Communication Acoustics

In this engineering course, we will cover all aspects of communication acoustics, which is the way sounds travels from a source, through a channel and finally to a receiver. We will look at the different system components involved in acoustic communication, including those between humans, between humans and machines, and between machines. This includes:

• speech acoustics
• hearing acoustics
• electroacoustics
• spatial sound capture and presentation
• simulation of acoustical environments
• the human auditory system
• digital audio processing methods

You will learn from top experts in the field of communication acoustics, who are all affiliated with TU9, the nine leading Universities of Technology in Germany. Together, they have pooled their expertise in order to teach a comprehensive basic understanding and indicate current research trends to you.

After completion of the course, you will have gained a broad understanding of the involved subdomains, and will be ready to pick a specialization for future in-depth study.

Fundamentals of Acoustics (Müller, Vorländer)
You will learn about the physical fundamentals of sound in this session. After the definition of sound, a brief excursion into the perception of sound and its dependence on the frequency is performed followed by an introduction to the logarithmic scale and working with sound pressure levels. The physical basis for sound in air and the mathematical formulation of the governing differential equations are illustrated via audiovisual demonstrations. Further topics are principles of sound generation, propagation and interaction with boundaries as well as radiation of sound using models based on volume sources and the specific far-field and near-field characteristics. Application of the theory is illustrated using the example of a violin.

Fundamentals of Signals and Systems (Ahrens)
This session starts with a recapitulation of the most important principles in the system theory of time-continuous and time-discrete signals such as linearity, time invariance, the Fourier transform, sampling, and aliasing. You will get insights into the conceptual structure of digital signal processing systems and learn about different flavors of convolution, one of the most important mathematical operations in digital audio signal processing. The session concludes with a short introduction to nonlinear systems.

Anatomy and Physiology of the Hearing System (Fels)
You will learn about the peripheral auditory system and about how closely the fundamental spatial hearing mechanisms are tied to the fact that we are listening with two ears. Besides these fundamentals of binaural hearing, the concepts of head-related transfer functions and binaural synthesis are introduced. Finally, the fundamentals of binaural reproduction are presented.

Psychoacoustics (Seeber)
Psychoacoustics connects the physical world of sound with how we perceive it. Auditory perception is studied in listening experiments and the knowledge is used to develop computational models of hearing which are used to, e.g., evaluate virtual acoustics techniques, to optimize sound quality of products, and to improve hearing aids and cochlear implants. You will learn about the range of sounds humans can hear, under which conditions one sound can mask another, how the auditory system processes sounds in frequency bands, how good we are at interpreting spectral and temporal information, and how binaural information can be used to improve hearing in noisy situations. Example listening experiments will help you understand how we gained our knowledge about the hearing system and how it is possible to objectively describe perception.

Electroacoustics (Altinsoy)
This session gives an overview of the domain of electroacoustics, which is one of the fascinating and challenging fields of engineering. You will explore the world of loudspeakers and microphones. Electromechanical and electroacoustical analogies help us understanding the basics, which prepare us for understanding the different transducer technologies. Finally, recent advances in the field such as sound beams or new loudspeaker driver designs will be outlined.

Speech Acoustics (Möller)
You will learn about how human speech is produced, which characteristics of the speech signal result from this production process, and how the production process can be modeled. Furthermore, an overview of the most important techniques for speech signal analysis is given, which base heavily on the acoustic properties of speech presented in the first half of the session.

Sound Recording and Reproduction (Weinzierl)
Almost all productions of music and speech distributed on records, by radio and television or through the internet are designated for stereophonic recording and reproduction. IN this chapter, you will be introduced to the psychoacoustics of stereophonic signals (part I), the most common techniques for stereophonic recording, and the most common formats for reproduction (part II). More recent technologies mark a transition from channel-based to object-based audio transmission, which will also be outlined.

Virtual acoustics I: Binaural Technology (Weinzierl)
Binaural technology is a powerful tool for the simulation of virtual acoustic environments. You will learn how systems for static (part I) and dynamic (part II) binaural synthesis work, and what requirements have to be met with respect to the recording, the spatial resolution, the latency and the equalization of binaural simulations, and to what extent these simulations can provide an authentic reconstruction of real sound fields.

Virtual acoustics II: Sound Field Analysis and Synthesis (Ahrens)
You will learn about the capabilities of microphone arrays and loudspeaker arrays to capture and present spatial sound information. On the capture side, delay-and-sum beamforming is introduced as a simple means for creating electronically steerable directivities. The concept of numerical optimization is briefly outlined in order to introduce the concept of superdirective beamforming. You will then learn about coincident and spherical microphone arrays for the capture of the spatial structure of sound fields. On the spatial presentation side, traditional Ambisonics is presented along with Wave Field Synthesis, higher order Ambisonics, and Directional Audio Coding.

Room Acoustics (Müller)
The sound field in the acoustic cavity and its frequency-dependent characteristics are in the focus of this session. Sound propagation in the open space is discussed as well as when reflecting walls and ceilings are present. You will be able to evaluate impulse response functions regarding direct sound and reflections. After assessing the acoustic properties of a room using specific criteria for speech and music, the sound field can be designed using the phenomena of reflection and absorption. In a journey through history, we will discuss the relevant acoustic effects and methods for room acoustical design at the basis of practical examples of different concert halls.

Room Simulation (Vorländer)
Computer models are powerful tools for simulation of room acoustics. In the first lecture, the principles of room sound fields, the time-domain and frequency-domain representations are introduced with regard to linear and time-invariant system theory. The main methodology for room acoustical simulation - geometrical acoustics - is presented in two algorithms, the image source model and the ray tracing model. Hybrid models pave the way to interfacing the simulations with audio signal processing, to realtime 3D audio and finally to the Virtual Reality technology. All those features of modern room simulation are introduced with a large number of audiovisual demonstrations.

Application: Automatic Speech Recognition and Text-to-Speech Synthesis (Möller)
This session is composed of two parts. Both of them deal with speech as a medium for interaction between humans and computers. The first part provides an overview of the mechanisms to automatically recognize speech using statistical processes such as hidden Markov models or neural networks. The second part deals with the inverse problem, which is making the computer speak. Both techniques make use of the bases of speech production introduced in the Session “Speech Acoustics” of this course.

Product Sound Design (Altinsoy)
In this chapter, you will learn the methodologies of product sound design. It starts from the Gestalt principles and finds its way through the principles of sound synthesis. A short overview of the design process and the cultural aspects will be given.
 
Application of Psychoacoustics in Product Development + Application: Perceptual Audio Coding (Altinsoy, Ahrens)
This session is composed of two independent topics. The first part will be on the application of psychoacoustics in product development. Although sound power or sound pressure level are important acoustical parameters, they do not characterize the customers' perception of product sound sufficiently. The psychoacoustical parameters such as loudness, sharpness, tonality, roughness, fluctuation strength and the like are much more useful for characterization purposes. Case studies from the various industrial areas will deliver an overview. Additionally, psychoacoustical approaches for evaluation of noise immission and soundscapes will be discussed. Finally, the combined influence of auditory, visual, and tactile information on product quality perception will be discussed.
In the part on perceptual audio coding, you will learn about the audio data compression technology that became known under the term MP3. The concept of amplitude quantization and the resulting quantization noise are introduced as the fundamental mechanisms that determine the data volume that is required for the representation of time-discrete audio signals. The relevant psychoacoustic mechanisms are briefly revisited in order to motivate the perceptual encoding strategy, which you will learn about in detail.