This work is choir music for tape, and the tape is an integral part of the opera DONNERSTAG aus LICHT, where it is played at lower volume than the live music in acts I (Michael's Youth) and III, 1st scene (Festival). During live performances of the opera, the 8-channel tape (with a duration of about 49 min.) is played through loudspeakers surrounding the audience, thereby providing a spatial enrichment of the musical experience, which otherwise mostly focuses on the happenings on the stage.

UNSICHTBARE CHÖRE is highly polyphonic. An essential aspect of the music, and one which has a main impact on its sonic signature, is that the diverse choral voices and lines simultaneously move at very dissimilar apparent speeds of musical motion (forming different time layers). In this work, Stockhausen takes this aspect to an extreme as I have encountered nowhere else in choral music. One part of the choir may sing lines of rigid character, while two other parts express themselves in vivid intertwining gestures, and a fourth one contributes to the texture with sustained notes, just to mention an example.

Other a capella works by Stockhausen, for example WELT-PARLAMENT or ENGEL-PROZESSIONEN, also employ this feature of diverse time layers in the different choral strands extensively, but to my ears not to such extremes; similar is the case with Ligeti's a capella works from the 1980s. One important reason for the extreme differences in time layers in UNSICHTBARE CHÖRE is the frequent embedding of singing of relatively sustained notes into the texture, against which other strands contrast, in addition to the differences between the strands with lively rhythms (although also in ENGEL-PROZESSIONEN sustained notes are sung, this occurs at low level as performed by a pianissimo tutti-choir, not as part of the main texture at high volume).

Another Stockhausen work for voices only, STIMMUNG for 6 vocalists, also often sounds quite extreme in its complex polyphony of vocal lines moving at different apparent speed. However, in that work there is most of the time a basic contrast between two groups of voices, one moving rather slowly and the other one relatively fast, and the added complexity mostly appears to come from different rhythms or from rhythmic shifting between the voices in those two groups, rather than from huge differences in time layers above the basic contrast slow versus fast. In UNSICHTBARE CHÖRE on the other hand there is a continuous clashing of truly multiple time layers in the music.

In general there are no big differences in volume between the choral lines. Mostly all the voice threads that are sounding contribute with comparable emphasis to the musical proceedings, without one being clearly in the background with respect to another one. That makes the friction of different choral voices, simultaneously proceeding at different apparent speeds of musical motion, central to the musical texture. This friction is put into constant and invariable presence since throughout the work the choir as a whole nearly always sings relatively loud to loud, with rather moderate variations in overall dynamics (except in the events between the sung texts, see below).

Especially in the first half of the work, the different choral lines do not always move simultaneously as a continuous web of voices. Rather, it happens frequently that the individual vocal lines enter the total texture and recede from it in certain time intervals. This highlights the friction of the different time layers even more, since each new entrance of a voice strand calls attention to itself, and thus also to its specific speed of musical motion, which clashes with the other voice strands. This clashing is frequently enhanced by attack-like entrances of voices.

UNSICHTBARE CHÖRE often sounds very massive, yet the precision of musical expression and attack always remains sharp. All this is explained by the recording technique. The composer (translated by me from Texte zur Musik, Band 8, p. 551 f.):

"I conducted the rehearsals and recordings with the choir of the WDR Cologne. For the entire work, which lasts about 50 minutes, I have copied on the 16th track of a 16-track-tape the beats of each bar with impulses. The choir was recorded on the remaining 15 tracks. With pitch differences and accents of the impulses I clarified on the click-track all bar divisions and tempi. During the recording I heard the click-track over headphones and conducted. For three weeks I rehearsed the WDR-choir in split sessions, and on that occasion the voice groups were recorded separately. Always all voices of one group sang. For example all tenors were recorded on one track, then all tenors with a second polyphonic layer on a second track, then all tenors on a third track; the same method was applied for all basses, all altos and all sopranos. At some moments I even have overlaid one voice group four times with itself.

