I assume you are aware that the Singing C Eb exercises are recorded on D and not Eb. This was interesting as I am trying a new mouthpiece and it set off a whole lot of tests of the intonation across the instrument as the Eb is the hardest note to get in tune at the moment. Also interesting that you say this is where a lot of people hit problems. I have had to concentrate harder on this set to maintain the C effortlessness up to the Eb as I became aware of tension. Having done book 1 and worked some of book 2 I am pressing on to find this point. I thought it was above G things changed for me but it seems the seeds are sown on Eb. Thanks for the great course. I also work a lot with singers and a lot of the ideas I use in warm up sessions with my choirs.