What does 本調子 mean in a musical context?

Question

When looking at musical instruments online ([篠笛]{しのぶえ} and 竹笛{たけぶえ} in particular, but I guess this goes for more instruments), their 本調子 is always listed. Some flutes are ６本調子, some ７本調子 and some even ８本調子.

When looking the word up on JDIC it says either:

• normal condition
• keynote;  proper key;

The first translation seems illogical ('6 normal condition'), plus I've never heard of the term 'proper key' (and although English is not my native language, google doesn't yield much either). If it's just the key of the instrument, I don't see why numbers are being used to denote it. As far as I'm aware, Japan doesn't label musical notes by number.

When looking up 調子, the result is this enumeration of pretty much every musical quality out there. Once again, not helpful.

• tune;  tone;  key;  pitch;  time;  rhythm

Any musically minded people out there?

Answer 1

This refers to the base pitch of the instrument. 調子 refers to the tuning of an instrument, and the number is the type of tuning. Each number represents a semitone increase above the base key of low F, with F being 1. So if you have a 六本調子, you have a Bb flute (F F# G G# A Bb (A#)). The others change accordingly.

On a side note, there is a word 一本調子 that carries the meaning "monotonous" in the sense that we use it in English, as in a monotonous (or boring) speech.

This site has some really good explanations if you want more information.