Acoustics of the banjo: measurements and sound synthesis

Measurements of vibrational response of an American 5-string banjo and of the sounds of played notes on the instrument are presented, and contrasted with corresponding results for a steel-string guitar. A synthesis model, fine-tuned using information from the measurements, has been used to investigate what acoustical features are necessary to produce recognisable banjo-like sound, and to explore the perceptual salience of a wide range of design modifications. Recognisable banjo sound seems to depend on the pattern of decay rates of “string modes”, the loudness magnitude and profile, and a transient contribution to each played note from the “body modes”. A formant-like feature, peaking around 500–800 Hz on the banjo tested, is found to play a key role. At higher frequencies the dynamic behaviour of the bridge produces additional formant-like features, reminiscent of the “bridge hill” of the violin, and these also produce clear perceptual effects

Perception of attributes in real and synthetic string instrument sounds

This thesis explores the perceptual features of natural and synthetic string instrument sounds. The contributions are in formal listening experiments on a variety of features in musical sounds that have not been studied in detail previously. The effects of inharmonicity on timbre and pitch have been measured. The results indicate that the implementation of inharmonicity is not always necessary. The timbre effect is more salient in natural instruments, but for high tones a pitch difference may also be detected. Guidelines were given for compensation of the pitch effect. A perceptual study of the decaying parameters showed that large deviations from the reference value are tolerated perceptually. The studies on the audibility of initial pitch glides and dual-polarization effects provides practical knowledge that helps in the implementation of these features in digital sound synthesis. Related to expression rather than basic string behavior, the study on perception-based control of the vibrato parameters has a sligthly different background. However, all of the studied features are more or less player-controlled by different ways of plucking the string or pressing the key. The main objective of the thesis is to find answers to current problems in digital sound synthesis, such as parameter quantization. Another aim is to gain more general understanding of how we perceive musical sounds.reviewe

Automatic Transcription of Bass Guitar Tracks applied for Music Genre Classification and Sound Synthesis

