The Preludio from Barrios’ La catedral is a beautiful example of idiomatic writing for the guitar that demonstrates good voice-leading and contrapuntal technique. It is quite easy to trace the four voices as they move through the composition in a mostly step-wise progression. Any large skips that are encountered, as in measures twenty-eight and twenty-nine for example, usually occur within the same harmony where the voices exchange chord tones or an octave displacement occurs.
As with the Allegro solemne movement, the harmony is straightforward for the most part. The piece is in B minor and makes extensive use of the ii7 chord (C#m7b5) as well as the VI7 (GMaj7), iv7 (Em7) and V7b9 (F#7b9) chords. A secondary dominant thirteenth chord (V/III) occurs in measure eight where Barrios moves temporarily into the relative major (D). The use of the tonic pedal point (open B) in measures one through seven is also noteworthy as it seems to give the music an ethereal quality.
One of the more striking harmonic features occurs in measures fourteen and fifteen where the C#7 chord (V/V) is converted into a French augmented sixth chord by lowering the G# to G natural. As a review, this chord type is known to jazz musicians as a dominant seven flat five chord and is referred to as a “tritone substitution” in which a dominant seventh chord is substituted for another dominant seventh chord with a root related by the distance of a tritone or a diminished fifth. In this case the C#7 is substituted with the G7b5. I chose to label it as an enharmonic G7b5 in keeping with our practice of showing this harmony resolving to the dominant (F#7) a half-step below. The seven flat five chord has two possible roots which are related by tritone. In other words C#7b5 and G7b5 contain the same tones.
Many times the harmonies I indicated include non-harmonic tones such as suspensions, passing tones or neighbor tones that eventually resolve but were not labeled in order to keep the analysis as clear and uncluttered as possible. For example, in measure two the upper voice (F#) is a suspension that resolves to the E in measure three to complete the chord. I did label one example of an upper neighbor tone in the bass in measure forty-three as this creates a rather modern guitar sound that I find interesting.
The use of the minor five chord in measure twenty-six (F#m) in first inversion as a passing chord between i (Bm) and VI7 (GMaj7) I find to be quite beautiful. Also the G6 chord found in measure thirty-three is interesting. It may also be heard as an Em7 since these two chords are identical, but to me it sounds more like G is the root in this case.
The pdf file below contains the score and analysis. Once again my hope is that through this type of analysis you will gain a deeper understanding of the music as well as having a practical way of understanding important harmonic principles through well known works for the guitar.