Pitch perfect:
A sound is played and the user must guess the note using the number row. Sharps and flats are not supported.
Press 1 through 7 for "A" to "G", then press 1 through 8 for the octave. Press backspace to repeat the note.

Time Signature:
Play a short song using tones and then ask the user the time signature using the number row.
if time signatures grater than 10 are supported, control plus number for higher numbers.
For example if it is 3/4, the user presses 3 then 4. If it is 12/3, the user presses control plus 2 then 3.

Rhythm Test:
Announce a beats per minute tempo and have the user press space 5 or 10 times. Analyze their average bpm and compare it to other challengers.

Instrument Category:
Which of these instruments is apart of the brass|woodwind|percussion family?
The user is given a list of checkboxes with instrument names and a done button to finalize their selection.

There are a lot games with music and matching sounds

Personally I'm not a fan of these challenges and i think these would be the hardest to create. But in case the developer is interested or enough people like them, I wrote them down.

Hello,

Pitch perfect:
IN fact we already have such a challenge in another form, the one where you have to repeat a short melody of a few notes. I think it's kind of a duplication.
Note also that, not so many people have perfect pitch, and even if there are certainly more among blind people than in general population, it still isn't that many, as far as I know. Being correct with a single note stays hard for many people. Trying to play a short melody as in the already existing challenge is certainly easier, since a lot more people have relative pitch or at least a little a musical ear.

Time Signature:
I'm personally not good enough at music (and AI?) to be able to generate short songs on the fly with something beyond 4/4 and 3/4.
Although I play the piano and sometimes make music, I don't know at all how to create a 6/8 music from scratch, even a short one of 10-15 seconds, for example.
I don't say that it's totally uninteresting, but clearly it's a lot harder to implement.

Rhythm Test:
This one looks more interesting, but also harder to implement.
Question: is it more important to be regular or precise ?
I don't know if you understand what I mean, I'll try to explain: Let's say that we ask for 120 BPM, who should win ? Player A who pressed spaces at times T = 0, 0.4, 0.8, 1.2 and 1.6, or player B who pressed space at T = 0, 0.4, 1, 1.6, 2 ?
A is too fast (150 BPM) but perfectuly regular, while B has globally the correct tempo but is a little off-beat.

IN fact, isn't this challenge kind of a duplication with the already existing rhythm challenge ? We can seriously ask the question. Is it different enough to be worth it ?

Note that, as for the already existing rhythm challenge, if you have an instable Internet connection with highly varying ping time, you are much more likely to lose. Some people may find it unfair.

Instrument Category:
We haven't yet MCQ with the ability to check multiple answers at once, but this could also be an interesting one.
Probably we could use the same interface for this challenge and another one proposed in another topic where you are asked whether a given game is using board/dice/cards/dominos.
Or we could imagine this challenge as being as matching exercise (i.e. match an instrument with its type), as also proposed for another challenge in another topic.
Thoughts are open, I don't know well what could be the most interesting here.

Would it be possible to waitfor the client to finish the rhythm challenge and then submit all data at once rather than after each key press? Trying to do it server side was not a good presentation. Also I think the user should press space to start reproducing the rhythm, like with simon.
Honestly I'm not a music person, so this topic really isn't for me. I just wanted to bring forth the ideas. I don't know how time signature works all that well and I'm not good with calculating rhythm. I'd say whoever has more time presses closer to what the tempo should have been for each press wins, but others might say taking the average of all presses would be better.

Also I think the user should press space to start reproducing the rhythm, like with simon.

I really don't think that's needed.
In Simon, you press Space to start, because you have a limited time to play the sequence after you hear the first and any other sounds. In other words, you're telling the game, "I'm ready to hear the first sound now."
Here, your time is unlimited, you decide whenever you want to start already, and to start, you just press the first digit at which point you started the sequence. You could start it as soon as the sequence you heard is done, or a minute later, it doesn't really make a difference.

An argument could be made that pressing space before starting would allow you to hear the sounds, but I'm not sure it's so useful, this is just 2 sounds for now, and you will probably fail on your first few tries, but once you got it, you will never need to learn the sounds again.
In Simon there are not only 5 sounds, but 2 different variations of that challenge.

On the other hand I fully agree that if we are going to have any other rhythm challenges, they need to be processed by the client, especially if they require even more precision.
This rudimentary one works relatively fine, but it can indeed be quite frustrating with even a slightly unstable ping, because it throws off the entire sequence. Maybe there should even be a button to start from scratch, of course if you haven't already pressed the last button. Sometimes I can already hear that it didn't work the way I wanted it to, so I already know the percentage will be terrible.
Normally I would say such a button makes it too easy, but taking ping issues into account...

The instrument-based challenges sound quite fun, definitely with a lot of potential.

Is it too late to adapt the existing rhythm challenge to be client side? Several people have complained about the inaccuracy. Also they said that it starts the timer while the pattern is still being played, not when you press the first button. I'm not sure if that is true or if they are just complaining and being too harsh.
How well does the rhythm challenge work on mobile devices? I haven't tried it before. Do you use the keypad to press 1 and 0? Or are there two buttons next to each other that you press?
Re: instrument challenge:
Yep I think this is a keeper. Maybe we could have another challenge where a note is played from an instrument and you select what instrument it is? Would require samples to be added at least server side, but shouldn't be too much to ask.

Also they said that it starts the timer while the pattern is still being played, not when you press the first button. I'm not sure if that is true or if they are just complaining and being too harsh.

Definitely not true. More often than not, I repeat that sequence multiple times before I even start playing it, and the timer can't even start at this point, because the time to play the first sound doesn't really define anything, what matters is after the first sound.

How well does the rhythm challenge work on mobile devices?

Generally, everything speed-based is very difficult on mobile devices, unless two people are playing on a mobile device, that's probably the only time this is useful.
You don't use the standard on-screen keypad, for all Duck racing duels of this type, you use this 3X3 grid which is also visible on the Windows client, which contains numbers from 1 to 0, space and backspace, so to make it universal for all duels.

In other words, for this challenge in particular, you are supposed to tap 1 and 0, but this is pretty much impossible to do very well, and honestly my opinion is that this isn't even fixable in any way. If there were two buttons next to each other, that would make it easier, yes, but there would be no major improvement. By the time you focus the button and double tap it with VoiceOver, you already lost your rhythm.

The only way this is fixable is one day in the distant future with a native app, where this would b a direct touch zone you can just tap to produce the sequence.
Until then, the only reason I even wanted this grid to be implemented was so the game isn't completely stuck if a touch screen player is a part of the game, now you can at least proceed and finish the duel, and it globally does work for other duels not requiring high speed such as Black jack/mine or treasure, etc...