“Notes with slash mark are whisper sounds of indefinite pitch.”

“(Eighth note with “x” notehead) means to pop lips (sounds like a cork popping out of a bottle) or to cluck tongue.”

“At measure 46 each singer is expected to improvise his own rhythm.”

These performance instructions, not necessarily what would would expect from a piece of choral music, appear on the first page of Pauline Oliveros’ 1961 composition Sound Patterns for Mixed Chorus. The subsequent pages of music include whispers, fluttered lips, and consonant and vowel sounds (“zzzt”, “drrrump”) distinguished by directions like “clenched teeth” and “nasal”. Naturally, the words never develop into a narrative or imagistic trajectory, as they are mostly gibberish. In contrast to the operas and sacred choral music of the twentieth century, Ms. Oliveros’ work is representative of a less recognized genre, non-narrative choral music, in which the hills and valleys of sounds become the focus rather than a story or theme. An emphasis on the possibilities of the human voice, as well as on sonic perception of these possibilities, incites an abstract experience that will never happen the same way twice (although Ms. Oliveros writes that the performance time should be “approximately 4 minutes”).

In John Cage’s Hymns & Variations, the vocal tones seem to materialize in drips and blots of varying size and duration, like raindrops against a windowpane, before evaporating into thin air. The piece, which runs to roughly twenty minutes, was composed in 1979 using subtractive techniques and chance operations on two hymns by William Billings. Cage’s ten “variations”—five each on Billings’s hymns “Old North” and “Heath”, two of the earliest examples of American four-part choral writing—consist only of vowels. The resulting stacks of pitches and silences bleed together into otherworldly, constantly morphing clouds of consonance and dissonance. In a recent performance by Ekmeles Vocal Ensemble,  the twelve vocalists struck tuning forks against their bodies and held them to their ears, reminding the audience of how randomized and difficult the music must be no matter how pretty or playful it sounded. The audience members were able to float along the notes and the spaces between them, never quite sure where they would land next.

During another recent performance, members of the Theatre of Voices sang Stockhausen’s 1968 work Stimmung while perched atop pillows in a circle on the stage around a crystal orb, each holding a microphone tuned to a low B flat drone. Throughout the work, whose title Stockhausen translated as “good psychological tuning, being well tuned together”, the six performers surrounded and built upon this drone with overtones, wheedling swarms of sounds, and garbled German and English words and phrases (“barbershop”, “Freitag”). Once again, the listeners were enveloped in an abstract tapestry of sound that could have gone on forever (though the piece is approximately seventeen times longer than Sound Patterns for Mixed Chorus, and over twice as long as Hymns & Variations). Did it mean anything? It probably depends how “well tuned” one felt with the interwoven overtones.

All of these works, which feel miraculously accidental and accidentally miraculous even now, in 2015 New York City, blur the lines between notes, between sound and silence, and between randomness and intentionality (particularly in the serial yet aleatoric process of Stimmung). These aspects come together in creating a continually surprising vehicle for listening from the human voice. The whispers, growls, murmurs, clucks, and shouts intertwine in endlessly new and challenging ways, and are often quite beautiful besides.

Less mellow is Iannis Xenakis’s Nuits of 1967-1968, another collection of vowels and consonants and silences that move along in overlapping bursts and breaths. Like Cage’s variations, the score is for twelve voices (sopranos, altos, tenors, and basses), but here the syllables merge and collide in a brash, bare dissonance. The opening moments are shocking, wrought as they are with an unidentifiable, incoherent panic. In one of the later sections, a vocalist sings “Pta Pta Pta Pta Pta” in groups of five as another sings “Ni Ni Ni Ni Ni Ni” in triplets, and so on down the line, so that the dissonance can be felt rhythmically and harmonically as well as between the clattering consonants and vowels. The extended techniques Ms. Oliveros employs can be observed here as well (“nasal”, “whispering”), and the word “clouds” appears multiple times in the score, at one point expanding out into hundreds of haphazard dots strewn across the tenor and bass parts: “Ataxic clouds of the syllable Tsi whispering (voiceless) even when varying the nuances and the timbre (sharp)”.

Perhaps the most well-known of non-narrative choral works from the mid-twentieth century would be György Ligeti’s 1966 Lux Aeterna for sixteen vocalists, which was used in the soundtrack to Stanley Kubrick’s film 2001: A Space Odyssey. Here, the micropolyphonic cluster chords expand and contract, “very gently” as indicated by Ligeti multiple times, until the final seven bars of silence. Once again the notion of time is blurred as voices come in one after the other, sometimes separated by as little as one sixteenth note at a time, and especially considering Ligeti’s directions to “Sing totally without accents; barlines have no rhythmic significance and should not be emphasized.” Although the text is taken from the traditional Roman Catholic Requiem, there is no sense of linearity in the notes themselves, which migrate across one’s consciousness as clouds of color and timbre.

These migrating clouds, atonal or atemporal in nature (with the occasional “barbershop” blurted out) show up again and again in mid-twentieth century choral music. In the absence of a horizontal plot or directionality, it can be blissful to wander among the particles, not quite liquid and not quite vapor.