Spectrograph

This second part contains these chapters, in two files:

1 Chemistry: Reading Spectrograms
2 Performance Art: Problems of Documentation
3 Field Geology: Deductions from Beach Stones
4 Economics: Sirens in Classics, in Philosophy, and in Economic Theory
5 Linguistics: Medieval Irish Color Terms
6 Astrophysics: Doppler Tomography of Accretion Disks
7 Law: Video-game Technology in the Irish Bloody Sunday Tribunal
8 Computer Science: Visualizing the Internet
9 Occupational Therapy: Exercises in Doing, Being, and Becoming
10 Speech and Hearing Science: Speech Spectrograms
11 Restorative Dentistry: Matching Colours in Porcelain Crowns
12 Radio Astronomy: Observations of the Galactic Center
13 Archaeology: Imaging and Mapping Practices
14 Mapping: Uses of Geological Maps
15 Art History: Iconographic Analysis
16 Civil Engineering: A High Resolution Aerial Photograph

Originally published as Visual Practices Across the University, with contributions by thirty-five scholars (Munich: Wilhelm Fink Verlag, 2007).

Laptop composition – the creation and performance of music primarily using laptop computers – emerged as an important musical activity in the last decade of the twentieth century. While much has been written about the cultural and conceptual significance of this new music, less has been published regarding the sonic structure of specific works. This article explores the musical structure and design of compositions by three laptop composers at the turn of the millennium: 'Untitled #2' by Oval (Markus Popp), 'Cow Cow' by Merzbow (Masami Akita), and 'Powerbookfiend' by Kid606 (Miguel De Pedro). Each piece is analysed using spectrographic images, representations of musical sound that allow for the precise measurement of frequency and intensity. Repetition and noise are revealed as musical characteristics common to all three pieces, defining both smaller-scale patterns and large-scale designs. Using the conceptual vocabulary of Paul Virilio and Gilles Deleuze, repetition and noise are framed in relation to a 'machine aesthetic' and 'difference and repetition'. With the turn of the millennium computer music has become ubiquitous. Advances in computer technology allow composers not only to distribute their music more widely (by creating sound files for instant dissemination or posting on the internet) but also to create and shape sound itself into seemingly infinite forms. From this plethora of sonic bits and bytes a new generation of composers has emerged. These composers perform in concert and create recorded tracks using the laptop computer as their primary instrument.

This paper discusses music analysis in relation to images of musical sound using spectral or Fourier analysis.  Fourier analysis allows us to make pictures of musical performances, which reveal the fundamental, overtones, and complex noise-like sounds.  These images provide an acoustic basis for our musical perceptions.  The recent history of Fourier analysis in relation to musical analysis is discussed first, and then three analyses are presented using works from a variety of periods and cultures, including a prelude by Chopin, a Japanese gagaku work, and a computer piece by Markus Popp.  Chopin is discussed in relation to comparative performances, Japanese gagaku is explored in relation to timbre, and Markus Popp is looked at in relation to non-notated electronic music.  Each work highlights a specific approach that can be taken using spectral or Fourier analysis.

This paper reveals concordances between pitch space and vowel sounds in Hildegard von Bingen’s O rubor sanguinis. The antiphon not only displays a cogent pitch and register structure, but also projects a vivid timbre design created through the vowels of the text. I argue that vowel sounds correspond to, and help corroborate, the antiphon’s progression through pitch space—thus both vowel sounds and pitch space work in tandem to express the imagery and meaning of the text. I begin by discussing medieval language and music connections as revealed through current research as well as in medieval theoretical treatises. Next, I discuss the concept of tetrachordal pitch space as understood during the twelfth century, highlighting specific links between vowel sounds and these tetrachordal regions in the antiphon. Two performances of the antiphon are then compared using computer images, or spectrographs, which display the physical sonic profile of the combined vowel and pitch sounds. These images demonstrate how specific language-sound transformations seen in the text are also reflected in the musical timbre of the performances. Throughout my analysis I explore the domain of semantics, identifying ways in which the music’s pitch space and language sounds help express the meaning of the words.

Optical frequency combs (OFC) constitute an array of phase-correlated equidistant spectral lines with nearly equal intensities over a broad spectral range. The adaptations of combs generated in mode-locked lasers proved to be highly efficient for the calibration of high-resolution (resolving power > 50000) astronomical spectrographs. The observation of different galaxy structures or the studies of the Milky Way are done using instruments in the low- and medium resolution range. To such instruments belong, for instance, the Multi Unit Spectroscopic Explorer (MUSE) being developed for the Very Large Telescope (VLT) of the European Southern Observatory (ESO) and the 4-metre Multi-Object Spectroscopic Telescope (4MOST) being in development for the ESO VISTA 4.1 m Telescope. The existing adaptations of OFC from mode-locked lasers are not resolvable by these instruments.

