MaColl was too much of an actor for me when it came to singing Folk Songs, and there is no Scots accent the way he used to sing it, however he was a belting teacher of vocal production, and in the 'Song Carrier Programmes' (Home Service 1960's!!!!) Introduced me to the use of vibrato, the shake decoration and use of portamento.
He then broke every rule in the book on his histrionic performance of the Brake of Briars on the Manchester Angel recording. That said he did address the matter of pitch, but never expanded upon it. He used the 'Gathering of the Clans' as his 'warm up song' on a gig. I just howl like a lunatic in the car in an attempt to get my voice going, and try not to write off the car and a lamp post on the way to a gig.
Martyn Wyndham Read is the best modern singer I have ever heard. He very rarely uses any decoration or much vibrato. I got a lot of advice about maintaining tone from him. His pitch is perfect lucky bugger.