The orchestra provides invaluable support to the singers. But what do the players think? Horn player Ian Fisher shares their secrets.
Everyone has an opinion about which singer should win the competition: the enthusiastic audience in the hall; the inscrutable judges; the television viewers; the professional pundits; everyone. Even the orchestra.
However, our assessment is more difficult to make because the singers perform facing away from us which means we don't receive the full effect, especially where I sit at the back of the stage.
It is true that we will have got to know the contestants a little in rehearsal but it's the concert performance that counts and on the night there are many variables that come into play. Someone who has seemed a sure winner in the run-through may fade on the platform and an apparent shrinking violet when practising could blossom in the glare of the lights. That's the magic of live performance.
Discussion within the orchestra will throw up different criteria for what constitutes a possible winner. Depending on who you talk to, the deciding factor could be vocal range, tone quality, versatility or bust measurement. Whatever the reason, players can become fiercely supportive of 'their' singer and may disagree passionately with the judges' decision.
Of course, there is no link between this passion and the fact that there is often an orchestral flutter on the result in the form of a sweepstake (I've never taken part because horn playing is enough of a gamble for me; try making a living by blowing raspberries down a coiled up length of brass tubing and you'll see what I mean).
I suppose having a (tiny) financial interest in the winner could be considered a conflict of interest but there is little that players can do to try to influence the outcome apart from vigorously applauding a favoured performer while smiling enthusiastically at the jury.
As musicians, we all know how difficult it can be to make a career out of performing and are consequently extremely supportive of anyone willing to put themselves through the necessary rigours to get there.
Conductors, too, generally go out of their way to ensure the competitors give of their best. Most of the singers are in the early stages of their careers and perhaps lack the experience that will come with time. Under these circumstances, the most sympathetic conductors attempt to nurture latent talent by offering helpful suggestions that can give guidance without swamping the soloist's own personality or ideas.
The limelight clearly belongs to the competitors but occasionally the chosen programme includes something exposed for an orchestral musician. It is on such occasions that we are thankful for the team of Cardiff Singer librarians who give a timely warning to us of any potentially tricky piece before it appears at the dress rehearsal.
And I guess that sums up the whole competition. There can only be one winner but to get there he or she relies on the collaborative effort of us all, just as we rely on each other. And, for me, that is what music making is about.
Ian Fisher joined the horn section of the BBC National Orchestra of Wales in 1986, so has taken part in all except the first two competitions, playing for hundreds of competitors.