"With this recording technique, with which everything always proceeded in perfect synchronicity, I thus realized in three weeks a rich polyphonic work. Afterwards I mixed in another studio for six weeks an 8-track version with eight loudspeakers, which stood in a circle around me in about 2 metres distance at ear level, as well as with a 16-track-playback tape machine and an 8-track recording tape machine.

"During that process, I copied voice groups on several tracks together, I balanced always standing the dynamics (which was the most time-consuming) and per formal section I changed the positions of the choral groups around me. Day after day I listened and mixed for 8 hours a new original for performances. The result is reproduced over 8 or 8 x 2 loudspeakers, located around the audience." []

"A choir could never sing a work like UNSICHTBARE CHÖRE live. At some moments up to 180 voices are synchronized. When all are present, the WDR-choir has 48 members. Also, a live performance of combined choirs could hardly ever achieve such a polyphonic synchronicity, pitch accuracy and dynamic balance as the recording of UNSICHTBARE CHÖRE posesses them. The recording technique of our time thus creates an entirely new musical quality."

Add to this mass of voices the fact that, as I mentioned above, the choir sings relatively loud to loud almost throughout, and you end up with a muscle and body of sound which is quite overwhelming.

In UNSICHTBARE CHÖRE, the highly precise presentation of multiple time layers and polyphonic strands by an at times truly massive voice texture provides the listener with a uniquely powerful and unforgettable musical experience.

The music sounds fairly dark and even ritualistic, even though the texts sung are mostly joyous. Several factors contribute to this character. The specific harmonies that are used cause a darkening of the overall colors of the different choral sections, and convey a distinctly non-Western character to the music. The bass voices have a dark fullness of sound which is frequently reminiscent of Russian choral music, but the overall effect of their combination with the other voice registers is of a far less specific color. Also, the harmonies employed give the music a somewhat more shouting character than in the typical Western "cantabile" expression of choral voices, although I hardly would call them abrasive and overtly dissonant in color, certainly not in the framework of typically modernistic expectations. Finally, the patterns of gestures also contribute to the ritualistic sound of the music. Those patterns are marked by a combination of several characteristics: the dense overlay of various gestures sung in different voice registers, the repetitive behaviour of the gestures, which in combination with their often forceful character many times makes them sound like powerful sequences of musical attack, and the constant shifting in collisions of the gestures against each other during the course of the musical proceedings. This constant shifting in addition avoids repetitions in the overall texture, and instead provides stunning complexity (for this, also listen to the very last passage for female choir alone).

The vocal colors, filled with mighty saturation, and the textures are imposing. It is a true feast for the ears.

Four texts are sung, the first, third and fourth texts in Hebrew, the second text in German. The texts are:

I. Judgement Day (from the Ascent of Moses),

II. The End of Time (from the Apocalypse of Baruch),

III. The End of Time (different text from the Apocalypse of Baruch),

IV. Hymn (from Leviticus)

Most of the time, however, the texts are not intelligible (at least as I judge from the second, German text), since the texture of voices is too dense for that. It seems that the realization is more about the idea of the texts, with the vocal texture basically led by purely abstract musical considerations.


First Text.

The basses present vocal lines of rigid motion, while alto voices sing rhythmically vivid gestures of jumping up and down the pitch scale in small, quick steps. Soprano voices sing more sustained notes, pausing in between, or alternate those gestures with shorter, regular pulses. After a while, tenors chime in, alternating between supplementing the gestures of either the soprano voices or the alto voices, but predominantly taking the side of the latter ones, with those rhythmically vivid gestures running up and down the pitch scale.

Second text.

This part starts with an extremely dense texture, erecting a true "wall of sound", in which some sections of the choir sing sustained notes, whereas others sing in rhythmic oscillations of small pitch variations. The texture then opens up when the rhythmic oscillations become pulses, with or without pitch variations, still accompanied by slowly moving lines. After this, the "wall of sound" returns for the remainder of this part, first with gestures similar to those at the beginning, and then with all kinds of combinations of those gestures with the pulse-like singing. At some points, nearly all the choral sections sing relatively sustained notes.

Third text.

