Everyday Life of a Top Student at Hogwarts

Chapter 323 Sonar Improvement and Frequency Analysis

The Black Lake was cold and still, save for the slow, rhythmic movements of Karen as he paddled, and the steady beating of his own heart and breathing echoing within the bubbles formed by the Bubble Head Charm. He hovered in the deep water not far from the shore beneath the Ravenclaw Tower, surrounded by a hazy darkness, with only a few scattered aquatic plants emitting a faint bioluminescence.

He closed his eyes, trying to clear his mind and concentrate his mental energy. Magic flowed slowly through his body, not to cast a specific spell, but to resonate in an extremely subtle way in his throat, chest, and even the tip of his wand, emitting a specific low-frequency fluctuation that was almost imperceptible to the human ear but clearly discernible on the magical level.

He had been practicing this for several weeks. At first, it was just a vague feeling, but now it was gradually becoming clearer. As the invisible sound waves spread outward from him to the surrounding waters, the objects they touched reflected extremely subtle fluctuations, which were captured by his "Eye of Truth" and his magical perception, which had become exceptionally sharp after being trained at a special frequency.

Within his perceived "field of vision," the surroundings were no longer absolute darkness. He could "see" a clump of dense, irregularly shaped aquatic plants swaying gently with the current about fifty feet to his left; a pile of jagged rocks to his lower right, their outlines rough and solid; and directly ahead, several slender fish with faint magical auras were lined up, nimbly darting through a crevice in the rocks. He could even vaguely sense further away, several blurry orbs of light representing Grindelwald, carrying a hint of malice and restlessness, swimming in a depression, but they seemed unaware of his presence.

This "sonar perception" ability is far more effective underwater than in air. Water, as a medium, transmits these magical fluctuations more effectively and makes the feedback clearer. However, limitations remain apparent. He can sense the outlines, approximate sizes, and movements of objects, but cannot discern details—such as the specific species of the seaweed, the color of the scales on the small fish, or Grindelwald's ferocious appearance. The perception of emotions is also more vague, limited to very strong tones, such as calm, curiosity, hunger, or anger.

Maintaining this perception also consumed a significant amount of mental energy. Less than a thousand minutes later, Karen felt a throbbing pain in his temples, and a sense of mental exhaustion washed over him. He slowly stopped outputting magic, and the strange "vision" disappeared. The surroundings returned to a state dominated by the magical vision of the "Eye of Truth"—he could see the flow of magic, but the outlines of non-magical entities were far less three-dimensional than sonar perception.

He swung his legs and floated to the surface of the water.

"How was it? Any improvement this time?" Wesley asked impatiently as he climbed onto the lake shore and dried his hair with a towel. He, Fabian, and Ernesto were responsible for guarding the shore tonight, although Karen was only practicing in a relatively safe area near the shore.

"The range has expanded a bit, extending to about sixty feet, and the outlines are clearer," Karen replied, her voice tinged with weariness, as she changed out of her soaking wet vest and into a dry robe. "But the old problem persists: details are unclear, and the duration is still insufficient. Furthermore, the emotional response remains vague; I can only sense a general 'good' or 'bad'."

"That's already quite remarkable, Karen," Fabian said earnestly, adjusting his glasses. "It's like you have an extra pair of eyes, eyes that can see through darkness and obstacles. It's more than enough to warn of and avoid danger."

“Fabian is right,” Ernesto leaned against a rock, gazing at the calm lake. “You’ve figured out quite a bit about the mermaids’ patrol routes, the distribution of Grindelho’s lairs, and their outpost locations, haven’t you? It’ll be much easier for us to collect dark algae next time.”

Karen nodded; he knew his roommates were telling the truth. This unexpected ability was incredibly useful, but he also had another, more complex and frustrating matter weighing on his mind.

Back in their warm, bright dormitory, it was already late at night. Wesley yawned, climbed into bed, and quickly fell asleep. Fabian was still under the lamp, organizing charts and records about the relationship between the activity of dark algae magic and light intensity. Ernesto, meanwhile, was calculating the exact time of the next peak of astral magic; the closer the time, the more accurate the calculation.

Karen didn't rest. He walked to the central open space and focused his mind again. But this time, his practice was no longer about wide-range sonar perception. Instead, he tried to concentrate his magic at his fingertips to simulate extremely complex and ever-changing combinations of frequencies.

These combinations stemmed from his in-depth research into Slytherin sonic technology data, combined with the previously recorded magical fluctuations of Harry Parseltongue, and supplemented by the "Eye of Truth's" insight into the magical rhythm emanating from the flashing Authority Lock runes on the rock wall.

At his fingertips, wisps of light flickered and vibrated at different rhythms, emitting subtle hums that only those with an extremely keen sense of magic could detect. He experimented with hundreds of combinations, from simple frequency stacking to glissando mimicking the hiss of snakes, and even incorporating different magical attributes, such as coldness, corrosiveness, and commanding will.

However, each attempt was like throwing a stone into the sea. After yet another failed attempt at combining complex frequencies, Karen let out a soft sigh, fine beads of sweat appearing on his forehead. He walked to the table and picked up the replica of the access lock that Nico had copied based on the information Karen had provided. Although Nico himself wasn't sure if it was the same as the original, the lack of response still gave Karen a small blow.

"Still not working?" Fabian looked up and asked with concern.

Karen shook her head, her brow furrowing slightly. "Absolutely no response. I even tried superimposing and mutating Harry's Parseltongue vocalizations with the flashing frequency of the runes when the portal opened, but it all failed. This thing—is far more complex than we thought. It might require more than just the correct 'sound' or 'frequency'; it could very well incorporate the unique bloodline imprint of the Slytherin themselves, or some kind of 'key' that we can't understand, containing a specific will and magical code. Of course, we'll have to wait until we go underwater and test the original to find out."

Ernesto stopped calculating and turned around: "So, the chances of cracking it through simulation alone are slim?"

"At least with our current capabilities and time, yes." Karen placed the log back on the table, her tone certain. "It's too intricate, like a lock that requires several keys to be inserted simultaneously, along with a specific combination. If any link is missing, or the order is wrong, it won't open."

"So—that's the only option left?" Fabian lowered his voice.

Karen nodded. "Yes, Harry. He's the most likely living key we can find to trigger this access lock. It's risky, but it seems to be the only viable option in the short term."

The following evening, Karen contacted Nicolas Flamel and Castor through a two-way mirror. On the crystal mirror, Nicolas's image was clear, while Castor seemed to be sitting in the shadows a little further away, only a blurry outline visible.

"Master, regarding the Slytherin access lock—" Cullen gave a detailed report on his progress with sonar perception and his numerous failed attempts to crack the access lock, "—I tried almost every frequency and magical combination I could think of, including data combining Harry's Parseltongue characteristics and the Entry Rune, but all failed. I think the possibility of directly simulating a crack is extremely low. It likely requires a direct authentication at the bloodline or soul level."

On the other side of the mirror, Nico stroked his long white beard and nodded slowly: "Your judgment is likely correct, Karen."

Salazar Slytherin was known for his caution and obsession with his bloodline. He would never allow his core knowledge to be easily stolen or imitated. "You did well, making timely judgments and not blindly wasting energy on a seemingly dead-end path."

Castor spoke from the shadows, his voice as deep and calm as ever: "So, the backup plan? That boy?"

"Yes, Professor," Cullen admitted. "I think Harry Potter is the most likely key right now. But how and when to use it requires very careful planning and safeguards. But first and foremost, we need to get the item out of there."

"Of course," Nico's voice turned serious. "Unless we are fully prepared, we must not allow Harry Potter to access those things lightly. We don't know if the access lock might be hiding something else, or if it contains any dangerous traps or magic. Your primary task right now is still to thoroughly study the data we have obtained, ensuring that we can conduct more efficient exploration and recording next time we enter the laboratory. As for the access lock—put it aside for now. If it is ultimately confirmed that it cannot be opened safely, our previously agreed-upon plan of taking it away remains the final option."

"I understand," Karen replied. "We'll prioritize safety."

"Ernesto," Castor's voice turned to Ernesto, who was checking astronomical data, "the next window?"

Ernesto immediately picked up a piece of parchment filled with data and brought it close to the mirror: "Callen and I have calculated and confirmed, Professor. The next most suitable window for peak astrological magic is in mid-May, specifically between May 15th and May 18th. Among them, the peak probability is highest on the night of May 16th and the early morning of May 18th, and the energy intensity is also expected to be stronger than that in February."

"Very good," Castor replied briefly. "I will come again then. Until then, Karen, continue your underwater training, especially your new sensory abilities. They will be very helpful for underwater exploration."

"Yes, Professor."

After the communication ended, Karen felt the pressure on her shoulders ease slightly. The mentors' approval and clear instructions freed her from worrying about the unbreakable access lock, allowing her to focus her energy on more targeted matters.

In the days that followed, Karen dived into the Black Lake even more diligently, practicing his sonar perception. He gradually expanded his exploration area, avoiding the mermaid's core territory and known danger zones, and created more detailed underwater topographic maps and biological distribution maps. He even tried using this perception to track the movement of some small schools of fish, testing its accuracy and endurance.

With each dive, each extension of his senses, he gained a more refined control over his ability and a deeper understanding of the deep, icy Black Lake. He made as many preparations as possible for his second exploration, both anticipating the arrival of May and maintaining the necessary awe and caution towards the secrets of Salazar Slytherin hidden deep beneath the lake.