Timbre and Spectrum

The whole piece, when viewed in a time-intensity display shows a very balanced set of peaks. The long opening section is well-balanced with the coda.

Figure: Atmosphères Time-intensity view of the complete piece.

37#37

The section analyzed in this essay shows a regular crescendo shape.

Figure: View of the section analyzed. After the stopping of the cluster in the double-basses the 48-voice polyphony builds up a big crescendo.

38#38

Orchestrated for the strings section alone the passage is intended for a very homogeneous timbre. Except for the ``shrinking'' effect towards the end of the section, during the crescendo there is not any notable range shift. The ``cloud'' remain ``stationary'' in its outer design.

However, inside the homogeneous orchestral strings timbre, a subtle ``coloring'' effect is created.

The section starts sul tasto and con sordino. Mutes (sourdines) will remain on up to the end of the crescendo.

Playing sul tasto gives the section its distinctive color. Then, at bars: 49-50; violins I, II and the cellos start getting one by one (beginning from the second violins) to play sul ponticello. A gradual shift of sound-color occurs.

This shift is notated as a very detailed process. It starts at the second violins then it ``spreads'' to the cello section and almost at the same time, starting from the Violin-I N.14 and going up to Violin-I N.1 it creates a gradual change in sound-color, as if the acoustical output from the orchestra was miked (recorded) and then modified, filtered through an electronic device.

The process is wanted to be really continuous, so when Violins I are getting ``more and more'' on ponticello, at the same time, cellos are getting back to normal playing position. This is noted poco a poco ord. in the score (bar: 49).

This color-shifting is also emphasized by the entrance of the Double Bass section in a cluster-like chord sul tasto and pppp at bar: 49.

From this time on, ponticello and normal playing is alternatively distributed among sections.

This creates a rather unique sound-effect which is best described by Ligeti himself:[1]

One gets an additional subtlety in the timbre aspect by modifying the playing techniques. [...] By arranging to have not all instruments playing ``normal'' or sul tasto at the same time, there is a diagonal shift such as at every moment another part of the texture is lightened by the ``metallic'' ray. [the apparition of higher frequency components in sul tasto playing] The indications appear on every instrumental part, but due to the great number of parts, we get an illusion of a continual transformation [of the timbre].

Sonogram and spectral views of an audio recording of the section show the gradual increase of higher frequency components created by the increase of ponticello playing.

Figure: Sonogram view of the micropolyphonic section. Darkened areas show a condensation in the high frequencies at those times when several instruments are playing ponticello.

39#39

Inside the thick compact ``cloud'' of sound shown here, the region from around 6,120 to 12,139Hz. is the overtones harmonic structure created by ``normal'' playing. The actual playing take place much lower than those frequencies, in around 200 to 1,600Hz. for a violin.

Figure: Spectral view of the same section. The jagged area also shows the increase in ponticello playing.

40#40

Even though neither a sonogram nor a spectral view can accurately display changes in performing techniques, for they can only show changes in the resulting spectrum of all the music (and the ambient noise), the darkened vertical bars shown in the Figure: 3.20 and the area with an increase of jagged lines in the Figure: 3.21 nevertheless display an increase in the amount of higher frequencies created by an augmentation of the instruments shifting to ponticello playing.