This part also starts with a "wall of sound", with singing of relatively sustained notes. However, at first not prominently noticed, a section of the female choir sporadically breaks out of the texture with sudden upward interval leaps immediately returning to the pitch from where they started. When after some time the volume of the choir recedes somewhat, the leaps become more prominent in the texture, gaining in apparent force, and are repeated regularly to form a web of recurring gestures, but with low enough frequency as to allow for each of those outbreaks in interval leaps to be experienced as an individual, powerful event.

After a while two clarinets appear in the music for a few minutes (related to the events in the opera), playing moto perpetuo figures in regular patterns, and somewhat after the entrance of the clarinets, the gestures of choral singing change. Now the voices of all registers sing relatively sustained notes; male voices form a continuous web of sound while there are small breaks and restarts in the female voice strands, giving somewhat of a wave-like effect. Soon, however, the choir returns to the gestural pattern from before. Later female voice strands gain more and more freedom and rhythmic vividness when first, at some points, they sing in regular pulses of sound, heard in different apparent tempi, and finally they create a dense web of small sonic explosions in irregular rhythm.

Fourth text.

An extremely dense and massive texture of intertwining vocal lines of the female choir and the tenor section in vivid motion, above slowly moving lines in the bass voices, starts this part. After some time, the vehemence of musical motion settles a bit, while the intertwining of voices remains very dense; the tenor voices are now heard as a more separate strand. Then a pause choir is heard (see below).

After this, female voices sing in slowly moving, wave-like pulses of considerable kinetic thrust, whereas male voices sing forceful figures of separate rhythm. In the next passage, the wave-like figures in the female voices are converted from slow pulses to smooth oscillations; the male voices blend more into their singing. After a while, the rhythmic articulation of the male voices becomes more pronounced again and, resulting from this, their penetration of the overall texture. In the following passage, the apparent speeds of motion of the different voice strands created by the female choir become more disparate, and the overall texture becomes lighter. This lightening of the texture finds an endpoint when finally the female choir sings alone.

In this last, long passage the articulation switches from producing layers of sound to creating a flickering web of oscillations of sound, woven from a very dense texture of rhythmically vivid and leaping vocal lines.


The singing of the four different texts is separated by pause choirs, where mostly male voices alone sing sustained notes, with very slow changes in their phonetic expression. Those pause choirs are also heard as a short passage interrupting the singing of the fourth text. In the middle of the second text there is a pause choir specified as well, but I hear this section as a continuum of the main musical proceedings.

In addition, other sonic events are realized by the choir in between the sung texts. After the first pause choir, the choir members introduce a new unheard-of texture: Different members of the choir all help to form a web made of tongue-clicks, making it sound like trickling water, and at some points the web becomes so dense that it creates the effect of sounding like a small waterfall. This has to be heard to be believed.

After singing of the second text and pause choir, the choir members make a kind of hissing melody from sounds created by forcefully blowing through their teeth, with some further tongue clicking in the middle of it. Finally, after the singing of the third text, accompanied by sounds of other voices, the basses sing a short text in German and then very slowly count from one to thirteen; this passage forms one of the many moments of symbolic counting in the opera, and is heard there during the playing of the choral tape in conjunction with a duet between soprano and tenor. After that, the clarinets playing moto perpetuo figures in regular patterns (see above) appear again as "pause choir", and a repetition of the hissing passage leads to the singing of the fourth text.


UNSICHTBARE CHÖRE is available at (CD 31). The CD is strongly recommended to those who especially love choir music (you will not believe what you hear), to those who have or want to acquire DONNERSTAG aus LICHT (an important addition to the experience of that music) and in general to everyone who likes adventurous music that is excellent.

The recording is of high clarity, with very direct sound allowing to deeply listen into the dense textures. The singing of the WDR choir is superb, the same choir which so successfully transmits the magic of the choral textures in the first act of MONTAG aus LICHT (see my essay, in the other two acts different choirs sing). The extensive CD booklet also contains fascinating excerpts from the score, highlighting the special textures and singing techniques involved.

© Albrecht Moritz 2001, text edited 2005