Tsu meri in the second octave.

Tough question, Felix. Here are my 2 cents:
1) Get a tuner and use it while practising to make sure you produce the right pitch.
2) Experiment with various degrees of lowering your chin and various levels of opening the 4th hole. Basically the more you lower the chin the more you can open the hole and viceversa.
3) Once you find the combination that suits you most, make your body remember it by practising again and again, and also remember the pitch so that you can make fine adjustments even when you don't have a tuner.

From my own experience, it is better to be able to produce the right pitch without lowering your chin too much, so that you can play tsu meri easily even when it is part of a melody. This means you should try to open the 4th hole as little as possible, which is usually done by a kind of rotation movement of your finger.

By the way, I have to admit that I find tsu meri challenging both in first and second octaves, so I am not sure if you are talking about any additional difficulties that you encounter in the second octave. One thing that is sure is that it is easier to spot the wrong pitch in the second octave because of the higher frequencies involved, so more care is needed when playing.

Good luck!

Thanks for that, mate!
I guess it's just practice, practice, practice! But is there a "holding back" of breath to facilitate hitting the note, because when I hear it played it sometimes seems almost "muted"?

The sound intensity of tsu meri will be lower than for let's say ro due to the physics of opening only slightly the 4th hole. You can produce a louder note by opening more the 4th hole, which means you have to lower your chin more ("meri") to still produce the right pitch, but this only works up to a certain point, because too much meri will cut the air flow into the shakuhachi.

As I was saying in the previous post I recommend opening the 4th hole only slightly for practical reasons, therefore a quiet tsu meri is normal. Moreover this specific tone color is both expected and desired in honkyoku, so there is no need to change it. For modern works you may want to have more similar tone colors for all pitches, and what most people do in this case is to use a 7-hole shakuhachi (which also allows for faster execution of the notes that are challlenging on the 5-hole shakuhachi).

As for holding back the breath, you could use it when playing to make sure that if the pitch you are producing is not right the difference will not be too striking. Actually my teacher used to say that it is better to make no sound when playing tsu meri instead of playing the wrong pitch. This is because the wrong pitch will change more the melody than a short quiet moment, so it is more annoying to the listener.

Thanks for two very informative replies, Roban. I appreciate it!
Your last point about your teacher and the "short, quiet moment" is so clever in its simplicity, and in a sense takes the "worry" out of the piece as I approach the note.
Thanks again!

Hi Felix,
There is a useful video on this by Perry Yung, made for one of his students, on YouTube:
https://m.youtube.com/watch?v=gX4IQutzQc4

What Roban says is useful, though I was slightly confused as he calls the first hole (tsu: when open) the 'fourth' hole...

I would add that practicing in front of a mirror is really useful as it often difficult to gauge just how open that hole is.

Nice link, Paul. Cheers.
Perry Yung is a generous soul.

Hi Paul,
Sorry for the confusion. You are right, I should have said first hole not fourth, I got the numbering mixed up. Nevertheless the explanation still holds.
The video from Perry Young is also nice, as he actually demonstrates the techniques I was writing about.
Thanks,
Roban