Voicing procedure is a highly acquired skill, so when do you actually need a voicing service and what is voicing service?
When you feel that your piano tonal quality is not even, too soft or too harsh, then you probably need the voicing service to equalize the tone and there are commonly 2 ways of voicing a piano, where we either voice UP or voice DOWN. However, before we jump into the voicing procedure, first we need to make sure that your piano is in a tip top condition, where a good regulation must be achieved, a good repair (if necessary), a stable concert tuning, then we finally make the judgement before voicing.
Oh yeah! The "voice" of your piano sometime can be affected by the surrounding environmental acoustic as well, the sound can also be changed by the fluctuation of humidity level too.