Hi,

I’m getting a value error when I run my epochs through psd_welch().

- MNE version: e.g. 0.24.0
- operating system: Windows 10

```
ValueError Traceback (most recent call last)
<ipython-input-104-243081137e4d> in <module>
1 kwargs = dict(fmin=2, fmax=40, n_jobs=None)
----> 2 psds_welch_mean, freqs_mean = psd_welch(epochs, average='mean', **kwargs)
3 psds_welch_median, freqs_median = psd_welch(epochs, average='median', **kwargs)
4
5 # Convert power to dB scale.
<decorator-gen-256> in psd_welch(inst, fmin, fmax, tmin, tmax, n_fft, n_overlap, n_per_seg, picks, proj, n_jobs, reject_by_annotation, average, window, verbose)
c:\users\user\appdata\local\programs\python\python37\lib\site-packages\mne\time_frequency\psd.py in psd_welch(inst, fmin, fmax, tmin, tmax, n_fft, n_overlap, n_per_seg, picks, proj, n_jobs, reject_by_annotation, average, window, verbose)
253 n_overlap=n_overlap, n_per_seg=n_per_seg,
254 average=average, n_jobs=n_jobs, window=window,
--> 255 verbose=verbose)
256
257
<decorator-gen-255> in psd_array_welch(x, sfreq, fmin, fmax, n_fft, n_overlap, n_per_seg, n_jobs, average, window, verbose)
c:\users\user\appdata\local\programs\python\python37\lib\site-packages\mne\time_frequency\psd.py in psd_array_welch(x, sfreq, fmin, fmax, n_fft, n_overlap, n_per_seg, n_jobs, average, window, verbose)
143 # Prep the PSD
144 n_fft, n_per_seg, n_overlap = _check_nfft(n_times, n_fft, n_per_seg,
--> 145 n_overlap)
146 win_size = n_fft / float(sfreq)
147 logger.info("Effective window size : %0.3f (s)" % win_size)
c:\users\user\appdata\local\programs\python\python37\lib\site-packages\mne\time_frequency\psd.py in _check_nfft(n, n_fft, n_per_seg, n_overlap)
45 'n_times. If you want zero-padding, you have to set '
46 'n_per_seg to relevant length. Got n_fft of %d while'
---> 47 ' signal length is %d.') % (n_fft, n))
48 n_per_seg = n_fft if n_per_seg is None or n_per_seg > n_fft else n_per_seg
49 n_per_seg = n if n_per_seg > n else n_per_seg
ValueError: If n_per_seg is None n_fft is not allowed to be > n_times. If you want zero-padding, you have to set n_per_seg to relevant length. Got n_fft of 256 while signal length is 91.
```

Can someone help me resolve this error?

Thanks