Hi there, great info about c5. I'm not really familiar with rock music, so come across it in early blues/spiritual forms where the blue third is somewhere between e natural and e flat - both major and minor sound "wrong" and the third is suppressed on fixed tuning instruments like the piano. In slide guitar open tunings (eg open G) the third is only played with the slide, which can vary the pitch into the elusive blue third.

Now here's my problem: I would like a c57 - i.e. I want to keep a dominant seventh in there - 1,5,b7. eg C,G,Bb. biab isn't recognising it as a valid chord.

Any ideas how to get a 1,5,b7 chord in biab?

Thanks very much for the help and fascinating musical knowledge..