At one time, for a significant portion of Twilight Sparkle's life, friendship had been very low on her list of priorities. Even once she had discovered friendship's value and importance, she had been content to let herself be carried away by its flow than be proactive or analyze it at any great length. Simply sticking with the five ponies that had helped her to overcome Nightmare Moon, who shared the responsibility of being bearers of the Elements of Harmony, had come naturally.
Then she had become the Princess of Friendship. Aside from that sparking the need to prove that there was substance to her title initially, which led to her reaching out to Yakyakistan, as well as her "friends" in Canterlot despite never caring enough to even remember their names, after more experience she started a school where anyone could learn about friendship: because some didn't see the value of it, thought it wasn't worth the investment, or actually found it to be a foreign concept.
Sometimes, however, even when the benefits of friendship was experienced by someone, the positive emotional impact was minimal or nonexistent, leading to no real desire to incorporate it into their lives — unless it was used to manipulate someone. That had inspired her to go further and find a way for others to know what friendship felt like at an advanced level, in the way that she and many others did, so they would know what they were missing and make a better-informed judgement.
After much study and many experiments, she found a delivery system that worked well with her personal strength, magic, and was receptive to most beings: music. Once she was sure that her "friendship music" — term pending further consideration — would work on sapient beings as well as sentient, she quickly got one of the many empty rooms in her castle ready for testing it on ponies.
That brought her to the present, as one of the two test subjects in the aforementioned room. Originally she hadn't planned on being one of the test subjects, but working with DJ PON-3, the only pony in Ponyville who could help her produce and record her friendship music, had piqued her interest. She knew her by her stage name and reputation, and had encountered her plenty of times in the past, yet she didn't know her real name and couldn't even put a voice to the pony. In fact, despite all of the time that they had spent together as of late, she had somehow avoided speaking at all.
Thankfully, DJ PON-3 had agreed to join her as a test subject, although she was pretty sure that the other mare hadn't fully grasped what her friendship music did. She felt that it was a little underhanded to not remedy that, but she couldn't pass up the opportunity to open up a line of communication, so she could get an opportunity to learn more about the enigmatic pony that she had worked with, who happened to live within the shadow of her home.
Turning her head away from the music player that she was about to switch on, she regarded the mare in question, who was patiently sitting on one of the two cushions in the middle of the room. In her periphery she noticed the only other addition to the room: a folding table bearing beverages and snacks. "Are you ready?"
After receiving the expected non-verbal response, which came in the form of a single nod, she mentally grinned and pressed play.
As soon as the dubstep song reached her ears, she stiffened when the magic of friendship hit her with a greater effect than she had anticipated. Typically friendship was built over time by specific experiences, which defined the nature of the friendship and gave it a unique quality, but without those filters her feelings toward DJ PON-3, regarding all of the elements of friendship, were dialed up all the way for everything.
Intellectually, she knew that there was a possibility of it being a problem, in part because it certainly didn't feel like one right then, but she couldn't figure out how it was a problem or how it could become one. However, with the resolution only an off-switch away and accessible from anywhere in the room, should it be needed, she felt confident enough to continue with the experiment as-is.
So, she turned the rest of her body away from the music player and approached DJ PON-3 as she asked, "Are you feeling comfortable enough to proceed?"
She was disappointed to see her answer with a nod, even though she had expected a non-verbal reply. Once she was settled on the cushion across from her, she felt no reservation in asking, "How come you don't speak?"
"I'm embarrassed by the sound of my voice," DJ PON-3 readily answered, who sounded more like a filly affecting cuteness than a cool mare.
The sound of her voice was such a surprise that it took a moment for Twilight Sparkle to recover enough to respond. "It was certainly unexpected," Twilight Sparkle admitted, before she encouragingly added, "but it doesn't sound bad! It just makes you more unique!"
"Maybe," DJ PON-3 hedged. "That doesn't change the fact that it's at odds with my lifestyle and career, though."
Twilight Sparkle furrowed her brow in thought, as she tried to solve the problem being presented to her like she would have as a student in school aiming for a perfect score, with a drive seldom seen when it didn't involve someone important to her. Eventually, she brightened when an idea occurred to her, at which point she exclaimed, "I have it!" She enthusiastically thrust a hoof at DJ PON-3. "You can produce songs under a pseudonym and find out how your voice is received!"
DJ PON-3 was silent for a moment, with her head bowed in contemplation, before raising her head and reservedly saying, "I guess I could..."
"It's better to know the truth and work from there," Twilight Sparkle began to lecture, from a place of personal experience, "than make an assumption out of fear and potentially miss out on something more desirable."
"Also," she casually continued, "unless you already have a place where you feel secure enough to use your voice, feel free to come here and give it some exercise — I won't mind."
DJ PON-3 waved the idea away with a hoof. "You're just saying that because of the music."
Twilight Sparkle's horn lit up and the room went quiet after a click sounded from the music player. After mentally adjusting from the sudden loss of the strong feelings being engendered by the music, she straightened up and adopted a solemn expression on her face before earnestly saying, "I'm serious. I have more space than I know what to do with, and I'd be happy to chat with you if you're interested."
Habit made it difficult for DJ PON-3 to speak despite having spoken already, but that gave her plenty of time to think before she finally asked, "Are you sure? I mean," she struggled a bit to find the right words, "we're so different, you know?"
"So?" Twilight Sparkle replied, with an eyebrow cocked. "I have little in common with most of my friends. And as for me being a princess?" She shrugged. "There have been some issues, but nothing that couldn't be worked out."
In response, DJ PON-3 used her magic to raise her sunglasses to the base of her horn, then offered a hoof as she grinned and said, "I'm Vinyl Scratch. You should at least know that if we're going to be friends."
Twilight Sparkle smiled and happily shook hooves with her new friend.
"So," Vinyl Scratch went on, as she lowered her sunglasses back into place, "what all did ya want to do with this experiment? Just sit and talk?"
Rubbing the back of her head, Twilight Sparkle sheepishly replied, "Did you have anything else in mind, that you'd like to do?"
Her reservations now fully shed, Vinyl Scratch got to her hooves and turned the music back on as she declared, "Let's dance!"
Not needing the music's magical influence to be receptive to the idea, Twilight Sparkle hopped to her hooves and joined Vinyl Scratch on what was now the dance floor.
Their different backgrounds and lifestyles were quickly highlighted by their dancing, but Twilight Sparkle couldn't feel embarrassed by her performance thanks to the music, since she would normally have nothing to worry about among friends. Vinyl Scratch, upon seeing the moves of a life-long bookworm and homebody, decided to show and teach her some new ones, to the extent that they suited the music.
Time passed without notice for them while the magic-backed music played, as they danced, took the occasional break for snacks and refreshments, and chatted throughout. As a result, they forged a bond that was comparable to the one that formed between Twilight Sparkle and the other Elements of Harmony after their ordeal with Nightmare Moon. By the time the experiment came to an end, they knew — without a doubt — that they would be finding the time to see each other again before long.
After the experiment was officially over, they shared a casual parting hug while standing within the open doorway of the castle's entrance before Twilight Sparkle warmly said, "See you tomorrow."
"Sure thing, Twilight," Vinyl Scratch quietly replied, to avoid anyone else hearing her voice. "I didn't know what to expect when I decided to be a part of your experiment, but it was totally worth it." Then she appeared to remember something. "Oh, I'll take your advice and start speaking with Octavia in the privacy of our home — I'm sure she'll dig it."
Twilight Sparkle smiled at that, since Vinyl Scratch had restricted her speech for all but a few occasions, so she'd be in the habit of remaining silent in public. Her foalhood friend, Octavia Melody, definitely hadn't been a fan of that policy, so Twilight Sparkle had recommended making one more exception, confident that the DJ had enough experience to keep herself from accidentally speaking in public.
With a final goodbye, Twilight Sparkle watched her new friend walk away, already looking forward to their next meeting. Like many of her other friends, connecting with someone really different from herself proved to be both interesting and fun. The music had made the experience even more unique, because it felt like she'd connected with Vinyl Scratch to the extent that they'd been friends for a long time, rather than the few hours that was the reality.
That aside, she was happy with the outcome of the experiment, even though the magic would need to be tweaked, so as to not have such a strong effect. She figured that it might be overwhelming for those that weren't familiar with friendship.
She idly wondered if she should contact her sister-in-law and experiment with imbuing music with love next, and chuckled at the thought that that idea had inspired. Vinyl Scratch had jokingly called the combination of her music and the magic of friendship "budstep", so she had imagined that her new friend would have called Cadence's version "wubstep."
It was something to consider.
Author's Note
As my mind is wont to do, it decided to flip around "dub" in "dubstep" out of the blue, and stuff just snowballed from there. And I went with it. 
