"Four oboes, which one is out of tune?": a lemur turned an ear-training app into a TikTok series

Sine is an ear-training app. It launched on iOS in Sep 18 and reached Android in October. Its features are about the same as those of an older ear-training tool from ten years ago. It took off because the app has a mini-game called "which one in the band is out of tune," and cutting that straight into short video made a 15-second listening quiz. Its own TikTok account hit about 30M views in one month and grew a fandom. Below: how it started, where the money comes from, who's copying it, and whether this playbook works for anything else.

A 2.33M-view oboe video

In Oct 9, the TikTok account @learn.sine posted a video titled "OBOE EDITION!" Four cartoon ring-tailed lemurs stand in a row playing oboes, and one of them is out of tune. Viewers have to guess which one before the answer is revealed. There are two rounds, and the caption asks people to post their scores in the comments.

The video got 2.33M views and 114k likes. The top comment was "they're all out of tune because they're oboes 🤬" with 24k likes, and second was "the first one was embarrassingly obvious." Scrolling down is a long stream of scores: "2/2, I'm in choir, never been in a band", "2/2 I play percussion", "0/2" (scraped via TikHub, 11-06).

The same day, the account also posted the big-instrument version (900k), a tuba version (400k), and "band camp" (320k). Three days earlier it had been posting questions like "what chord is this?" that mostly got a few thousand views.

What it is

On the store it's called "Sine: Ear Training Games," developed by MAOI LLC. On iOS it's credited to an individual, Ethan Liao. The teacher is a ring-tailed lemur named Sine. The content includes short music theory lessons, pitch / interval / chord recognition, perfect pitch training, and a few mini-games: Out of Tune, Rivals (a league), and Bifrost Run.

Pricing is restrained: no ads. The free tier includes the first unit, all instruments, and friend groups; games can be played 4 times every 6 hours. The Encore subscription is $1.99/month or $14.99/year after a 7-day trial, or a $29.99 one-time purchase (official site learnsine.com). Common competitors are priced around $40 to 80 a year.

Through Nov 6:

Neither store has charted on Top Grossing, so revenue isn't visible from outside.

Why this format took off

From Sep 10 to Oct 4, the account posted typical "theory questions": is this F sharp or F flat, what chord is this, which C is in tune. Of the twenty-some videos, only two passed 100k views.

In Oct 6 it changed the format: a row of identical lemurs holding the same instrument, one out of tune, find it. The trombone version got 170k, the next day trumpet 340k and orchestra 690k, then marching band 450k on day three, and then the 2.33M oboe video the day after. Over the following month most videos landed between 150k and 1.1M (10-20 violin tuning 1.12M, 10-21 trumpet 900k). Of the 103 videos' total views, over 90% came from the more than eighty posted after Oct 6.

The format works for a few reasons:

• A 15-second question anyone can answer. No music theory needed, just hearing which one is off. People in choir, percussion, or who play nothing all post their scores in the comments. The score-posting itself drives comment counts.
• Infinite reskins. Swap the instrument and you get an episode: clarinet, bassoon, bagpipes, marimba. Swap the setting: subway, cathedral, beer festival, pirate ship, dragon's lair. The comments keep ordering new ones ("what's next, play the tuba"), and the account follows and thanks the people who ordered in the captions.
• Very precise audience. The tags are #bandkids and #marchingband, which hit American middle and high school students who play in bands. This group is already active on TikTok, and they're the easiest to hook with the joke "your section has someone who's flat."
• The video is the app. The game in the video is the app's Out of Tune, so after watching you can immediately play the same thing.

After Oct 22, it added storyline: the out-of-tune character C is kicked out of the band, locked in a dungeon, and breaks out with another lemur named Nocturne, with a queen in pursuit and the clown Bobo showing up now and then. The challenge account slowly turned into a serial. "Is C still alive?" became a comment-section topic.

Where users come from

Nearly all of it comes from the account's own short videos, mainly on TikTok. The same videos also go to YouTube Shorts and Instagram (@eartraining.games). The App Store reviews are blunt:

"I came from the flood of TikTok ads. I wasn't expecting much, but I love those little videos." (10-17) "My Insta feed was flooded with Sine's funny ads, and then I got hooked." (10-26) "I came from its Shorts on YouTube." (10-24)

The "ads" users mention are most likely these organic videos: none of the TikTok posts I pulled are labeled as ads. Whether they paid to boost them isn't visible from outside (unverified).

