F Tenor conversion - Why D# to Db?

[4to5to6]

I understand that to convert a TT or BT to a “F Tenor” instrument that you swap the B and Bb reeds and file the D# reed bellys to go down a whole step to Db.  
 

The idea behind a F Tenor is that you can play all the normal fingerings down a row the same way you would play on a regular “C Tenor” but now you are playing down a 5th so playing the key of C is actually the key of F and so on.  This is done to get a richer, deeper and fuller sound.

 

In someways this is the same idea as a Baritone except you are staying in the same key but sounding an entire octave lower.  This makes playing an octave lower easy as you don’t have to transpose.

 

So here’s my question..,

 

I can easily understand the B and Bb swap (the key of F has a Bb) but why the D# to Db change?  D# doesn’t show up until you play in the key of E (4 sharps) and Db until you play in the key of Ab (4 flats).

 

I’m sure it’s has something to do with the bit odd layout of the sharps and flats with the enharmonics as obvious when you play up and down a chromatic scale.  Hmm…. Maybe it is so you can keep the exact same chromatic scale fingering pattern on a F Tenor as if you were playing a chromatic scale on a regular C Tenor instrument.  Did I just answer my own question???

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Edited July 31, 2023 by 4to5to6

[Little John]

3 hours ago, 4to5to6 said:

I can easily understand the B and Bb swap (the key of F has a Bb) but why the D# to Db change?

 

A true F tenor is a transposing instrument. When you finger a C scale it sounds as an F scale a fifth lower. But the score you are playing from would be written in C. (The same as a French Horn in an orchestra. Most brass instruments are transposing instruments, but usually in Bb or Eb.)

 

So you're thinking in C but sounding in F. An English concertina is designed with four sharps and three flats. To maintain that as written the the Db should be changed to D#. As sounding that is changing Gb to G#.

 

Does it matter? My C bass is actually a converted F bass. The Bs and Bbs (as sounding) have been swapped but the Dbs (as sounding) have never been re-tunes to D#. Only once has it caused me any difficulty.

 

LJ

 

PS If a TT is changed to an F tenor in this way it's not a "true" F tenor because the notes are displaced one row from where they would otherwise be.