It is so important to practice with a reference tone, whether that be a piano note or another instrument holding a pedal. Today I am going to record myself playing long tones so that I can play my scales against the root. In this way, I can play back the drone and tune the 2nd, 3rd, 4th, etc. against the root of the scale. This is much more rewarding than using a tuner and much closer to "real world" playing. The same goes for lip slurs. Use that drone as the fundamental tone as you slur upwards in the overtone series. It may even make these daily drills enjoyable as you fine tune the intervals and really hear the timbre of them. Hope this helps. Additionally, the same drone can be recreated by hitting low octaves on the piano while keeping the sustain pedal down. As a trombonist, you have to twist your body so as not to hit the piano with your slide, but it is worth it. You will know if you are really playing in tune if after you are done, there are no small reverberations in the body of the piano. Get to it!
Dr. Michael Kearns
Musician, educator, husband, father, web designer ... my life is like a mosaic with each piece vying for my attention.