In order to refine playback in capella, capella-tune offers the option to set up many details. Exactly how loud should a mezzoforte be? How quiet a pianissimo?
On the Dynamics & Rhythm tab you can set individual values via slide control or by entering numerical values:
The box "Include dynamics during playback" must be ticked.
And vice versa: If you do not want any dynamic change, remove the tick.
More important information: Where is capella-tune?