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'Wednesday's rehearsal will now be strings only.' The text message from the Assistant Orchestra Manager said. 'Oh, deep joy....' was the response from my fiddle-playing drinking companion as we looked at each other over our pints and pinging mobile phones. Truth is, string sectionals are actually quite useful, not just because we viola players need extra help but also so we can configure and synchronise bowings and sort out the inevitable tricky bits this orchestra seems to delight in. The downside is that they can leave one a lot more exposed as there is no 'covering fire' from our colleagues who blow and bang things.

My day had already started badly: the shower refused to work, my 10-year-old daughter burst into tears because she didn't want to go to school and due to all the fluffy white stuff falling from the sky, Southeast Trains were being awkward. I shivered in to Ö÷²¥´óÐã Studio 1 Maida Vale at 11 o'clock for a 10.30 start. Now it's pretty much the first thing one learns at college is that you can't be late for a rehearsal, but being the insane optimist that I am, I work on the principle that if I am late somebody else will be too and it won't be so bad. I was only partly wrong - the Principal viola was also stuck.

Now when that happens the next in line shuffles up to fill the gap and so on down the line, (all very hierarchal, rather like the Army). So, as I defrost I am hastily looking through the part to see if there are any four-letter words (that's 'Solo') that I need to look at. Beside me now sits our new No.4 violist, Carol Ella. (Carol is great fun and has a thing about turnips... don't ask me why). A decision is made to delay the start of the rehearsal.

Oliver Knussen is conducting and is quite relaxed as further stragglers enter the studio. Like his compositions he is an incredibly fastidious conductor with acute hearing. I'd say that along with Pierre Boulez and George Benjamin he's got some of the best lugs in the business. That means he doesn't miss a trick and he searches continually for the right colour and balance... and also the right notes! Olly has had a long association with the orchestra - both his father and brother were once members of the double bass section and last year he became our Artist-in-Association. We have always enjoyed playing his finely-honed pieces and the many (if on occasion rather esoteric) concerts he has put on with us. He holds the orchestra in high esteem and is seldom without humour - 'Could the violas try and make it sound less like a dog grabbing a bone?' he asks respectfully. 'This bit sounds like Les Dawson playing Strauss..." My 10-year-old also likes him, but only because she thought it was Hagrid conducting us on TV.

Henze generally writes extremely well for the orchestra; only for some reason best known to himself, I suspect that, sometime in the 1970s, he decided to change the way he notates his music. Instead of having accidentals (sharps and flats) pertaining throughout the whole bar, they apply only to each individual note. This means that if, for example, he writes a string of repeated semiquaver E flats, he writes a flat sign in front of each semiquaver. That can leave a bar with more flats than a Peckham Council Estate and, frankly, it's confuse-a-cat timeÌýfor the player.

Add to that, that it's different to the system we all know and love, and you can have a few problems reading the dots. Well, even more problems... Maybe when Hans turns up this weekend I'll pluck up the courageÌýto ask him why he does it.

Gradually, the unfamiliar notes become more familiar and the string lines emerge, the co-principal viola arrives in time to play the solos, and the day is salvaged. I leave the studio wondering how the piece will sound with our wind and percussion colleagues and also if Southeast Trains are working... they aren't. I look around a deserted London Bridge station for someone to blame, then I notice today is the 13th... that'll do.

• Phil Hall is sub-principal viola of the Ö÷²¥´óÐã Symphony OrchestraÌý

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