hz (i.e., only 10*log10
>>> (uV^2))?
>>>
>>> 2- In fact, my major aim is computing power spectrum in "uV^2" unit, and
>>> the code you recommended does different thing--it, actually, computes power
>>> spectrum in power spectrum in unit "10*log10(uV^2/Hz)" (please see the
>>> attached file). Kindly, could you guide me to way of computing the power in "uV^2"
>>> unit ?
>>>
>>> 3- Is there any formula that converts power spectrum from "10*log10(uV^2/Hz)"
>>> unit into "uV^2" unit?
>>>
>>> Kind regards,
>>> Leonardo
>>>
>>>
>>> ​
>>>  power.png
>>> ​
>>>
>>> On 3 February 2017 at 02:08, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
>>> wrote:
>>>
>>>> Dear Leonardo,
>>>>
>>>> See my wiki page for the example code. Unfortunately, you can't do this
>>>> from GUI.
>>>> https://sccn.ucsd.edu/wiki/Makoto%27s_useful_EEGLAB_code#How
>>>> _to_extract_EEG_power_of_frequency_bands
>>>>
>>>> Makoto
>>>>
>>>> On Tue, Jan 31, 2017 at 9:25 AM, Leonardo Lion <llionname at gmail.com>
>>>> wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> How to convert the EEGLAB power spectrum "10*log10(uV^2/Hz)" into "
>>>>> uV^2" only?
>>>>>
>>>>> Thanks.
>>>>> Leonardo
>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Makoto Miyakoshi
>>>> Swartz Center for Computational Neuroscience
>>>> Institute for Neural Computation, University of California San Diego
>>>>
>>>
>>>
>>
>>
>> --
>> Makoto Miyakoshi
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
>>
>> _______________________________________________
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>>
>
>
>
> --
> Laxmi Shaw
> Research Scholar(PhD)
> IIT Kharagpur
> West Bengal
> Ph no-08388837821
>
>

--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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