There are two different skills that get sold under the same word. Absolute pitch — the ability to name a note with nothing to compare it to — appears to depend on early musical exposure during a critical period, and adult training programmes have a long, unhappy record of failing to install it. Relative pitch — naming the distance between two sounds, or the quality of a chord, or the shape of a loop — improves reliably at any age, for almost everyone, with modest and unglamorous amounts of practice.
What this site trains
Every drill here is a relative-pitch drill, and the design says so out loud: rounds are transposed into a key you were never told, precisely so that no absolute reference can help you. If you could name pitches outright, the drills would be trivial and useless. Because you cannot, what you are forced to attend to is the interval, the stack, and the order — which are the things that transfer to real music.
What improvement looks like
It does not look like sudden certainty. It looks like the confusion set shrinking. Early on, a minor 3rd gets answered as a major 3rd, a major 2nd, and occasionally a perfect 4th. Later the wrong answers collapse onto one neighbour, then onto the inversion, then they mostly stop. That is why the pages here publish the confusion set instead of a single accuracy percentage: the shape of the errors is the measurement, and it moves long before the score does.
The honest claim
Practising here will make you faster and more accurate at naming what you hear, and that skill will show up when you transcribe, improvise, or learn something by ear. It will not give you perfect pitch, and nothing on this site will suggest otherwise. If you want the underlying theory rather than the recognition skill, the network has a site for that; this one only asks the questions.
Why the drills hide the key
If a round announced its key, the fastest route to a correct answer would stop being recognition and start being arithmetic: read the key, read the answer options, work out which one fits. That is a theory exercise, and a good one, but it is not what an ear does in real time. Hiding the key removes the shortcut and leaves only the sound, which is why every level here transposes by its seed and why there are no per-key pages anywhere on the site.
It also has a pleasant side effect for a small site: because a distance and a stack are the same objects in every key, there is nothing to gain from publishing twelve versions of each page. Fifty-seven URLs carry the entire subject, and each one can afford to say something.
Where to start
With the interval drill, in melodic mode, on the smallest level offered — and with the expectation that the first week produces embarrassing results and the third produces a pattern. When the pattern arrives, your progress page is where you read it.