As I sit here writing this paragraph, I can hear birds singing outside my window. What makes this bird song musical? Quite simply, the fact that it's changing. If the bird were just singing the same note, holding it on and on, it wouldn't be very interesting.
In a very real sense, change is essentially a necessity in music. So why introduce a constant?
Well, the main reason to do it is to introduce a useful contrast—sometimes consonant, sometimes dissonant—between that changing sound and the constancy of the held note.
Those held notes are called pedal points, the subject of this diary.
The Grove Dictionary of Music and Musicians defines the pedal point as
A long, sustained note held through many bars while movement continues in other parts of the piece.
The term originated with respect to the organ, as the organ has a pedal keyboard that allows an organist to hold one (or two) notes indefinitely with his feet while playing the other keyboards with his hands.
[On a related note: yes, I actually own a copy of Grove, all 29 volumes of it; I won it on eBay a couple years ago, for a price in the hundreds, not the thousands. ;) ]
As a result, most of the time, pedal points occur in the lower instruments, as in our first example (which I posted in the comments to Dumbo's Op. 27, on alternate scales), Ralph Vaughan Williams' Sancta Civitas. Here, it's in the first 30 seconds.
Vaughan Williams has written "true" solo violin parts before—see The Lark Ascending, for example—but here, note that the violin soars upwards above that constant note in the bass line. Just before this pedal point, the chorus sings of the fall of Babylon; you can think of the ruins as that pedal point, while the violin welcomes the vision of the New Jerusalem that is to come. [By the way, if you have time, you should listen to the rest of the track, and preferably the entire oratorio (it's only ~35 minutes): as Dumbo said, "Oh, this gets better as you go along..."]
. . .
Second, we'll look at the Cantus Lacrimosus ("Song of Tears"), the opening movement of Karl Jenkins' Stabat Mater. Yes, that Karl Jenkins, the guy who wrote the "A Diamond is Forever" music. You may want to strangle him for that piece, but, trust me, his recent stuff is actually quite good, even if it isn't strictly "classical" in construction.
Here, if you want to jump to the pedal point, it starts around 7:25.
Note that now the pedal point is no longer in the bass line, but in the voices. Of course, the downside to using the human voice as a pedal point is that, well, most people can't hold a single note for 90 seconds. Obviously, Jenkins doesn't even try that here; instead, he gets the effect of a single continuous note by having the singers repeat the same words, "Stabat Mater dolorosa" (The grieving Mother [i.e., Mary] stood [by the Cross]), over and over again. So, as the choir holds their notes, it is the orchestra that ebbs and flows both beneath and above them.
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Next, we have Paul Hindemith's When Lilacs Last in the Dooryard Bloom'd: A Requiem for Those We Love, which makes interesting use of pedal points.
First, there's the Introduction, from a historic performance conducted by Hindemith himself:
Hindemith begins by almost assaulting the listener with a C♯ in octaves in the cellos and basses. [When Robert Shaw performed the work at Yale to commemorate its 50th anniversary, he also added the organ—it was there, so why not?] This brooding four-minute movement is based on a single motif, played over and over again: A-C-F-E. Note that a good portion of the "brooding" nature of this movement comes from the clash between the C♯ pedal point and the C natural, a half-tone lower, in the other instruments. [For what it's worth, though, if you try playing the notes on a piano, making that note a C♯ doesn't brighten the music all that much.]
Secondly, there's the ending. See if you can spot the pedal point here.
[You can find the entire Hindemith recording on Youtube, which is a fascinating document, although I highly recommend Robert Shaw's Grammy-winning performance on Telarc.]
. . .
Finally, we have what is, in my book, arguably the best use of pedal point ever. Unfortunately, it's a work that hasn't been posted on YouTube, so I can't embed the video.
The work is Herbert Howell's Hymnus Paradisi, specifically the sixth and final movement, "Holy is the True Light."
You can find a recording of it by Chandos on Rhapsody (search for "Howells Hymnus Paradisi", and then choose one of the links that says "VI. Holy is the True Light"). That version, and my personal favorite, on Hyperion, are both on iTunes. Also, Naxos has a recording as well; if you subscribe to Naxos.com (which is $20/year for access to thousands of recordings, which is a pretty good deal), you can listen to it online.
Howells wrote Hymnus Paradisi as a private document to channel the grief he felt upon the death of his son Michael from polio in the 1930s. It was not until the 1950s that this work saw the light of day, when the aforementioned Ralph Vaughan Williams convinced Howells to publish it. While it is rarely performed in the U.S., it became quite popular in Britain; for the rest of his life, Howells received letters from listeners moved by hearing it.
The previous movement ends with a beautiful a cappella chord in D major. The finale then starts with the cellos, basses, and organ playing a low B♭, as we find ourselves in the rather interesting key of B♭ minor (the same key used to open Samuel Barber's Adagio for Strings).
B♭ minor has five flats: B♭, C, D♭, E♭, F, G♭, A♭. This might remind you of Dumbo's Op. 27 on the pentatonic scale—because, aside from the C and F, all the notes are on the black keys!
So, not surprisingly, in measure two, a trumpet comes in, heralding the brilliance of that True Light, playing that pentatonic scale. Two measures later, in comes a second trumpet, also playing that same scale. They continue on until bar 12, when the violins and violas enter. Remarkably, they hold two more notes, a D♭ and an E♭, for about two bars, creating, for a short period of time, a double pedal point, one above, and one below.
The pedal point lasts for a total of 60 bars, half of those purely orchestral, while in the second half, the chorus sings lines from the Salisbury Diurnal: "Holy is the true light, and passing wonderful. Alleluia." Over a total of about 3 minutes, the part above the pedal point builds in complexity, but remarkably, Howells continues to draw the listener's attention back to the pedal point by constantly having the harp and piano play that B♭ staccato, until the music, having reached fortissimo, spills over into a new key.
I've only had time here to highlight a few examples. But the more you listen, the more you'll be able to pick out pedal points. [In fact, I've conspicuously left out the exemplar of the pedal point given by Grove!]
And, by the way, here's one last bonus (non-classical music) clip to prove that the pedal point isn't limited to classical music.
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Unfortunately, I have to work tonight, so I won't be able to contribute much to the discussion until relatively late (close to midnight ET).