This is a subject I am definitely not an expert on, but something that is somewhat dear to my heart. Galdr is a form of verbal or chanted spell. From what I understand, there is no real specific knowledge on what form Galdr took precisely, but I have encountered a few versions that I'd like to talk about.
One of the simplest explanations I've heard of Galdr is that it is 'singing the runes'. I've seen this singing taken in two very different directions. Either the name of the rune itself can be sung or the sound associated with the rune can be sung. The examples I have heard of this is very melodic, definitely more aligned with singing than with a monotonic chant or spoken word.
Another completely different take on Galdr is a sort of spoken charm, linked to both the name and sound of the rune. The example that sticks out most in my mind is the 'fe fi fo fum' that most of us know from the Jack and the Beanstalk fairy tale. Some people consider this to be a Galdr for Fehu. That theme, of chanting the base sound with different interpretations (often using the different vowels) can be used to Galdr any of the runes.
I've tried these different methods of Galdr, and had varying amounts of personal resonance with them. Some runes I Galdr quite well by singing their names. Others I feel quite strongly when I intone their sound. The 'fe fi fo fum' method hearkens me back to my childhood and definitely has a strong sense of play to it.
What I find about all of these is that they remind me of other vocal methods of toning. Many paths use spoken word or sounds as a form of sacred practice. From my very first days, I don't speak in my normal voice when I cast or do ritual. My voice either drops and gets deeper or softens and gets lighter. To me, taking my own voice out of it's normal pitch in this way is a way of honoring the sacredness of the moment.
I've done some work with the Ceremonial method of intoning sacred names. For me, this feels like I am speaking from a place that is bigger than me, like I am opening up and letting the words speak through me. While not really uncomfortable, it never felt like me.
I was introduced to chanting years ago now, by the local Pagans I work with. It is something that has definitely become a huge part of my own practice, and something that I absolutely love. We also enjoy singing for pleasure, and working on other vocal related things. Many of the chants I love are more song-like than simple chants (although I do love some very simple chants as well). I have always found it interesting that chanting doesn't feel the same as singing, even when the chant is probably a song (aka: when it is many verses and little or no repeated lines). Of course, I have been exposed to call style chants (like the Hawaiian ones) which are often non-repetitive. But though many lyrical songs move me and bring emotions to me (and have been used in my practice because of the emotions they call in me), I still feel different chanting. Chanting can bring me out of myself.
One of the things I love about voice based work is that it is always there with me. There is power in sound, and we can harness it almost without thought. But I also feel that power words have resonance even when unsounded. There are times that I 'speak' my words inside my own head. They still have a voice, in fact my mind has many different voices. The words I speak inside have a different energy than the ones I speak out loud, but they do have an energy.
Perhaps I haven't found my own Galdr voice yet. But I tend to think about Galdr as a way of thinking about voice based working rather than a particular type of voice based work. Just as there are many styles of music, perhaps there are also styles of Galdr. When we open our mouths and create magic with our voice, I feel that is Galdr. It can be whispered or shouted, sung or chanted, spoken or laughed. It can be our way of speaking our truth to the world, or how the world speaks truth to us. We can be the voice or we can open ourselves to the voice. We each have a unique voice, and our words can quite literally change the world. We just have to let ourselves speak.