This app was mentioned in 13 comments, with an average of 1.62 upvotes
Yup, this one:
https://play.google.com/store/apps/details?id=de.smartchord.droid&hl=en_US
They were playing around with different tiers of product, and I got it on special when it was being developed. I don't know if they're doing specials or anything now.
There's a great android app that has that already built into it's circle of fifths. The chords in a key are highlighted and change as you spin the wheel. It's called Smartchord. Great resource, it includes, scales, keys, tuner, metronome, chords, just about everything you need. One of my favorite apps by far. Not sure if it's available for Apple.
There's a great app called Smart Chords for android that has a like 30 different tools for learning scales, chords, arpeggios, progressions, ear training, intervals, fretboard, tuner, metronome etc. There's a free version or the paid one is like $25 for the whole thing forever. Was definitely worth it for me, and it was the best one I found after trying a lot of different apps.
I'm not plugging this app, but I use SmartChord on my android phone. Works great for either looking up chords or naming chords. Can be a little complex for beginners, but once you get the hang of it, you won't look back.
I've been using this guitar app for quite a long time for learning music theory
https://play.google.com/store/apps/details?id=de.smartchord.droid&hl=en_IN
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It has a ton of information related to scales, chords etc...
The UI does need a bit of getting used to though
Get SmartChord - you don't need 10 different apps for a tuner, for scales, for metronome. This is all in one.
When you tune your strings, start with the tuner, sure. BUT once you're done take a few seconds and play each pair of adjacent strings together, so that you train your ear to remember how they sound. Over time this will lessen your dependence on the tuner significantly.
If anyone tells you "Practice makes perfect", walk away. Practice makes permanent. Do not ever force yourself into rote repetition for hours at a time, because you'll just be training yourself to repeat mistakes unless your practice regimen is flawless - and no one's flawless. Stop, take a breath, and spend a few minutes working on the clarity of your sound. Play slow, get your timing right. It is far more important to play slowly and cleanly, and in time, than to be able to play fast.
I use SmartChord I'm still a beginner and am still learning my way through. Tuner works great on my note5, plenty of chord diagrams with alternate formations (though a couple times I've found a printout a buddy gave me has easier formations than the app recommends) and it has a metronome. It also has a bunch of other features. It's free and all of the above works. There is also an upgrade for a small fee that unlocks a ton of other tools, though I haven't gotten to where I need the upgrade yet.
For guitar (or bass or most string instruments commonly found in western popular music) there's Smart Chord (I don't know if this link will work), which despite its name has a lot of useful features other than just chords. I don't know if it is available for iOS, though.
Unfortunately some of the features have been restricted to the paid version recently, but it is still useful anyway.
I can recommend "smart Chords & tools" on mobiles. You can easily grab it from Google Play Not sure if there is an Iphone version, though.
Edit: link provided
Focus above all on ear training, as you mentioned in another comment that you used to play and can still read, that's going to help a lot.
I strongly recommend SmartChord for the one phone app to rule them all. Metronome, tuner, scales, ear training, and practically any feature you might think you need. Absolutely worth paying for - there's an option for a lifetime purchase as well.
There are a lot of viola transcriptions on IMSLP.org, but I would recommend getting MuseScore and doing transcriptions manually for yourself whenever you can - this should help you get back into the theory of things and reinforce your sight reading. And you can have the computer play the music with/without a metronome, to practice alongside. You can always check in case the music has already been transcribed for other instruments on the MuseScore site, and transpose it to alto clef in MuseScore.
The MuseScore phone app is useful to practice with once you have some transcriptions to follow and your computer might not be available.
I recently saw this app for training pitch but I've never used it - supposedly it can work for any instrument and track your progress.
For apple, no clue sorry
for windows:
Synthesia - http://www.synthesiagame.com/
Rocksmith to tab - http://www.rocksmithtotab.de/
GuitarPro - https://www.guitar-pro.com/en/index.php
Also for Android,
smart Chords & tools Pro version (paid app) - Mobile link
Pitchlab Pro (paid app) - Mobile link
Guitarpro mobile (paid app) - Mobile link
To improvise and write music you need to learn some theory (scales, intervals, etc) and to train your ears. I'm not expert, but in my experience, you need to chose 1-2 musical scales, on which to concentrate on start (for example i have started from minor, minor pentatonic and blues pentatonic), and practice it. It helps me to use application for android (for examples: smart Chords & tools, GuitarScales, Musical Intervals, Guitar Ear Trainer, EarTraining). If you use iOS, i think you will find similar apps.
And of course listen to music and try to remember what you liked and try to play it.