For time to time I am away from home, and thus away from DB and bass guitar. But I have the possibility to get travel keyboard with me: 5-octave 66 keys keyboard, but from soft folding material - not good for piano technique training, but it is some tool to get sound. I planned to use it as an ear training device. What system and/or exercises would you suggest for such training? Something that could be later beneficial for DB playing.