All of the pieces contained in this recording are, to some extent, one of a kind. Certainly all would agree that there is no other piece in the repertoire that is quite like the Toccata and Fugue in d-minor, although focusing upon its obvious oddities can obscure the ways in which the piece is actually quite traditional. The point behind the title of this CD is not that every piece included is an unicum, but rather that it was part of Bach's habit to experiment with traditional understandings of the relationship between style and genre, so that a piece which represents a particular genre may show characteristics traditionally found in another genre. While several of the works contained here may be seen as unique, it is Bach himself who is “one of a kind,” in the extent of his experiments with the limitations of genre.

This particular selection of pieces, ranging from the over-familiar (Toccata and Fugue in d) to the obscure (O Lamm Gottes), was chosen for the variety of styles and textures that they represent within their respective genres, and - perhaps more importantly - to reveal the ways in which the remarkable instrument Paul Fritts has built for Pacific Lutheran University can bring this music to life. While this organ has a distinctly North German accent, its wide array of cantabile registers is especially well-suited to the chorale preludes on this disc, and its various plenum capabilities serve equally well the demands of massed homophonic sound and of intricate counterpoint.

Whether or not one believes, as some do, that the Toccata and Fugue in d-minor (BWV 565) was originally a piece for solo violin, one can hardly escape noticing the elements typical of string writing in this piece: the broken chords, arpeggiated figurations, and extended passagi. Such elements of course exist in quite a number of Bach's keyboard works, and the exposition of the fugue in particular recalls similar passages in the manualiter toccatas. But in BWV 565 there is a great deal of music consisting only of single lines and of relatively thin-textured, transparent counterpoint. Only the few moments of massive chordal writing break the transparency of texture. Because of this, one is not limited to using registrations normally best suited to such violinistic writing, combinations of principal stops—usually without mixtures; rather, here the toccata and the end of the fugue are played with the presence of sixteen-foot manual stops, and of the thirty-two foot Subbas in the pedal. A similar registration is used for the small Prelude and Fugue in e minor (BWV 533), where the extreme simplicity of the fugue subject, along with an abundance of rests and punctuating chords, allows the plenum to add strength to an otherwise rather sparse texture.

The decision to play the Prelude in e-minor (BWV 548) on a single Principal stop in the manual is not based on any conviction that the piece must be so registered, but solely on the way that the singing quality of the eight-foot Principal of the Rückpositive allows the pathos of this large-scale prelude to speak with immediacy and intensity. As such, it is intended to prepare the striking contrast brought about by the use of the full plenum for the fugue.

The chorale prelude on Erbarm’ dich mein is indeed a unicum among Bach's organ works: no other chorale prelude by Bach makes use of the homophonic accompaniment of repeated chords found here. A similar effect is found in one of the movements in the first of Kuhnau's Biblical Sonatas, where the repeated chords accompany the chorale Aus tiefer Not schrei' ich zu dir, although an even closer resemblance is found in Busbetzky's cantata on Erbarm’ dich mein. The accompaniment in Bach's work clearly imitates typical string ensemble writing, and is an ideal showcase for the Salicional register of the PLU organ, augmented by the Spielflöte. A further augmentation to this manualiter piece is provided by a little trick of registration: the chorale melody is doubled by the Nachthorn in the Pedal division, in order to bring the chorale more clearly into relief.

A similar accompanimental registration, the Spielflöte and Rohrflöte, is used for the flowing inner voices of the five-part chorale prelude upon An Wasserflüssen Babylon. The subtle contrast between this sound and that of the eight-foot Octave in the Pedal, which plays the lowest two parts, allows the complex polyphony to be heard clearly underneath the Rückpositive Principal and Dulcian, drawn together for the chorale melody in the soprano voice.

The preludes on Herr Jesu Christ, dich zu uns wend’ and Herzlich thut mich verlangen both employ registrations using a quint-flute, or nasard. The "nasard" registration of the Rückpositive is the Rohrflöte, Waldflöte, and Nasat. It is heard in Herzlich thut, accompanied by the Spielflöte of the Great and the Subbass and Principal of the Pedal. Of course it is necessary to play the Rückpositive one octave lower to obtain the correct pitches; this is a traditional practice that is documented in the eighteenth century by original registration indications as well as being suggested by the mixture compositions of certain organs of that time. In this way the capabilities of the Rückpositive for producing a sound rich in Gravität are greatly expanded. In Herr Jesu Christ, dich zu uns wend is heard the "nasard" registration of the Swell, the Bourdon and the Nasard, accompanied by the Spielflöte of the Great and the Pedal Prestant. Thus the two registrations have different characters: plaintive in the Rückpositive, and darker and more mysterious in the more remotely located Swell division. As a result, the more declamatory setting, Herzlich thut, very much in the style of Buxtehude, focuses upon the soprano voice, while the registration for Herr Jesu Christ, dich zu uns wend’ allows the movement of the inner voices to be heard without the soprano voice dominating the sound.

The combination of flutes at eight and four foot pitch in the Rückpositive was was chosen for the first verse of O Lamm Gottes, unschuldig because of the way in which their quick and supple speech responds to the details of the rather highly decorated counterpoint of the accompanying voices, allowing their movement to be both quiet and clear. By contrast, the second verse, essentially a lightly ornamented harmonization of the chorale, is give to the transparent vocality of the Rückpositive Praestant.

The agile and energetic sound of the combined 8’ plena of the Great and Rückpositive, heard only briefly elsewhere on this disk (in the middle of the Fugue in d minor) is heard above the Pedal reeds in Valet will ich dir geben, although such a registration is by no means necessary for this piece; a very similar work based upon the chorale Komm, Heiliger Geist, by Bach's contemporary, Georg Friederich Kauffmann, was published in his Harmonische Seelenlust of 1733 with indications for a registration using a Vox Humana together with flutes above a pedal registration including a Trumpet stop. Such a registration would also serve well for the Bach chorale prelude; as is often the case for Bach's chorale preludes for a single manual, with or without pedal, the plenum is only one option among many.