Within this work, a fibre-based approach for generation of OFC specifically in the low- and medium resolution range is studied numerically. This approach consists of three optical fibres that are fed by two equally intense continuous-wave (CW) lasers. The first fibre is a conventional single-mode fibre, the second one is a suitably pumped amplifying Erbium-doped fibre with anomalous dispersion, and the third one is a low-dispersion highly nonlinear optical fibre. The evolution of a frequency comb in this system is governed by the following processes: as the two initial CW-laser waves with different frequencies propagate through the first fibre, they generate an initial comb via a cascade of four-wave mixing processes. The frequency components of the comb are phase-correlated with the original laser lines and have a frequency spacing that is equal to the initial laser frequency separation (LFS), i.e. the difference in the laser frequencies. In the time domain, a train of pre-compressed pulses with widths of a few pico-seconds arises out of the initial bichromatic deeply-modulated cosine-wave. These pulses undergo strong compression in the subsequent amplifying Erbium-doped fibre: sub-100 fs pulses with broad OFC spectra are formed. In the following low-dispersion highly nonlinear fibre, the OFC experience a further broadening and the intensity of the comb lines are fairly equalised. This approach was mathematically modelled by means of a Generalised Nonlinear Schrödinger Equation (GNLS) that contains terms describing the nonlinear optical Kerr effect, the delayed Raman response, the pulse self-steepening, and the linear optical losses as well as the wavelength-dependent Erbium gain profile for the second fibre. The initial condition equation being a deeply-modulated cosine-wave mimics the radiation of the two initial CW lasers. The numerical studies are performed with the help of Matlab scripts that were specifically developed for the integration of the GNLS and the initial condition according to the proposed approach for the OFC generation. The scripts are based on the Fourth-Order Runge-Kutta in the Interaction Picture Method (RK4IP) in combination with the local error method.

This work includes the studies and results on the length optimisation of the first and the second fibre depending on different values of the group-velocity dispersion of the first fibre. Such length optimisation studies are necessary because the OFC have the biggest possible broadband and exhibit a low level of noise exactly at the optimum lengths. Further, the optical pulse build-up in the first and the second fibre was studied by means of the numerical technique called Soliton Radiation Beat Analysis (SRBA). It was shown that a common soliton crystal state is formed in the first fibre for low laser input powers. The soliton crystal continuously dissolves into separated optical solitons as the input power increases. The pulse formation in the second fibre is critically dependent on the features of the pulses formed in the first fibre. I showed that, for low input powers, an adiabatic soliton compression delivering low-noise OFC occurs in the second fibre.  At high input powers, the pulses in the first fibre have more complicated structures which leads to the pulse break-up in the second fibre with a subsequent degradation of the OFC noise performance. The pulse intensity noise studies that were performed within the framework of this thesis allow making statements about the noise performance of an OFC. They showed that the intensity noise of the whole system decreases with the increasing value of LFS.

This article explores the timbre of Thai classical singing with an emphasis on uan, a wordless vocalization based upon specific vowels and consonants, using spectrographic images. Spectrographs are computer images that visualize the fundamental, overtones, and noise-like sounds of a performance. Uan can be reduced to five basic sounds and are analyzed individually and then placed within a musical context. Performances from different generations and musical lineages are contrasted and compared in relation to timbre. I argue it is the relative timbral consistency of the five basic uan sounds, connecting musical generations and lineages, combined with the unique characteristics of each performance that defines the distinct sound of Thai classical singing.

While analyses of vocal music often highlight connections between textual meaning and musical structure, less common is the study of language sounds in relation to musical structure.  This presentation explores Guillaume de Machaut’s virelai Tuit mi penser, highlighting connections that exist between language sounds, pitch space and meaning.  Vowel and consonant content is analyzed in the text, and computer images are used to study the language sounds of an actual performance.  One of my main conclusions is that Tuit mi penser not only displays a cogent pitch space structure, but also projects a vivid sound design created through the language sounds of the text.  The language sounds, pitches, and registers often reinforce one another, working in tandem to convey the imagery and meaning of the text.
.

