​Perhaps unsurprisingly then, the manual method for frequency tracking proved to be the most effective of those explored.
It could be argued that manual designation of the band pass frequencies adds a ‘human’ layer to the process in contradiction to the eco-structural aims of deriving all data from the environment itself. However, the process is no less of an intervention than choosing sonic features to be emulated by acoustic instruments and indeed, in this case, was achived through similar means: visual detection of features from a spectrogram. The approach is perhaps analogous to the ‘Cocktail Party Effect’ (Pollack, I. and J. Pickett. 1957. “Cocktail Party Effect”. Journal of the Acoustical Society of America 29 p. 1262) a feature of the human auditory perception in which conscious auditory attention allows for pre-semantic attenuation of signals in a complex environment.

Nature Forms II (2015) explores the possibility of recursive re-interrogation of a field recording through visualization and resonification/resynthesis via machine and performative means. In Nature Forms II a range of forms of representation are  used including semantic graphical notation, percussion notation and a hybrid form of sonogram notation. This most literal form of representation is the process I have previously termed the “spectral trace” in which notation is drawn directly onto the spectrogram to represent features of the field recording to be performed by an ensemble of flute (orange), clarinet (red), viola (green) and cello (blue).

“Spectral Trace” notation from Nature Forms II

The graphical symbols are presented on a proportional staff created to solve the problem that horizontally, the spectral trace is temporally proportional and performing with precision can be achieved through a scrolling score, however it is also vertically proportional – each pitch occupies a distinct vertical spatial position.

​Subtractive synthesis was also employed by using frequency and amplitude detected in the recording to bandpass white-noise. At the opening of Nature Forms II “coloured noise” performed by the instrumentalists is gradually shaped into the sonic structure of the field recording using subtractive synthesis, and then cross-faded with the source recording.

Nature Forms II explores the notion of eco-structuralism, maintaining what Opie and Brown (2006) term the “primary rules” of “environmentally-based musical composition”: that “structures must be derived from natural sound sources” and that “structural data must remain in series”.
The structure of the original work is conserved using the approach discussed in the miracle of the rose, where the temporal proportionality of the recording is retained by aligning multiple notation and resynthesis versions of the recording in visual representations that can be alternated or combined in the creation process of the score, processing and fixed media.
The work also uses “spectral freezing” of components of the field recording to create spectrally derived chords from features of the recording bird sounds and a rusty gate which are then transcribed into notation for the instrumentalists and temporal manipulation of the recording to allow complex bird calls to be emulated in a human time-scale.

Visual representation of temporally proportional alignment of multiple resynthesis (a.- e.) and notation (e. – h) versions of the recording in Nature Forms II (excerpt): a. field recording spectrogram; b. additive synthesis spectrogram; c. ring modulation resythesis spectrogram; d. subtractive synthesis spectrogram; e. spectral “freeze” sonogram/score f. “lyre- bird score; g. “semantics of redaction” score; and h. “spectral trace” score. 

Recording generated with data from the source field recording using additive, subtractive and ring modulation resynthesis.

to commemorate the 50th anniversary of Varésè' death a work was created using the composer's percussion work Ionisation as a source. Apart from alluding to the origin of the piece from the residue of a Varésè work, the title uses terms from particle physics which perhaps bear the same  "fantastic" qualities  in our own time that the term ionisation did in 1931. 
In theory residual drift could be performed in conjunction with a performance of the source work. A sonogram of a recording of Ionisation was used to generate a score and accompanying pre-recorded electronics. The image of the sonogram was rendered in illustrator focussing on the range of the bass flute C2-around C4. Because sonograms are probably least effective at visualizing percussive works, features such as snare drum rolls appear as continuous pitches. This deficit was put to use in transforming Ionisation into a score for a solo instrument that makes its sound through "continuous" (as opposed to discrete) actions. The first few seconds of the Ionisation sonogram and the score of residual drift are shown below (note the "piano roll" style pitch indication is used as a "playhead" for the scrolling score to orientate the performer.

Unfortunately in this case I was unable to develop a satisfactory accommodation between the degree of detail in the score and the scroll-rate required to read it: if it was over-detailed it had to move too quickly to accurately read. For the first performance a simplified sonogram score (below) was used with a pitch-guide fixed at the left of the page. The pitch-guide replaced the single-line "playhead" that is used in most scrolling scores in the Decibel Scoreplayer. I had used the same approach  to read Percy Grainger's Free music in the mac version of the score player (and this had later been coded into the iOS version by Aaron Wyatt. The pitch-guide had the advantage of providing more detail to the performers more "morphological" information about the sonic shapes and could also be scrolled more slowly than a conventional score. However in this version each player was allowed to choose which shape they would render with their instrument.

The (possibly) final version of the score identifies sounds to be performed by each performer (bass flute - red, bass clarinet - green) and contains text annotations and hue variations to represent different timbres. Since the parts are more defined the  full (unsimplified) sonogram is able to be re-added giving the performers a greater indication of the context in which their sounds are heard.

Forty percent of the summer Arctic sea ice melts, and here we’re literally watching the death throes of the planet, and these corporations, like Shell, look at it as a business opportunity.   (Hedges, C. (2013) Rise Up or Die. Truthdig)

In 1979, a military team arrived to gather up contaminated soil and debris, mixing it with cement and piling the sludge into a 350-foot-wide blast crater on Runit Island in the atoll's east. When the mound reached 25 feet high, army engineers covered it with a saucer-shaped concrete cap. A 2008 field survey of the Cactus Dome noted that 219 of its 357 concrete panels contained defects such as cracks, chips, and vegetation taking root in joints. (Atlas Obscura (2013). Cactus Dome: A Concrete Cap for a Nuclear Crater. Slate)

Other contributors to the jellyfish boom are the “dead zones” created by what scientists call “eutrophication.” That’s when farming pesticides and sewage pumped into rivers meet the ocean. Japan’s now-annual bloom of Nomura jellyfish, which each grow to be the size of large refrigerator, capsized and sank a 10-ton trawler when the fishermen tried to haul up a net full of them. (Guilford, G.(2013). Jellyfish are taking over the seas, and it might be too late to stop them. QZ)

Our first observations of elevated methane levels, about ten times higher than in background seawater, were documented . . . we discovered over 100 new methane seep sites… If even a small fraction of Arctic sea floor carbon is released to the atmosphere, we're f'd. a feedback loop where warming seas release methane that causes warming that releases more methane that causes more warming, on and on until the planet is incompatible with human life. (Jason Box)
Richardson, J. H. (2015) When the End of Human Civilization Is Your Day Job. Esquire.   

Captain Moore had wandered into a sump where nearly everything that blows into the water from half the Pacific Rim eventually ends up, spiraling slowly toward a widening horror of industrial excretion. For a week, Moore and his crew found themselves crossing a sea the size of a small continent, covered with floating refuse. It was not unlike an Arctic vessel pushing through chunks of brash ice, except what was bobbing around them was a fright of cups, bottle caps, tangles of fish netting and monofilament line, bits of polystyrene packaging, six-pack rings, spent balloons, filmy scraps of sandwich wrap, and limp plastic bags that defied counting. p. 121
There is more plastic by weight than plankton on the ocean's surface. p. 124
By 2005, Moore was referring to the gyrating Pacific dump as 10 mil­ lion square miles—nearly the size of Africa. p. 125
"Except for a small amount that's been incinerated," says Tony Andrady the oracle, "every bit of plastic manufactured in the world for the last 50 years or so still remains. p. 126 ( Weisman, A. (2007). The Earth Without Us. Thomas Dunn: New York)