Spectrogram: find the median of the power (dB) to plot with median threshold

I have a spectrogram:

 [s,w,t] = spectrogram(signal,blackmanharris(windLength),overlap,NFFT,fs,'yaxis');

and I want to plot it with a threshold represented by the median of the dB band, like this:

 spectrogram(signal,blackmanharris(windLength),overlap,NFFT,...
                fs,'yaxis', 'MinThreshold', median_dB)

How can I calculate the 'median_dB' so that it represents the median of the power/frequency vector?

I started with

 s = abs(s);
 s_dB = 10*log10(s);
 threshold = median(s_dB)

s is actually a matrix and I do not seem to fully understand what the function does. Where do I go from here? Any help would be greatly appreciated!