add 'mix in key' mode, toggle by longpressing 'match_key'

[Frank Breitling]

In Mixxx 2.2.4 it is not possible to turn on key sync by pressing the 'match' button long.
It is a not only annoying to remember to press the match button for every new song but it is also a source for error.
It would be important to make the match button a witch like beat sync.
Beat sync can be easily switch on by pressing the 'sync' button long.

I am running Mixxx on Windows 10.

[Frank Breitling (frank-breitling)]

Also Rekordbox names this function key sync in analogy to beat sync.
Maybe it would be nice to use a common name for this function and rename it.

[Be (be.ing)]

Key sync is what it is already called in Mixxx.

[Frank Breitling (frank-breitling)]

Ok, but the button is labeled 'match' not 'sync'.

[Owen Williams (ywwg)]

Would we use lancelot key compatibility? (i.e., either exact match or one number or letter different)

[Frank Breitling (frank-breitling)]

I don't know.
But here I just requested to turn the button into a switch.
I didn't see any problems with the current key sync behavior.
Changes to the key sync behavior should be a separate issue.

[Owen Williams (ywwg)]

There would be new code required to decide how to do key sync lock -- would it be sufficient to just match key on track load?

[Owen Williams (ywwg)]

(Not asking you, Frank, just thinking out loud)

[Frank Breitling (frank-breitling)]

Alright Owen, thanks for your thought.
I think that is exactly what should happen and what happens in Rekordbox.
... as if on every track load this key is pressed automatically because doing it manually is boring and is easy to forget.

[Daniel Schürmann (daschuer)]

Such a sync key mode has some implications we need to consider.

Currently Mixxx shows the most common key. It is normal that the key changes during a track.
There is also the issue that there is nothing like "the key" that you can detect. Mixxx detect the probability of all keys looking at the frequency of notes, than decides for the key with the most compatible notes.

So I think based on the current detection results, it needs human support to produce a reasonable good harmonic Mixxx.

I can imagine that a latching sync key button will do many odd things currently.
Once we have changing key support and a detection based on chords, such a latching mode makes much more sense.

Maybe we should postpone the feature to that point.

[Frank Breitling (frank-breitling)]

You can worry about these details and fancy algorithms later.
For now just make the button auto press at track load.
Nobody has to enable it, if one is unhappy with the result.
However, many people don't like to press it again and again.

[Daniel Schürmann (daschuer)]

For me it does not make sense to do the effort now.
If you like to jump in to make it happen before, I am happy to receive a PR. Here are some hints: https://github.com/mixxxdj/mixxx/wiki/Bugfix-Workflow
If you have questions, just ask at https://mixxx.zulipchat.com/

[Owen Williams (ywwg)]

I don't think it's necessary for the feature to be perfect before we can think about implementing it. You say you want Mixxx to track key changes, I think that's a rabbit hole with no end. What about songs with complex chord progressions or non-western tonality? We can't account for everything, and just because we can imagine cases where it won't be perfect doesn't mean it won't be useful much of the time.

If rekordbox does something simple, we can do the same. Just match keys based on the library on track load. Maybe it won't sound perfect, but it provides a starting point for the DJ. They can tweak or reset the key adjustment if they want. If, later, we want to enhance the feature, we can. Better to launch and iterate.

[Owen Williams (ywwg)]

I agree with daniel, this isn't a priority for us but it would be a good starter bug for someone.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/10129