ing ▁the ▁first ▁val ve ▁low ers ▁the ▁pitch ▁to ▁A . ▁ ▁De press ing ▁the ▁second ▁val ve ▁in ▁isol ation ▁low ers ▁the ▁pitch ▁to ▁A ▁natural . ▁ ▁But ▁together , ▁these ▁two ▁val ves ▁produce ▁a ▁sharp ▁G ▁natural , ▁because ▁the ▁second ▁val ve ▁slide , ▁which ▁is ▁long ▁enough ▁to ▁length en ▁a ▁B ▁horn ▁to ▁A ▁natural , ▁is ▁slightly ▁too ▁short ▁to ▁lower ▁the ▁longer ▁A ▁horn ▁to ▁G . ▁ ▁Com bin ations ▁using ▁all ▁three ▁val ves ▁have ▁even ▁worse ▁in ton ation , ▁so ▁instruments ▁need ▁some ▁means ▁to ▁compens ate . ▁ ▁Trump ets ▁and ▁fl ugel horn s ▁commonly ▁have ▁s add les ▁or ▁triggers ▁on ▁the ▁first ▁and / or ▁third ▁val ve ▁sl ides ▁to ▁allow ▁length ening ▁of ▁the ▁val ve ▁sl ides , ▁while ▁on ▁larger ▁instruments ▁like ▁the ▁eu phon ium ▁and ▁t uba , ▁such ▁devices ▁are ▁imp ract ical . ▁ ▁Instead , ▁better - quality ▁tub as ▁and ▁eu phon iums ▁are ▁provided ▁a ▁fourth ▁val ve , ▁which ▁takes ▁the ▁place ▁of ▁the ▁ 1 - 3 ▁val ve ▁combination ▁and ▁allows ▁use ▁of ▁ 2 - 4 ▁in ▁place ▁of ▁ 1 - 2 - 3 . ▁ ▁Better ▁manufact ur ers ▁of ▁three - val ve ▁instruments ▁such ▁as ▁S ous aph ones ▁often ▁make ▁the ▁third ▁val ve ▁slide ▁long ▁enough ▁to ▁partially ▁address ▁this ▁def ic iency . ▁ ▁Also , ▁many ▁t uba ▁models ▁place