David H. Griesinger

Quantifying musical acoustics through audibility

This paper proposes a set of measures of musical acoustics derived from a study of binaural hearing and speech perception. The measures are tested on analyzing data from unoccupied and occupied halls, data from several halls which include electronically variable acoustics capable of a wide range of adjustment, and data from a binaural synthesizer of hall acoustics. The new measures include the 500‐ms reverberant level (L500), early (0–60 ms) reverb time (ERT), middle (0.1–0.5 s) reverb time (MRT), late (0.5+) reverb time (LRT), early binaural fraction (EBF), and middle binaural fraction (MBF). L500, a measure of reverberant level, is related to early decay time (EDT). Optimum L500 is found to be high in the range of musical fundamentals, and low in the region of maximum speech information. ERT is in part a measure of the localizability of the sound, which is related to its clarity. MRT is particularly significant whenever the decay curve is not a simple exponential. It is found that when MRT is much longe...

The audibility of direct sound as a key to measuring the clarity of speech and music

Human ear/brain systems evolved to decode the direction, timbre, and distance of multiple sounds in a complex and noisy environment. In a reverberant space, this information is only available at the onset of a sound, before reflections overwhelm it. But since the time of Sabine acoustic science has concentrated on the decay of sound in a reverberant field, not on the audibility of the onset information. In addition, it is well known that the ability to separate multiple sound sources depends critically on pitch, but acoustic research studies only noise and impulses. This paper proposes that clarity requires the ability to separately analyze multiple sounds (the cocktail party effect) and that the cocktail party effect depends on phase relationships between harmonics of complex tones. These phase relationships are scrambled in predicable ways by reflections and reverberation. Well known properties of human hearing are used to develop both a physical model for the neurology of onset detection and an impulse...

What is "clarity", and how it can be measured?

Human hearing did not evolve to detect reflections and reverberation. It is the ability to detect the direct component of a sound field that allows us to separate simultaneous signals, determine their direction, their timbre, their distance, and their importance for our attention. “Clarity” is perceived when we can separately detect direct sound. But ISO3382 measures concentrate on reflections, and are either blind to the direct component of a sound field or misinterpret its significance. They fail to predict sound quality in individual seats. We will demonstrate the vital importance of clarity through demonstrations of “clear” and “muddy” in speech and music. We will then present three physiologically based methods that measure the degree of clarity in a particular acoustic environment. The first, LOC, uses a simple nerve firing model to analyze an impulse response for the build-up of reflected energy at the onsets of sounds. The second method measures the degree of phase randomization above 1000 Hz caus...

Listening to the acoustics in concert halls

How does acoustics affect the symphonic music performed in a concert hall? The lecture begins with an illustrated discussion of the architectural features that influence the acoustics. Boston Symphony Hall, which was built in 1900 when only one facet of architectural design was known, now rates as one of the world’s great halls. How this occurred will be presented. Music is composed with some acoustical environment in mind and this varies with time from the Baroque to the Romantic to the Modern musical period. Conductors vary their interpretation according to the hall they are in. Well‐traveled listeners and music critics have favorite halls. The lecture then presents a list of 58 halls rank ordered according to their acoustical quality based on interviews of music critics and conductors. Modern acoustical measurements made in these halls are compared with their rankings. Music recordings will be presented that demonstrate how halls sound that have different measured acoustical parameters. Photographs of a number of recently built halls are shown as examples of how these known acoustical factors have been incorporated into architectural design.

Recent experiences with electronic acoustical enhancement in concert halls, opera houses, and outdoor venues

This paper gives a brief summary of acoustical theory based on human perception. It then uses this theory to discuss the design criteria and performance data of electronic acoustic‐enhancement systems installed in a number of venues. The installations include the Deutches Staatsoper in Berlin, the Hummingbird Centre in Toronto, the Circle Theatre in Indianapolis, the Adelaide Festival Centre Theater in Adelaide, Australia, and Morbisch FestSpiele in Austria. Solutions to the problems of maintaining optimum clarity while providing optimum envelopment are given.

