Last night’s Hilliard Ensemble concert, in Budapest’s magnificent Vigadó concert hall, was thoroughly different from anything in my concert-going experience.  For a start, there’s the line up: a male vocal quartet of one countertenor, two tenor and baritone. And I don’t suppose there are many - if any - ensembles who will, in a single concert, perform music ranging from Gregorian chant to contemporary, from England to Armenia, with many points in between.

These surface facts, however, mask the key thing that made this concert so different: the intent of the programme. Whether they are singing a recent choral composition or chants from a mediaeval hymnal, with just a few exceptions, this is a performance devised to place you in a state of altered consciousness – something akin to the state, no doubt, that those Gregorian monks would have hoped to achieve through meditation and prayer.

The effect is achieved by vocal technique that is both distinctive and impressive. All four voices are extremely pure: the notes are clean and perfectly level, without the slightest hint of vibrato. The dynamic range is very compressed, apart from those delicious moments when a countertenor voice soars above the others. By some combination of innate quality and technical effort, the four voices have very similar timbre: when baritone Gordon Jones sang a solo, it struck me that this sounded exactly like a typical countertenor voice, just in a lower register.

Attack and release on most notes are very gentle, reminding me of the way an electric guitarist will use a swell pedal to make a note rise to full strength out of nothingness, with no discernible breakpoint. So you couldn’t hear much in the way of consonants, and for all but a few numbers, words were unintelligible. But then, I don’t imagine anyone was expecting a Budapest audience to be fully conversant with English, Latin and Armenian, and lyrics or descriptions of individual numbers were conspicuously absent from the programme.

In other words, very little in this concert was allowed to get in the way of its basic intent: to reach directly into your innermost being with sheer purity and beauty of voice.

When I say “very little”, that’s because there were notable exceptions to much of what I’ve written above. For example, the short opening number, Mundus vergens in defectum, and the long closing number, Viderunt omnes, were altogether more upbeat, with marked dance-like rhythms and a much more folky feel - it made me realise how closely interwoven are the two genres of choral music and traditional English folksong.

The other numbers that didn’t fit the pattern were two works by Arvo Pärt. Most Holy Mother of God, which closed the first half, was definitely sung to be understood, as well as being theatrical and full of dynamic contrast. Pärt’s music may depart from modes or major scales in a way that the more ancient works do not, but those departures are used sparingly and in a way that brings real impact. There was a baritone solo of rare beauty, and the last line, preceded by a sharp moment of silence, was sung with a huge step-up in intensity: a real tour de force. And one of the Pharisees, in the middle of the second half, shared the same theatrical quality, reenacting the Bible scene with force and urgency. It also shared the greater emphasis on word setting, with some breathtaking effects. If you find a recording of this, listen out for the “oint” of “anointed his feet with the ointment” after a repeated plainsong note, or the “Je” of “And Jesus answering said unto him”: these are individual syllables of immense power.

For me, the Pärt pieces were the highlight of the concert, although And one of the Pharisees sat rather oddly in the middle of the second half of the programme, rather breaking the plainchant spell. In general, the second half was more varied, with the Vetus abit littera somewhat quicker in tempo and Vache Sharafyan’s Lord who made the spring run providing a distinct feeling of being washed by waves of sound.

For an encore, we were treated to a light-hearted piece: Romeo and Juliet by Peter Erskine, a stablemate of the Hilliard at their recording company ECM, and best known as a marvellous jazz drummer (and known to contemporary opera fans for his key part in Turnage’s Anna Nicole).

This is the first time I’ve seen the Hilliard, and it’s been an eye-opener: they sing music from over eight centuries and make it sound as part of a continuous whole in a way that I would not have believed possible. It will almost certainly be the last time, since they are disbanding towards the end of this year. I’m glad not to have missed them.