Soundle asks you to guess the frequency of a pure tone. A random sine wave plays somewhere between 220 Hz and 1760 Hz, and you hunt for the same frequency with a slider. Absolute pitch is not required; knowing a couple of reference points is enough.
How it works
When the round starts you hear the target. You can replay the target up to three times, but you can listen to your own guess as often as you like. The strongest tactic is A/B comparison: hear the target once, move the slider somewhere, play your own tone, listen to the gap, close in.
The range spans three octaves and the slider is logarithmic. The same amount of slider movement covers the same musical interval anywhere on the scale; 20 Hz is a big step at the bottom and almost inaudible at the top.
Scoring
Your error is measured in cents, where 1200 cents equals one octave. How many cents you finish from the target decides your score, and after everyone submits you are ranked closest to furthest: first +3, second +2, third +1. Cents rather than raw Hz precisely because of that logarithmic scale: a 200 Hz miss is a disaster low down and a small nudge up top.
Reference frequencies
You do not need to memorise the range, just hold a few anchors. Across the three octaves the slider covers, these are the useful ones:
220 Hz - A3, the bottom of the range. Thick and full-bodied.
262 Hz - C4, middle C on a piano.
440 Hz - A4, the tuning reference. Close to the middle of the range.
523 Hz - C5, one octave above middle C.
880 Hz - A5, distinctly thin.
1760 Hz - A6, the top of the range. Whistle territory.
Tips
Anchor on A4 = 440 Hz. The ends of the range are A3 (220) and A6 (1760); placing the target against those three anchors gets you close fast.
Watch for octave errors. The most common mistake is the right note in the wrong octave, and in cents that is also the most expensive one.
Use headphones. Phone speakers underplay the low end, so the tone sounds higher than it is.
Hum it. Imitating the tone with your own voice is the quickest way to work out which octave you are in.
Do not burn the replays. You get three; spend the first on rough placement and save one for fine tuning.