Matthias sings the mantra "Ad Gurenamay" on a Saturday evening Satsang at Yoga Vidya in Bad Meinberg. You can find this song under no. 552 in the Yoga Vidya Kirtan booklet.
Further explanations of this Kirtan can be found online in the Yoga Vidya Kirtanheft Blog at Ad Gurenamay.
Here is the complete text to sing along:
Siri Guru Devay Namay
If you are interested in seminars with music, you can find here seminars on mantra and music. For more kirtan and Mantra vocal recordings click here. For more information on Yoga, meditation and Ayurveda can be found on the internet pages of Yoga Vidya.