Musiksignale bestehen in der Regel aus einer Überlagerung mehrerer Einzelinstrumente. Die meisten existierenden Algorithmen zur automatischen Transkription und Analyse von Musikaufnahmen im Forschungsfeld des Music Information Retrieval (MIR) versuchen, semantische Information direkt aus diesen gemischten Signalen zu extrahieren. In den letzten Jahren wurde häufig beobachtet, dass die Leistungsfähigkeit dieser Algorithmen durch die Signalüberlagerungen und den daraus resultierenden Informationsverlust generell limitiert ist. Ein möglicher Lösungsansatz besteht darin, mittels Verfahren der Quellentrennung die beteiligten Instrumente vor der Analyse klanglich zu isolieren. Die Leistungsfähigkeit dieser Algorithmen ist zum aktuellen Stand der Technik jedoch nicht immer ausreichend, um eine sehr gute Trennung der Einzelquellen zu ermöglichen. In dieser Arbeit werden daher ausschließlich isolierte Instrumentalaufnahmen untersucht, die klanglich nicht von anderen Instrumenten überlagert sind. Exemplarisch werden anhand der elektrischen Bassgitarre auf die Klangerzeugung dieses Instrumentes hin spezialisierte Analyse- und Klangsynthesealgorithmen entwickelt und evaluiert.Im ersten Teil der vorliegenden Arbeit wird ein Algorithmus vorgestellt, der eine automatische Transkription von Bassgitarrenaufnahmen durchführt. Dabei wird das Audiosignal durch verschiedene Klangereignisse beschrieben, welche den gespielten Noten auf dem Instrument entsprechen. Neben den üblichen Notenparametern Anfang, Dauer, Lautstärke und Tonhöhe werden dabei auch instrumentenspezifische Parameter wie die verwendeten Spieltechniken sowie die Saiten- und Bundlage auf dem Instrument automatisch extrahiert. Evaluationsexperimente anhand zweier neu erstellter Audiodatensätze belegen, dass der vorgestellte Transkriptionsalgorithmus auf einem Datensatz von realistischen Bassgitarrenaufnahmen eine höhere Erkennungsgenauigkeit erreichen kann als drei existierende Algorithmen aus dem Stand der Technik. Die Schätzung der instrumentenspezifischen Parameter kann insbesondere für isolierte Einzelnoten mit einer hohen Güte durchgeführt werden.Im zweiten Teil der Arbeit wird untersucht, wie aus einer Notendarstellung typischer sich wieder- holender Basslinien auf das Musikgenre geschlossen werden kann. Dabei werden Audiomerkmale extrahiert, welche verschiedene tonale, rhythmische, und strukturelle Eigenschaften von Basslinien quantitativ beschreiben. Mit Hilfe eines neu erstellten Datensatzes von 520 typischen Basslinien aus 13 verschiedenen Musikgenres wurden drei verschiedene Ansätze für die automatische Genreklassifikation verglichen. Dabei zeigte sich, dass mit Hilfe eines regelbasierten Klassifikationsverfahrens nur Anhand der Analyse der Basslinie eines Musikstückes bereits eine mittlere Erkennungsrate von 64,8 % erreicht werden konnte.Die Re-synthese der originalen Bassspuren basierend auf den extrahierten Notenparametern wird im dritten Teil der Arbeit untersucht. Dabei wird ein neuer Audiosynthesealgorithmus vorgestellt, der basierend auf dem Prinzip des Physical Modeling verschiedene Aspekte der für die Bassgitarre charakteristische Klangerzeugung wie Saitenanregung, Dämpfung, Kollision zwischen Saite und Bund sowie dem Tonabnehmerverhalten nachbildet. Weiterhin wird ein parametrischerAudiokodierungsansatz diskutiert, der es erlaubt, Bassgitarrenspuren nur anhand der ermittel- ten notenweisen Parameter zu übertragen um sie auf Dekoderseite wieder zu resynthetisieren. Die Ergebnisse mehrerer Hötest belegen, dass der vorgeschlagene Synthesealgorithmus eine Re- Synthese von Bassgitarrenaufnahmen mit einer besseren Klangqualität ermöglicht als die Übertragung der Audiodaten mit existierenden Audiokodierungsverfahren, die auf sehr geringe Bitraten ein gestellt sind.Music recordings most often consist of multiple instrument signals, which overlap in time and frequency. In the field of Music Information Retrieval (MIR), existing algorithms for the automatic transcription and analysis of music recordings aim to extract semantic information from mixed audio signals. In the last years, it was frequently observed that the algorithm performance is limited due to the signal interference and the resulting loss of information. One common approach to solve this problem is to first apply source separation algorithms to isolate the present musical instrument signals before analyzing them individually. The performance of source separation algorithms strongly depends on the number of instruments as well as on the amount of spectral overlap.In this thesis, isolated instrumental tracks are analyzed in order to circumvent the challenges of source separation. Instead, the focus is on the development of instrument-centered signal processing algorithms for music transcription, musical analysis, as well as sound synthesis. The electric bass guitar is chosen as an example instrument. Its sound production principles are closely investigated and considered in the algorithmic design.In the first part of this thesis, an automatic music transcription algorithm for electric bass guitar recordings will be presented. The audio signal is interpreted as a sequence of sound events, which are described by various parameters. In addition to the conventionally used score-level parameters note onset, duration, loudness, and pitch, instrument-specific parameters such as the applied instrument playing techniques and the geometric position on the instrument fretboard will be extracted. Different evaluation experiments confirmed that the proposed transcription algorithm outperformed three state-of-the-art bass transcription algorithms for the transcription of realistic bass guitar recordings. The estimation of the instrument-level parameters works with high accuracy, in particular for isolated note samples.In the second part of the thesis, it will be investigated, whether the sole analysis of the bassline of a music piece allows to automatically classify its music genre. Different score-based audio features will be proposed that allow to quantify tonal, rhythmic, and structural properties of basslines. Based on a novel data set of 520 bassline transcriptions from 13 different music genres, three approaches for music genre classification were compared. A rule-based classification system could achieve a mean class accuracy of 64.8 % by only taking features into account that were extracted from the bassline of a music piece.The re-synthesis of a bass guitar recordings using the previously extracted note parameters will be studied in the third part of this thesis. Based on the physical modeling of string instruments, a novel sound synthesis algorithm tailored to the electric bass guitar will be presented. The algorithm mimics different aspects of the instrument’s sound production mechanism such as string excitement, string damping, string-fret collision, and the influence of the electro-magnetic pickup. Furthermore, a parametric audio coding approach will be discussed that allows to encode and transmit bass guitar tracks with a significantly smaller bit rate than conventional audio coding algorithms do. The results of different listening tests confirmed that a higher perceptual quality can be achieved if the original bass guitar recordings are encoded and re-synthesized using the proposed parametric audio codec instead of being encoded using conventional audio codecs at very low bit rate settings

Timbre perception of cochlear implant users

The timbre perception of cochlear implantees (CI) is poor compared to normal hearing (NH) listeners. The cues that are normally transmitted to NH listeners may be less salient or even absent for CI users. From the literature, two spectral (brightness (Tb) and irregularity (IRR)) and two temporal timbre parameters (log rise-time (LRT) and sustain/decay (S/D) parameter (n)) have been identified as important timbre parameters. Each of these parameters was extracted for a set of thirteen instruments. Sounds could be resynthesized according to the specific timbre parameter set. The variation of loudness, pitch and perceived duration as functions of the timbre parameters were investigated to provide systematic balancing methods. The just-noticeable differences (JNDs) were obtained for each of the parameters for thirteen instruments for NH listeners and a reduced instrument set of nine instruments for the CI users using a 1-up, 2-down, two-alternative, forced choice procedure. From the JNDs, predicted confusion matrices were constructed. From the confusion matrices, a feature information transmission analysis (FITA) indicated the salience of each of the parameters and NH and CI results could be compared.Dissertation (MEng)--University of Pretoria, 2011.Electrical, Electronic and Computer EngineeringMEngUnrestricte

