Chorale Tune in Soprano. In pieces for two manuals, you can choose the sweet-sounding principal 8’ stop with or without the tremulant which helps to bring out the melody. Sometimes doubling it with a gentle Salicional, undulating Unda Maris or Voce Umana will produce a very gentle affect. The accompanying voices can be played on a different manual with one or several flute stops. The pedal sounds best if played with gentle 16’ and 8’ stops of the flute family. Depending on the balance and volume level, you can use Principal 16’ instead of the Subbass 16’.
If you want a more colorful registration, you can play the soprano with either solo reed (such as Oboe, Krummhorn with or without the flute 8’) or combination of compound mutation stops. One of the more popular solutions would be to use Cornet of 5 ranks. Generally speaking, if no separate Cornet is available in your organ, you can try building it yourself, by adding flute stops of 8’, 4’, 2 2/3’, 2’, and 1 3/5’. The volume level for balance between the parts of such combination could be adjusted by the means of the swell pedal, if present.
If your Bach chorale prelude is a one-manual piece, then depending on the character you have many options, from a single flute stop, two flutes of 8’ and 4’ pitch level, principal registrations, such as Principal 8’, Principals 8’ and 4’, Principals 8’, 4’, 2’ and even up to full principal chorus with mixtures and with the reeds of 16’ in the pedal.
In a manualiter composition more exotic but nevertheless very colorful registration would be playing it with a single reed stop, such as Vox Humana 8’ or even a Trompete 8’. Do not neglect the power of a single 4’ flute, if your chorale prelude is of lively but gentle character.
Chorale Tune in the Alto. This version of the chorale prelude (Christum Wir sollen loben schon, BWV 611) could be played on the single principal 8’ or two principals 8’ and 4’. There is an opinion that the tune could be played on a separate manual but apparently Bach intentionally constructed the piece in such a way that the polyphony would obstruct the hearing of the tune. The pedal part in this piece could be played using 16’ and 8’ principals but a few ending measures featuring the double pedal suggest that only Principal 8’ might be sufficient here.
Chorale Tune in the Tenor. The most common solution in such chorale preludes would be to use the reed stop, such as Trompete 8’ for the melody (either in the left hand part or the pedal). The top accompanying voices will sound well on Principal 8’ or 8’ and 4’ and the bass will need 16’ as a basis. If played by the pedals, this part will sound nice on 16’ and 8’ principals. The same could be said about the version when this part is played by the left hand. However, often fast-moving bass part will sound very impressive if you play it with a 16’ reed, such as Fagotto 16’ with the left hand.
Chorale Tune in the Bass. The chorale preludes featuring the tune in the bass are usually played with the full principal chorus registration with mixtures and reeds in the pedal. I discussed this option in the article about registration in playing free works of Bach (preludes, fugues, fantasias, and toccatas) so you can refer to it now.
When deciding on the registration, I always recommend you take a look at the text of the chorale in original German and find an English translation, if needed. From reading the words you will be able to appreciate the character of the piece better which will influence your decision of choosing the appropriate registration.
The are many more tips and advice that could be given about choosing registration while playing Bach organ chorale preludes but the above list can serve as a good introduction. If you want more thorough and comprehensive treatment of this topic with citations from contemporary sources, I highly recommend The Registration of Baroque Organ Music by Barbara Owen.
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