There will be natural variations in volume between readers. Reject only if the volume is so high that the recording breaks up, or (more commonly) if it is so low that you can’t hear what is being said without reference to the written text.
Bolumen aldaketa naturalak egongo dira irakurleen artean. Baztertu grabaketa bakarrik bolumena hain handia bada grabazioa eten egiten dela edo (ohikoagoa dena) hain baxua bada, ezin dela entzun esaten dena testu idatziari erreferentzia egin gabe.