Impulsive sound quality of tennis rackets

The sound radiated during a tennis impact has been shown to greatly influence the perception of ‘feel’ but has also been suggested to contribute to the perception of equipment quality, as is the case with many other consumer products. In an industry that is governed by design limitations, tennis racket manufactures are continually aiming to differentiate their products from their competitors’ and the sound character of a racket is seen as one such method to do so. In order to control the sound radiated from a tennis racket it was first necessary to identify how a tennis racket radiates sound. Through a number of controlled player tests, involving groundstrokes and serves, the sound was recorded along with measurements of the physical vibrations excited in the frame. Analysis of the data revealed typical characteristics of the sound in the time and frequency domain. The sound was split into two sections to aid the analysis; an initial impulsive component that decayed very quickly and a ringing component that was of much lower amplitude but decayed at a much slower rate. The evolution of the frequency content over time was also investigated, however, the data provided much more information as to where each frequency component originated by analysing the data together with the experimental modal analysis data. The experimental modal analysis of a tennis racket was a vital stage in understanding which components of the racket were responsible for radiating the identified frequency component in the sound spectrum. The investigations identified frame bending modes, out-of-plane and inplane, as well as torsional modes, hoop modes and stringbed modes. To enable direct comparison between the natural frequencies excited during a tennis shot and the frequencies recorded from a freely suspended racket, the effect of the hand on the modal behaviour of the racket was analysed; experimental modal analysis data from a hand-gripped racket was compared with data generated by adding simulated mass to the modal model of the freely suspended racket. The first stringbed mode was identified as a key contributor to the sound of the racket, especially in the ringing component of the sound. Analysis of the physical vibrations in the frame following a tennis shot revealed that the first stringbed mode excited the frame of the racket, which is iv thought to be the reason why stringbed modes contribute to the sound more so than their surface area would suggest that they are capable of. Analysis of the relationship between subjective perceptions of players and calculated sound metrics suggest a negative correlation exists between the duration and loudness of a tennis shot and the appeal of the sound. Further investigations involving a jury to evaluate the appeal of a tennis impact sound, modified in terms of duration, revealed further evidence to support the theory that tennis impact sounds of greater duration are less appealing than those that decay quickly. This is the first study to investigate the sound radiated from a tennis racket and has identified how the sound is radiated from the racket and also suggests which parameters of the sound are considered appealing to tennis players. With this information it is possible to suggest design modifications that would influence the sound of a tennis racket in a predictable manner

Modelling body vibration and sound radiation of a modified kantele

Tässä työssä mallinnetaan 15-kielisen kanteleen kopan värähtelyä ja säteilyä elementtimenetelmän avulla. Kahta perinteistä kopan rakennetta, laatikkokanteletta ja lautakanteletta, verrataan muunneltuun rakenteeseen, jossa kopan ja kannen välillä on ilmarako. Tämä rakenne, jota kutsutaan myös nimellä vapaareuna-erillispohjarakenne, mahdollistaa kannen vapaan värähtelyn. Lisäksi pohjan ja kannen sulkemalla ilmatilalla on omat värähtelymuotonsa. Tämä muunnellun kanteleen on osoitettu olevan äänekkäämpi kuin perinteiset kanteleet. Tässä työssä osoitetaan, että muunnellussa kanteleessa yhdistyvät sekä kannen että ilmatilan värähtelymuodot. Siksi muunnellulla kanteleella on suurempi värähtelymuototiheys kuin perinteisillä kanteleilla. Muunneltu kantele on myös ympärisäteilevämpi, sillä ilmatilan värähtelymuodot kytkeytyvät kopan värähtelyihin. Tästä seuraa, että muunnellun kanteleen säteilytehokkuus on suurempi, kun ilmarako on pieni (1-3 mm).In this thesis, the vibrational modes and radiation of the body of a 15-string instrument called the kantele are modeled using the finite element method. Two traditional body structures, the top-plate kantele and the box kantele, are compared to a modified kantele with an air gap separating the top and the back plate. The modified structure allows the kantele top plate to vibrate freely. In addition, together the top and back plate create an enclosed air mass that has its own vibrational modes. The modified kantele has previously been shown to be louder than the traditional top plate kantele. In this thesis, it is shown that the modified kantele includes vibrational modes of both the freely vibrating top plate and the enclosed air. Thus, it has a higher mode density than the traditional kanteles. Because of the coupling of the enclosed air modes to the body, the modified kantele radiates more omni-directionally than the traditional kanteles. Consequently, the modified kantele has a higher radiation efficiency than the traditional kanteles when the size of the air gap is small (1-3 mm)