Harry - You can control the bandings for numeric split-by fields by setting the view's Aggregation explicitly for the split-by column. When you do, you will see the default aggregation function for the split-by column is Histogram. Click on Histogram and you will see a drop-down allowing you to set the maximum number of intervals that will be used for the histogramming, and space allowing, for that View's numeric split-by displays as well.
I don't want to specify the number of intervals, I would like to specify the values for each interval - so if for example Omniscope bands results as 5-10, 10-30,30 - 60 etc I want to specify the band values myself and change for example to specific values 5-9, 11 - 20 etc
Harry - To specify custom intervals, create a new formulae column that tests the values and assigns each to a new pre-defined interval value. This is known as 'bucketing' (UK) or 'binning' (US) your values. This type of formula is set forth on the Useful Formulae page: