# [Eeglablist] EEG AC and DC record problem

Manish Arora openmeddev at gmail.com
Tue Jul 7 06:24:57 PDT 2015

```Hi Booer,

If you applied flowing transformation /normalization :

y[i]= 2*(x[i] -x_mn)/ (x_max- x_min) -1

then resultant signal y[i] will be with zero mean and range between -1 and
+1. Here x_mn,  x_max and x_min are mean, max and minimum of the signal.
You can apply the same transformation on both AC and DC signal.

If the origin of the AC and DC signal is same and there are no frequency
dependents filter in obtaining AC signal, the resultant should be
identical.

Regards,
Manish

Manish Arora

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www.openmeddev.net/blog

On 7 July 2015 at 18:19, bjj2909102003 <bjj2909102003 at 163.com> wrote:

> Thank you, Manish.
> I tried your method. But I don't  ensure that this simple normalization
> in DC data is equal to AC record. Actually, I found they were not equal.
> And it will affect my model (based on AC record data) applying into the DC
> record data.
> I guess AC record data is from DC record data. But I don't know what  the
> calculation process is .
>
> Regards,
> Booer
> ------------------------------
> bjj2909102003
>
>
> *From:* Manish Arora <openmeddev at gmail.com>
> *Date:* 2015-07-07 01:19
> *To:* bjj2909102003 <bjj2909102003 at 163.com>
> *Subject:* Re: [Eeglablist] EEG AC and DC record problem
> Hi Booer,
>
> I don't know if  I understood your requirements completely, but you can
> recenter the DC mode data around zero by subtracting simply subtracting
> mean of the signal from each data point.
>
> Regards,
> Manish
>
> Manish Arora
>
> Open Medical Devices                         Like us on Facebook
> fb.com/openmeddev
> www.openmeddev.net/blog
>
>
> On 6 July 2015 at 19:18, bjj2909102003 <bjj2909102003 at 163.com> wrote:
>
>> Hi, everyone.
>> Recently, I recorded my EEG data in AC mode. And I made the model based
>> on AC mode data (range centred around zero). Now I want to analyze
>> on-line EEG data by my previous model. But the online data is acquired in
>> DC mode (value is big and not centred around zero) by access SDK. I
>> don't know how to convert DC mode data into AC mode data so that I can
>> apply the previous model into the data?
>>
>> Thank you.
>> Booer
>>
>> ------------------------------
>> bjj2909102003
>>
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