Analog Single Sideband-Pulse Width Modulation Processor for Parametric Acoustic Arrays

Parametric acoustic arrays are ultrasonic-based loudspeakers that produce highly directive audio. The audio must first be preprocessed and modulated into an ultrasonic carrier before being emitted into the air, where it will self-demodulate in the far field. The resulting audio wave is proportional to the double time-derivative of the square of the modulation envelope. This thesis presents a fully analog processor which encodes the audio into two Pulse Width Modulated (PWM) signals in quadrature phase and sums them together to produce a Single Sideband (SSB) spectrum around the fundamental frequency of the PWM signals. The two signals are modulated between 8% and 24% duty cycle to maintain a quasi-linear relationship between the duty cycle and the output signal level. This also allows the signals to sum without overlapping each other, maintaining a two-level output. The system drives a network of narrowband transducers with a center frequency equal to the PWM fundamental. Because the transducers are voltage driven, they have a bandpass frequency response which behaves as a first-order integrator on the SSB signal, eliminating the need for two integrators in the processor. Results show that the “SSB-PWM” output wave has a consistent 20-30dB difference in magnitude between the upper sideband and lower sideband. In simulation, a single tone test shows higher total harmonic distortion for lower frequencies and higher modulation depth. A two-tone test creates a 2nd order intermodulation term that increases with the frequencies of the input signals

Virtual acoustics in practice rooms

Musiikin harjoitusluokkien pienestä koosta johtuen akustiikkasuunnittelussa joudutaan usein tekemään kompromisseja jälkikaiunnan ja tarvittavan vaimennusmateriaalin määrän suhteen. Harjoittelua ja instrumentin ääntä tukevaa sointia silmälläpitäen olisi suotavaa, ettei huone olisi kaiunnaltaan täysin kuiva. Kaiuttomassa tilassa soittaminen käy nopeasti raskaaksi ja saattaa vähentää aloittelevien soittajien harjoitteluintoa. Jälkikaiuntaa pieneen tilaan tavoiteltaessa joudutaan perinteisin akustisin menetelmin vähentämään vaimennuksen määrää, mikä puolestaan nostaa tilan äänitasoa. Varsinkin musiikin opettajien pidemmät altistusajat hyvin kaiuntaisissa opetusluokissa saattavat johtaa kuuloon liittyviin ongelmiin. Orkesterien tilanne on usein samankaltainen, kun harjoituksia joudutaan varsinaisen konserttisalin sijasta järjestämään akustisesti sopimattomissa tiloissa. Tässä työssä tutkitaan sähköakustisen järjestelmän käyttöä harjoitustilojen akustiikan parantamiseksi. Tarkoituksena on näin ollen lisätä jälkikaiuntaa nostamatta tilan äänitasoa. Tavoitteena on myös tutkia käyttäjien suhtautumista sähköakustiikan käyttöön. Työssä esitettyjä tutkimuksia varten sähköakustista järjestelmää kokeiltiin yhteensä kolmessa tilassa. Tutkituista tiloista kaksi ensimmäistä olivat tyypillisiä musiikkioppilaitoksen pieniä harjoitus- ja opetusluokkia. Kolmas tila oli monikäyttösali, johon sähköakustiikan avulla pyrittiin luomaan konserttisalin lavaa muistuttava akustiikka sinfoniaorkesterin harjoitusta varten. Tiloissa tehtiin huoneakustisia mittauksia sekä haastateltiin käyttäjiä kyselytutkimuksella. Tutkimusten tulosten perusteella on todettavissa, että harjoitustilojen akustiikan parantaminen sähköakustisella järjestelmällä on mahdollista.Due to their small size, the acoustical design of music practice rooms at music institutes presents designers with challenges and requires compromises between absorption and reverberation. In practice, some reverberation is needed to provide support and more lively sound for the musician. Playing in a room with plenty of absorption and very little reverberation is often uninspiring and easily causes fatigue. On the other hand, increasing reverberation by reducing the absorption results in higher sound pressure levels. As music teachers are exposed to these conditions for long periods of time, in the long term this can lead to hearing problems. Similar problems are often also faced by orchestras when rehearsals are held in facilities with poor acoustical conditions. This work investigates the use of an electro-acoustic system to improve the acoustics in practice spaces. The electro-acoustic system uses an active method to create additional reverberation without increasing the sound pressure levels. A second objective is to evaluate the acceptance of virtual acoustics by users in music practice spaces. For this purpose, a prototype of an electro-acoustic system was installed in three different rooms, and the reverberation time and sound pressure level of the rooms were measured. These case studies consist of two small classrooms and a theater hall converted to a rehearsal hall for a symphony orchestra. For each case study, subjective opinions were collected. The results for each room were then analyzed in terms of the feedback from the users. The case studies show that with a careful tuning, and especially in larger spaces, a virtual acoustic system is a potential solution for improving the room acoustics of a practice room

Applied Signal Processing

Being an inter-disciplinary subject, Signal Processing has application in almost all scientific fields. Applied Signal Processing tries to link between the analog and digital signal processing domains. Since the digital signal processing techniques have evolved from its analog counterpart, this book begins by explaining the fundamental concepts in analog signal processing and then progresses towards the digital signal processing. This will help the reader to gain a general overview of the whole subject and establish links between the various fundamental concepts. While the focus of this book is on the fundamentals of signal processing, the understanding of these topics greatly enhances the confident use as well as further development of the design and analysis of digital systems for various engineering and medical applications. Applied Signal Processing also prepares readers to further their knowledge in advanced topics within the field of signal processing

NASA Thesaurus. Volume 2: Access vocabulary

The NASA Thesaurus -- Volume 2, Access Vocabulary -- contains an alphabetical listing of all Thesaurus terms (postable and nonpostable) and permutations of all multiword and pseudo-multiword terms. Also included are Other Words (non-Thesaurus terms) consisting of abbreviations, chemical symbols, etc. The permutations and Other Words provide 'access' to the appropriate postable entries in the Thesaurus

NASA thesaurus. Volume 2: Access vocabulary

The Access Vocabulary, which is essentially a permuted index, provides access to any word or number in authorized postable and nonpostable terms. Additional entries include postable and nonpostable terms, other word entries, and pseudo-multiword terms that are permutations of words that contain words within words. The Access Vocabulary contains 40,738 entries that give increased access to the hierarchies in Volume 1 - Hierarchical Listing

NASA Thesaurus. Volume 1: Hierarchical listing

There are 16,713 postable terms and 3,716 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary

NASA thesaurus. Volume 1: Hierarchical Listing

There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions

The investigation and design of a piezoelectric active vibration control system for vertical machining centres

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Proceedings of the 7th Sound and Music Computing Conference

Proceedings of the SMC2010 - 7th Sound and Music Computing Conference, July 21st - July 24th 2010