不 and 一 both have the property of changing tone to suit the tone of the following character.
This phenomenon is called the tonal sandhi.
What would the correct/standard tone combination for this expression be?
My thoughts are: the 4th tone on ding causes the yi to take a 2nd tone, which causes bu to take a 4th tone.
Is this correct?
For some reason 2-2-4 sounds ok to me too. Are there other variations on this?