Two more channels:

• The fandom. Searching #learnsine on TikTok turns up lots of fan edits. The most-liked one is "justice for C chat #nichefandom," with 210k views. There are dedicated fan accounts and an officially verified Discord. On Reddit someone asked whether the art style was AI-generated.
• iOS first, Android second. In Oct 4 the Android version launched, and TikTok posted "We are now on ANDROID!!" Two days later the format exploded, and Android caught that wave, bringing in about 26k installs in a month.

No media coverage, and almost nobody on X has mentioned it. The founder posts "dev logs" on TikTok explaining why the paywall changed (11-01), and replies to App Store reviews one by one, promising to make the interval and chord exercises free.

Will users stick, and where does the money come from

The iOS reviews split clearly. Praise centers on "no ads," "not pushy about subscriptions," "cheap," and "the mascot is adorable." Some music students say they battle classmates on it in the school building, and a teacher says they'll use it with students. The deductions are almost all about the paywall: "the game only lets you play 4 times," "the most important interval training is locked behind the subscription," and one two-star review is titled "subscription junk."

This shows one thing clearly: the main users coming from videos are teens. They love to play, but they don't necessarily pay. Android rating count is about 2% of installs, with decent activity, but it hasn't charted on Top Grossing on either platform, so paying rate and revenue are blank. The official site says players have collectively identified over 200 million notes.

Growth is also cooling. On Play, from 10-30 to 11-04 the average daily new installs were about 1,300; by 11-05 and 11-06 it was down to around nine hundred. Per-video TikTok views fell from 500k–1M in mid-October to 200k–450k in November. In Nov 5 it teased a new rhythm game about "who jumped the beat," apparently looking for the format's next season.

Who it's competing with

Ear training is an old category, and this year several new "perfect pitch" products have joined. Sine's features aren't special, and its installs aren't the biggest either:

The one to watch is Pitch Master. Its handle @learnperfectpitch uses an almost identical format: 5,579 followers, 45 videos, single videos at 3K to 20K views, two orders of magnitude behind Sine. Copying the format is easy. The hard part is the characters, the storylines, posting 2 to 5 times a day consistently, and the comment section Sine has built up.

If it were you

B: Worth learning from this playbook, but don't copy the ear training. You could take the "App gameplay = 15-second challenge videos + lovable characters that can run as a series" move and apply it to a skill nobody has tried this way yet. Revenue hasn't been proven, so you're betting on it.

Who it suits: 1 to 2 people, one of whom can cut 2 to 5 short videos a day and can draw, or consistently generate the same characters. Ideally you're already inside the target community (playing in bands, learning languages, gaming, practicing art), so you know which jokes will land with these people.

Who it doesn't suit: anyone trying to head-on build a "better ear training app" (features are saturated, Sine has a fandom, and Pitch Master already copied the format); anyone who only wants to write code and won't create content every day (nine-tenths of this business is video work); anyone who needs to see revenue quickly (teen users play more than they pay, and Sine itself has never reached the Top Grossing chart).

How to do it: Find a skill that can be answered by "listen once / glance once," such as rhythm and beat-catching (which Sine itself only just started), foreign-language pronunciation discrimination, color difference recognition, or harmony. Or switch the audience, to choral groups, guitarists, or K-pop trainees. Build the core game first as 3-choose-1 questions: same visuals, change one variable, and you have a new episode. Make the free tier generous, bring subscriptions down to around $15 a year, and no ads.

How to get users: Start with TikTok only, and cross-post to Shorts and Reels. In the first two weeks, try several question formats. Whichever one gets a single video past 100K becomes a daily series. Every caption should get viewers to post their scores in the comments and tap for the next episode. Once you have a steady audience, add character storylines. Don't rush onto Android in the first month. Once a video takes off, expand platforms while the momentum is there.

Deadline: US school bands and choirs peak in the fall/winter semester and the year-end performance season. (Inference) Ideally start daily posting before mid-December, and have the first video pass 100K views before January.

Signs you misjudged it: ① After 30+ videos and three different formats, not a single one passes 50K views, meaning this skill can't carry this format; ② Sine's public revenue or rankings show it has never made real money (for example, it still hasn't charted on any top list by next Q1), meaning teen traffic won't convert; ③ Copycat accounts like Pitch Master reach hundreds of thousands of views per video within weeks, meaning the format bar is lower than you thought and the window is closing.