I just read a bit about Carl Hardebeck. He was raised in England, with a German father and Welsh mother, but worked in Belfast as an adult and learned Irish.

some excerpts from History Ireland magazine.

1) When Carl was nineteen and still at school his father invested what at the time was a small fortune to provide for his future security; at the same time advising his blind son to make himself independent by developing his talents. Before he was twenty-three he had won diplomas as organist and pianist, still a pupil of Frederick Corder. Though also fully qualified as a teacher of music he doubted he could earn his living as a tutor. Deciding to use some of his investments to open a music store, he left London for Belfast. With a partner to run the business side of the enterprise he established himself in the northern capital. The venture failed when the money allowed by his trustees ran out, and his partner disappeared.

‘Professor of Music’

The disillusioned young man decided to remain in Belfast. Now twenty-seven, he reluctantly erected a brass plate at his residence in Limestone road: ‘Carl Gilbert von Hardebeck, Professor of Music’. He was invited to take on the job of organist and choirmaster in the church of the Holy Family, then a poor corrugated iron chapel in Newington Avenue. He later moved to St Peter’s pro-cathedral on the Falls Road where his devoted choirboys called him ‘Tantum Ergo’. For his part, demonstrating a sense of humour that stood him in good stead in his difficult life, he poked fun at the ‘holy growlers’ in the men’s confraternity, and the ‘chronic drouths’ of the Total Abstinence Society.

2) Learnt Irish

The collections of the pioneers, and the poetry of Ferguson, James Clarence Mangan and Standish O’Grady, and the Gaelic scholar, Dr George Sigerson who had recently published his anthology, Bards of the Gael and the Gall provided a rich resource for the study of the inheritance of Irish traditional music. With the same enthusiasm Hardebeck recruited Sean Ó Catháin and Tadhg Mac a’Bhaird, native speakers, to teach him Irish; accepting the task from the conviction that without some knowledge of the language the musician would not understand the principles of Gaelic poetry, ‘essential to the proper appreciation of the music to be noted’. Never having acquired fluency in speech, he mastered the phonetic principles and understood its poetry. The realisation that here was a culture of great antiquity excited him: ‘The Irish tonalities did not originate in the Greek or Latin…the Gaelic language and poetry are at least as old as Latin or Greek’.

is admiration for the Irish speaking ‘peasant of Donegal, Cork or Mayo’ knew no bounds; the humble cottier had ‘a far higher sense of true poetry than even the average university graduate’ and a ‘more natural refinement than three-quarters of the aristocracy’. ‘Their poems voiced the feelings of the people and their history’, he wrote in the preface to Part II of Gems of Melody: A Collection of Old Irish Melodies. ‘The melodies are so beautiful, that they alone—if every other proof were wanting—show that the people who produced them must have been a highly artistic, cultured and civilised nation.’
At the Feis Cheoil in 1900 he placed himself among the traditionalists with his cantata, The Red Hand of Ulster. His conversion to an Irish idiom was confirmed at a Gaelic League concert in the Ulster Hall on St Patrick’s Day when he heard Mairtín O’Conlon, from County Clare, perform unaccompanied songs in the singer’s native Irish. ‘I was so enchanted by the flow, the rhythm, the rise and fall of melody and, above all, the simplicity and character of this music that I decided to leave all and follow it.’

Braille board and stylus

In the Donegal Gaeltacht he visited the cottage homes of Cloughanelly, Glencolumcille, Gweedore and the Rosses, collecting songs; he ‘gathered them eagerly and studied them minutely’. O’Boyle recorded a graphic description of the pioneer song collector at work, before the invention of the Dictaphone. The ‘Fear Mór Dall’ coming in on the arm of his guide, stooping low through the small door, with a Gaelic salutation on his lips. Sitting in the chimney corner, he took out his Braille board, frame and stylus, and called on the ‘singer of the household’.
In Hardebeck’s own words, taking down a traditional air was no easy task, especially from a singer when asked to repeat a phrase, had to go back to the beginning of the music and the poetry. ‘This means you have to take him up when he comes round to the phrase you want. You have to write as fast as you can to keep up with even the slowest singing pace…If you can write the words below the notes, so much the better…Without the words you have only lost time, taking down a skeleton of the tune.’
He brought to his life’s work the insights of his training and experience in the accompaniment of plain chant, and discovered that Irish melodies were composed in the same modes. ‘I found that the study of plainsong which I pursued with my friend Arthur de Meulemeester…was the greatest help to me in learning to understand the scale and principle of modal music.’