I'll get back to you on this one, I'm a little unwell right now, and I need to be in front of my D-50 to tell you what to press.
I would say look for parameters that mention 'velo' if it has a plus (+) figure it will be increasing with higher velocity. If it has a minus figure, the effect will decrease with more velocity.
So if it's in the TVF section, it could effect filter cutoff frequency.
In the TVA section if could be effecting actual note amplitude.
Velocity can effect many D-50 parameters, pitch, for example, but the filter, and amplitude are the usual suspects.
If you want no effect with regard to velocity, I'm sure the parameter should read '0' (zero) - which if you think about it makes sense.
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