Ichi Kotsu

I guess that what your teacher means is the following. If you only talk about RO (or TSU, RE and so on) you don't specify the absolute pitch, because the pitch of RO depends on the shakuhachi that you are using: RO will be D for 8 SUN shakuhachi, but E for 6 SUN, so it is relative. On the other hand ICHI-KOTSU refers to absolute pitch and it will always mean D. So it's a useful concept in general, but also in particular when you talk to other players (koto, etc.) which don't know what pitch your RO represents.
One more thing: ICHI-KOTSU is the absolute name for the D pitch, but there are 11 other names you will have to learn to identify the remaining pitches :-)

And here are the other ones :

壱越 Ichikotsu D
断金 Dankin D # / E b
平調 Hyōjō E
勝絶 Shōzetsu F
下無 Shimomu F # / G b
双調 Sōjō G
鳬鐘 Fushō G # / A b
黄鐘 Ōshiki A
鸞鏡 Rankei A # / B b
盤渉 Banshiki B
神仙 Shinsen C
上無 Kamimu C # / D b

So, since this allows for "interoperability", the names and corresponding pitches are common to Japanese music in general, not just shakuhachi or the Tozan ryu?

Thanks Roban! That makes sense to me.

So would you say that ICHI-KOTSU is the fundamental pitch for the shakuhachi? Is this terminology (with the 11 other names) used throughout all traditional Japanese music (i.e. koto, shamisen)?

Eugene, you beat me to ask the question! I was writing the above post while you were posting

And thanks for posting the other 11 pitches, JF Lagrost. It's really helpful.

This is what I was told, but I guess this is more how it used to be in the old days. From my personal experience all the people nowadays understand very well the names of the Western pitches, so I always use them when agreement on pitch is needed. It would sound cool if you use the traditional names though

Maybe "ICHI-KOTSU is the fundamental pitch for the _standard_ shakuhachi" is a better way of putting it, because it would not be fundamental for 6 SUN shakuhachi. While ICHI-KOTSU may indeed be some kind of fundamental sound, I think it is more appropriate to call RO (whatever pitch it represents) a fundamental sound.

Strictly speaking, ichikotsu is the first of the twelve notes used in Japanese music, which was in turn derived from Chinese music. Rather than being individual notes of a scale, they are notes from which scales are constructed. This is why you have pieces with titles that include those note names that JF posted above. These names are not used to refer to discrete pitches of a scale.

Also, the Chinese notes are derived using the same intervals as the Pythagorean scale. Thus, true octaves are not possible, and technically speaking, it is erroneous to state that ichikotsu=D, but it is often referred to as such due to the fact that ro=D has become a standard for shakuhachi (not forgetting standardisation on other instruments), and also for the sake of expedience.

Nice explanation! I didn't know all these music theory details, so it's good for my background. Still, I do hope we can agree that for practical reasons it is currently fine to say that ichikotsu=D. At least this is the only sense in which I saw it referred to.

I have Chinese music background but never come across the name of 12 notes. It is either staff or softage notes.

The note characters and names are different in Chinese and Japanese, but the basis is the same. 

Kongwee, the names are also derived from music that no longer exist in that form in China any longer.
Nice discussion subject with good information provided!