Preference, localization, attention, and the limit of localization distance (LLD)

Recent work by Lokki et al. has found that a perception he calls “proximity” is a major component of preference in concert halls. In this talk we propose that proximity is perceived when sources are close enough or clear enough that they can be sharply localized and understood. In halls and rooms we find this ability abruptly disappears at a critical distance from the source, the Limit of Localization Distance, or LLD. We find that proximity attracts and holds attention, which is a major reason cinemas and drama theaters have dry acoustics and strong direct sound paths. In this talk we will describe the physics behind the perception of proximity, why it has not been previously recognized, how to predict where the LLD will occur from a binaural impulse response, and how to optimize proximity in halls, theaters, and classrooms.Recent work by Lokki et al. has found that a perception he calls “proximity” is a major component of preference in concert halls. In this talk we propose that proximity is perceived when sources are close enough or clear enough that they can be sharply localized and understood. In halls and rooms we find this ability abruptly disappears at a critical distance from the source, the Limit of Localization Distance, or LLD. We find that proximity attracts and holds attention, which is a major reason cinemas and drama theaters have dry acoustics and strong direct sound paths. In this talk we will describe the physics behind the perception of proximity, why it has not been previously recognized, how to predict where the LLD will occur from a binaural impulse response, and how to optimize proximity in halls, theaters, and classrooms.

Where not to install a reverberation enhancement system

For hundreds (perhaps thousands) of years venues for live performance emphasized communication—the transfer of speech or musical information from performers to listeners—as paramount to success. The Greeks could perform drama to 15,000 listeners without microphones, and halls used by Haydn, Mozart, and Beethoven were small and dry. Wagner built a fan-shaped opera hall with an absorbent stage, a covered pit, and no lateral reflections. It is still considered perhaps the best in the world. Sabine and others made lecture and Vaudeville halls that worked. But in the 20th century suddenly early reflections were essential, and long reverberation times desirable. Wood stages and lateral reflections were mandatory. These ideas linger on. In this talk we share our experiences of often misguided attempts to improve sound in venues of all types. The lessons we learned from a few perceptive musicians and artists have changed our approach to acoustics. Attention is the key, not reverberation. Reverberation can be love...

The importance of phase, attention, intelligibility, and recall in sound system design

Measures for the accuracy of speech transmission over an audio channel, such as Speech Transmission Index, rely on random word recognition as the standard for quality. In this paper, we propose that the ability to recall information at a later time is a more useful standard for sound quality than simply recognizing words. Recall, particularly in a complex or noisy environment, depends critically on the focused attention of a listener. There is evidence that “proximity,” the auditory perception that a source is close to a listener, enhances both focused attention and the ability to localize and separate sound sources from competing signals. We find that proximity and the benefits it brings depend on the phase alignment of frequencies above 1000 Hz. This alignment is lost when there are excess reflections, reverberation, noise, or multiple loudspeakers. We will present measurement techniques that can quantify proximity from an impulse response, and sound designs that maximize it in practice.

The physics of auditory proximity: Auditory mechanisms that extract pitched signals from noise and other signals

Cutthroat evolution has given us seemingly magical abilities to hear speech in complex environments. For example, we can tell instantly, independent of timbre or loudness, if a sound is close to us. In a crowded room, we can switch attention at will between at least three different simultaneous conversations, and involuntarily switch to one of them if our name is spoken. These feats are only possible if, without conscious attention, each voice has been separated into an independent neural stream. The separation process relies on the phase relationships between the harmonics above 1000 Hz that encode speech information, and the neurology of the inner ear that has evolved to detect them. When phase is undisturbed, once in each fundamental period harmonic phases align to create massive peaks in the sound pressure at the fundamental frequency. Pitch-sensitive filters can detect and separate these peaks from each other and from noise with amazing acuity. But reflections and sound systems randomize phases, with...

Beyond ISO3382—Measuring acoustics with live sound

Current acoustic measurements techniques typically require time and heavy equipment. The effort and expense would be justified if the results accurately predicted the sound quality from a performance at an individual seat, but they do not. If one believes that it is possible to hear and accurately report sound quality from live sound in different seats, then it must be possible to measure it this way. This paper describes a model of human hearing that promises to provide this ability, at least for quality aspects relating to clarity. The model is based on the ease with which information is carried from one or more sources to a listener. For speech, this involves both reverberant masking from late reverberation, and interference to the direct sound from early reflections. To make such a measurement, we need to model how the ear and brain system precisely localizes sound sources, and separates their sound from each other and acoustic interference without added information from context, grammar, or prior kno...