This paper analyzes the Qin composition Water and Clouds over Xiao Xiang, using a variety of Western theoretical and/or analytical approaches.  Mode, pitch, motive, register, rhythm, timbre, and form are each explored.  Schenkerian influenced linear graphs are used to show motivic and melodic connections, and computer spectrographic images reveal the timbre of specific moments as well as the entire work.  One of the main conclusions is that the form of the work is in a state of constant flux.
.

Physical parameters of the solar chromosphere are determined by observing the flash spectrum of a total solar eclipse. Flash spectrum is a phenomenon that is only visible a few second before and after the totality of a solar eclipse. Specific spectrograph design is needed to suit the purpose of the flash spectrum recordings. A spectrograph has been designed and built to capture the flash spectrum during the total solar eclipse of 2009. The design and construction of the spectrograph is described in this paper. Some emission lines from the solar chromosphere were recorded. The observation was less successful due to some technical problems and weaknesses of the spectrograph. This led to the second design of the spectrograph. The improved version spectrograph covered the spectral range from 4750Å to 6750 Å with dispersion of 1.5 Å/pixel. Chromospheric spectrum was recorded during the annular solar eclipse of 2010.

Following Derrida, in this paper we hope to reinscribe the familiar musi­ cological concepts of analysis and performance, drawing them into new relationships, in order to turn them against their presuppositions and produce new configurations. Through an exploration of analysis, perfor­ mance, and images of musical sound, these new configurations highlight surface details and offer an alternative approach to previous analysis and performance paradigms, leading to a reformulation of the concept of the musical "work." The relationship between analysis and performance has posed challeng­ ing questions for musicologists, theorists, and performers, generating some of the most thought-provoking discussions in the literature. The endeavors of analysis and performance are closely related, yet historically they have em­ ployed different methods and participated in different traditions. Nicholas Cook writes, "I would like to counterpose not so much the analyst and the performer ...

Context. The field of exoplanet research is moving towards the detection and characterization of habitable planets. These exo-Earths can be easily found around low-mass stars by using either photometric transit or radial-velocity (RV) techniques. In the latter case the gain is twofold because the signal induced by the planet of a given mass is higher due to the more favourable planet-star mass ratio and because the habitable zone lies closer to the star. However, late-type stars emit mainly in the infrared (IR) wavelength range, which calls for IR instruments. Aims. SPIRou is a stable RV IR spectrograph addressing these ambitious scientific objectives. As with any other spectrograph, calibration and drift monitoring is fundamental to achieve high precision. However, the IR domain suffers from a lack of suitable reference spectral sources. Our goal was to build, test and finally operate a Fabry-Pérot-based RV-reference module able to provide the needed spectral information over the full wavelength range of SPIRou. Methods. We adapted the existing HARPS Fabry-Pérot calibrator for operation in the IR domain. After manufacturing and assembly, we characterized the FP RV-module in the laboratory before delivering it to the SPIRou integration site. In particular, we measured finesse, transmittance, and spectral flux of the system. Results. The measured finesse value of F = 12.8 corresponds perfectly to the theoretical value. The total transmittance at peak is of the order of 0.5%, mainly limited by fibre-connectors and interfaces. Nevertheless, the provided flux is in line with the the requirements set by the SPIRou instrument. Although we could test the stability of the system, we estimated it by comparing the SPIRou Fabry-Pérot with the already operating HARPS system and demonstrated a stability of better than 1 m s −1 during a night. Conclusions. Once installed on SPIRou, we will test the full spectral characteristics and stability of the RV-reference module. The goal will be to prove that the line position and shape stability of all lines is better than 0.3 m s −1 between two calibration sequences (typically 24 hours), such that the RV-reference module can be used to monitor instrumental drifts. In principle, the system is also intrinsically stable over longer time scales such that it can also be used for calibration purposes.

We describe the new spectroscopic data reduction pipeline for the multi-object MMT/Magellan Infrared Spectrograph. The pipeline is implemented in idl as a stand-alone package and is publicly available in both stable and development versions. We describe novel algorithms for sky subtraction and correction for telluric absorption. We demonstrate that our sky subtraction technique reaches the Poisson limit set by the photon statistics. Our telluric correction uses a hybrid approach by first computing a correction function from an observed stellar spectrum, and then differentially correcting it using a grid of atmosphere transmission models for the target airmass value. The pipeline provides a sufficient level of performance for real time reduction and thus enables data quality control during observations. We reduce an example dataset to demonstrate the high data reduction quality.