Fiddler Alasdair Fraser stands in front of his congregation of pupils, violin in hand.

Pacing slowly back and forth like an old and dangerous lion, he says: "I want to remind you how powerful this instrument is." We sit, spellbound. "The fiddle is so potent, priests used to have them burnt."

We are crammed in to the elegant and bright space of Studio 1 at Glasgow's City Halls for a masterclass that is part of this year's Celtic Connections programme. Not a likely place to start a fiddle revolution perhaps, but we've come in droves. It's a familiar space to me, through working here every week with the Scottish Chamber Orchestra. The men at the front desk assume I'm here to teach the workshop, but I'm not. I'm here to learn, and we're not long into Fraser's opening address before I realise I'm going to learn a lot more than just some tunes.

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It's a crowd of all ages, from children to grandparents. Big fiddles (cellos) jostle for space too. I'm told next year there will also be ukuleles. Next to me is Rob, 30, with his father, Dick. Rob is about to go away to work in the Antarctic for five months and tells me sadly that he's not allowed to take his fiddle, so father and son have come along for a farewell tune.

Everyone in the "fiddle village" seems to be here to have fun and feel creative. Some people get up and dance in the middle of a tune, even the lady who just got a new knee. Nobody is hung up on minor details such as tuning. In fact no-one tunes up strings at all, apart from me. Neither are they bothered that Fraser forgets to call a break on the first day, because the group is in such a state of flow. To my horror, I find myself checking my watch at exactly the time we would call a break in an orchestra rehearsal, and worry about how institutionalised I have become before I am drawn back into the music.

This way of learning tunes – repeating over and over again until they're in your fingers, not stopping to correct any mistakes, but just having another go when that bit comes round again – is typical of a folk style of learning. Fraser encourages us, saying he wants "to see the room fill up with mistakes". Somehow, playing the same tune thousands of times doesn't get boring. I shut my eyes, committing the tunes to memory, finding shapes to pin to my mind. I become so lost in the meditative repetition I don't notice when everyone else has stopped, and I'm left playing on my own.

We move on to learn new techniques like "chopping". I don't seem to be very good at this. No matter how hard I try, landing the bow on my strings doesn't seem to make that scratchy, if funky, sound that is being demonstrated by cello tutor Natalie Haas. On to ornaments: Fraser takes us through the many options and, as usual, I despair of my slow trill. But then I notice the way he is throwing his fingers loosely onto the strings for the trill, rather than heavily placing them. And I try it. Eureka! My twiddles are as fast as I could possibly hope for.

"Some people have what I like to call a presbyterian fear of the ornate," Fraser's slow but intent delivery comes at us. "Some people are actually afraid to put in grace notes." I remember my questions when working with folky friends, about whether there were rules about where to put grace notes, and not to put them, like there are in classical music. How amused those guys were at my fear of breaking musical rules.

Fraser's most impassioned exhortation to us is to find our own voice in our music. "Some of us have been cleaned up. Some of us have had our language taken away from us. What do you speak with your fiddle? Is it Gaelic, Doric, Glasgow?" After each weighty sentence, he plays. Sure enough, the messages go in deeper that way. The phrases come out of his fiddle like a sorcerer casting phantoms. He conjures hot Grappelli jazz, old-style Menuhin, elegant baroque, lamenting Gaelic song, dangerous Strathspeys – all of them with a rhythm and expression that makes my jaw drop. When he talks of keeping a room of 300 people up dancing til 5am, with just a fiddle, there's a gasp of awe, but we believe him.

During the break, I come across Ruairidh Geddes, a 13-year-old, ripping into new tunes. He's wearing a Royal Conservatoire T-shirt with pride, and studies traditional music there. He tells me he was so inspired by Fraser's week-long summer fiddle course at Sabhal Mor Ostaig, on Skye, that he had to come to the RCS. Leila Cruickshank, also 13, sits next to him. She tells me they are friends, though she does more classical violin. The thing was, she explains, she had always been a bit better than Geddes, but after he came back from Skye, he was suddenly better than her. They laugh together, revealing matching braces. "So that's why I'm here" she says, "Because I had to keep up."

You said it, Leila. You and me both.