Which tone to hum for soulcasting?

[+Oltux72 he/him]

First of, it was all there from the very start. Shallan got a book that recommended humming to aid in soulcasting. After Rhythm of War it is clear why humming would work.

But that leaves out which frequency you should hum at. Honor's tone or Cultivation's tone? And should you use a rhythm? Do essences have rhythms?

[RoyalBeeMage he/him]

i think it would be the rythem of the tower as it would combine both honer and cultivation like in towerlight.

[alder24]

4 hours ago, Oltux72 said:

First of, it was all there from the very start. Shallan got a book that recommended humming to aid in soulcasting. After Rhythm of War it is clear why humming would work.

But that leaves out which frequency you should hum at. Honor's tone or Cultivation's tone? And should you use a rhythm? Do essences have rhythms?

I've found those references of humming during Soulcasting, WoK ch 5:

Quote

Jasnah closed her eyes, pressing her hand against the fallen boulder. She raised her head, inhaling slowly. The stones on the back of her hand began to glow more fiercely, the smokestone in particular growing so bright it was dificult to look at.
Shallan held her breath. The only thing she dared do was blink, committing the scene to memory. For a long, extended moment, nothing happened.
And then, briefly, Shallan heard a sound. A low thrumming, like a distant group of voices, humming together a single, pure note.
Jasnah’s hand sank into the rock.
The stone vanished.

This doesn't look like Jasnah was humming, rather the stone itself was humming a pure tone.

The quote you've mentioned, WoK ch 42:

Quote

However, she’d found a book the day before that had offered what seemed like a useful tip. It claimed that humming, of all things, could make a Soulcasting more effective. It was just a passing reference, but it was more than she’d found anywhere else. She sat down on her bed and forced herself to concentrate. She closed her eyes, holding the stick, imagining it transforming into quartz. Then she began humming.
Nothing happened. She kept on humming though, trying dierent notes, concentrating as hard as she could. She kept her attention on the task for a good half hour, but eventually her mind began to wander.

When Venli tried to Stoneshape for the first time it was the stone that hummed the rhythm, not her, and this voice was similar to the one described by Shallan in the first quote. The stone also noticed the tone of Voidlight. I think the tone was the pure tone of Cultivation, but this is just a guess. RoW ch 67:

Quote

The stones trembled. They spoke with one voice, but she felt as if it was also many voices overlapping. Not the voice of the tower, but the voices of the many different sections of stones around her. The walls, the ceiling, the floor.
Radiant, the stones said. We have … missed your touch, Radiant. But what is this? What is that sound, that tone?
“Voidlight,” Venli admitted.
That sound is familiar, the stones said. A child of the ancient ones. Our friend, you have returned to sing our song again?
“What song?” Venli asked.
The stone near her hand began to undulate, like ripples on the surface of a pond. A tone surged through her, then it began to pulse with the song of a rhythm she’d never heard, but somehow always known. A profound, sonorous rhythm, ancient as the core of Roshar.
The entire wall followed suit, then the ceiling and the floor, surrounding her with a beautiful rhythm set to a pure tone. Timbre, with glee, joined in— and so Venli’s body aligned with the rhythm, and she felt it humming through her, vibrating her from carapace to bones.

Later Venli attuned herself to the mixed tone of Cultivation and Odium when Stoneshaping - Odium's tone because she was using Voidlight, Cultivation's tone because Venli belongs to Cultivation. RoW ch 83:

Quote

It felt wrong to be using his Light to practice her Surgebinding, but the stones whispered that it was well. Odium and his tone had become part of Roshar, as Cultivation and Honor—who had not been created alongside the planet—had become part of it. His power was natural, and no more wrong or right than any other part of nature.
Venli searched for something else. The tone of Cultivation. Odium’s song could suffuse her, fueling her powers and enflaming her emotions, but that tone … that tone had belonged to her people long before he’d arrived. While she searched for it, she listened to her mother’s songs in her mind. Like chains, spiked into the stone so they’d remain strong during storms, they reached backward through time. Through generations.
To her people, leaving the battlefield. Walking away rather than continuing to squabble over the same ground over and over. They hadn’t merely rejected the singer gods, they’d rejected the conflict. Holding to family, singing to Love despite their dull forms, they’d left the war and gone a new way
The tone snapped into her mind, Cultivation and Odium mixing into a harmony, and it thrummed through Venli. She opened her eyes as power spread from her through the stones. They began to shake and vibrate to the sound of her rhythm, liquid, forming peaks and valleys in time with the music. The floor, ceiling, and walls before her rippled, and a trail of people formed from the stone. Moving, alive again, as they strode away from pain, and war, and killing. [...]
The power slipped from her, as it always did. The tone faded, and her control over the stone ended. She needed more practice and more Light

 

I don't know which tone the book is talking about. It might be just pure tone of Honor, because they are using Stormlight and they are humans, belonging to Honor (for the same reason Venli tried to attune herself to the tone of Cultivation - she belongs to Cultivation, humans belong to Honor). It might be the pure tone of Cultivation (or pure tone of Roshar itself), because the object, rock for example, belongs to Roshar and that's what the rock is humming and a Radiant needs to attune themselves to this tone. Or it might be a combination of both Honor and Cultivation's tone because they're using Stormlight on the object belonging to Roshar.

I think Honor's pure tone is the most likely to be the answer given Venli's example of Stoneshaping and reasons why she was humming a mixed tone of Odium and Cultivation.

[Duxredux he/him]

Thinking out loud, it may not be a pure tone of Roshar. Allomantic pulse patterns dictate what Allomantic metal is being burned to the senses of a Seeker, and despite all Allomantic abilities being powered by Preservation they do not have the same pattern. For the same reason, I'd assume that despite all the Radiant abilities except a couple weird outliers being powered by Stormlight, each ability would have a different tone/rhythm if listened to by a Seeker. On the other hand, a skilled Seeker can even identify what emotions are being manipulated by a Soother, so not sure how that really works. I could see Soulcasting either making tones on a similar spectrum as the Metallic Arts, or possibly to the same degree of variation that a Soother emits when targeting different emotions. 

So... my answer is the tone to hum is probably whatever a Seeker would hear or whatever Shallan heard, which may or may not be a pure tone. alder24 has good stuff though.