# NaN in alpha frequency band

**URL:** <https://mne.discourse.group/t/nan-in-alpha-frequency-band/3723>\
**Category:** Support & Discussions\
**Tags:** time-frequency, eeg\
**Created:** [September 22, 2021, 2:24pm UTC](https://mne.discourse.group/t/nan-in-alpha-frequency-band/3723 "2021-09-22T14:24:22Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![talhaanwarch](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/talhaanwarch/32/813_2.png) [@talhaanwarch](https://mne.discourse.group/u/talhaanwarch)\
**Post date:** [September 22, 2021, 2:24pm UTC](https://mne.discourse.group/t/nan-in-alpha-frequency-band/3723/1 "2021-09-22T14:24:22Z")

</div>

Data load

```python
data=mne.io.read_raw_cnt('data.cnt',preload=True)
data.drop_channels(['A1','A2','NC', 'X1', 'X2', 'X3', 'X4'])
data.set_montage('standard_1005',match_case=False)
data.set_eeg_reference()

```

Power spectral density  
`data.plot_psd(fmin=0.2, fmax=45);`

 ![image](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/b4f82808c55ca6536f919032f9c4de36bc57c5c5.jpeg)

When i try to get alpha band like this

```python
from mne.time_frequency import psd_welch
psds, freqs = psd_welch(data, fmin=0.2, fmax=45)
psds /= np.sum(psds, axis=-1, keepdims=True)
psds_band = psds[:, (freqs >= 8.5) & (freqs < 11.5)].mean(axis=-1)
psds_band

```

I got NaNs. Though there is no NaNs in other frequency bands. Any idea

---

<div class="post-metadata">

**Author:** ![richard](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/richard/32/15_2.png) [@richard](https://mne.discourse.group/u/richard)\
**Post date:** [September 22, 2021, 2:46pm UTC](https://mne.discourse.group/t/nan-in-alpha-frequency-band/3723/2 "2021-09-22T14:46:15Z")

</div>

Hello @talhaanwarch, could you share the data you used?

---

<div class="post-metadata">

**Author:** ![talhaanwarch](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/talhaanwarch/32/813_2.png) [@talhaanwarch](https://mne.discourse.group/u/talhaanwarch)\
**Post date:** [September 22, 2021, 8:05pm UTC](https://mne.discourse.group/t/nan-in-alpha-frequency-band/3723/3 "2021-09-22T20:05:59Z")

</div>

Hi, @richard please download it from here

> **[data.cnt](https://drive.google.com/file/d/1PLfXWwbImm5UZ7uPtK-gqcAsRYZLvFkC/view?usp=sharing)**
>
> Google Drive file.

---

<div class="post-metadata">

**Author:** ![richard](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/richard/32/15_2.png) [@richard](https://mne.discourse.group/u/richard)\
**Post date:** [September 25, 2021, 11:09am UTC](https://mne.discourse.group/t/nan-in-alpha-frequency-band/3723/4 "2021-09-25T11:09:27Z")

</div>

If you look at `freqs`, you’ll find that it’s

```python
array([ 3.90625, 7.8125 , 11.71875, 15.625 , 19.53125, 23.4375 ,
       27.34375, 31.25 , 35.15625, 39.0625 , 42.96875])

```

So the requested frequencies that satisfy

```python
(freqs >= 8.5) & (freqs < 11.5)

```

do not exist.

If you pick a different frequency band, like 8–12 Hz, it works.

Best wishes,  
Richard