Hey, Kohan here - the programmer behind Disco Samurai,
In this update we've improved custom music implementation - both BPM detection algorithm as well as UI have been improved.
Beat detection algorithm / UI overhaul
The BPM detection algorithm should now handle most of the songs correctly - so most of the time you don't even have to configure anything.
Though you will probably want to make sure that the song was configured correctly - to do so you can check if the yellow outline is pulsing to the music you hear and you can also check if the Beats (red lines) overlap with peaks/sharp changes in a waveform - on top of that you will also hear a metronome, which should overlap with the music.
Just keep in mind that some songs change BPM throughout the song - so to be sure that everything is setup correctly I suggest checking different parts of the song. In case the song changes BPM you will need to use trimming (mentioned below) to isolate a fragment with stable BPM as we don't support varying BPM in gameplay.
Trimming
If you only do the previous step the song should already work, but a lot of the time you will probably also want to trim it. The songs often have quiet parts on start/end and they definitely don't help in a rhythm game - so using trimming menu you can set the start and end points of the song to get rid of quiet parts. But It will also be helpful if you need to isolate certain part of the song - which as mentioned before - you will need to do if the song has variable BPM.
And that would be it for this update - I know it's not a lot of changes but we've been focusing on balancing and fixing bugs to make sure we deliver quality game - which by the way should be soon!