1. Terminal – Shepard scale 

The Shepard tone or Shepard scale, introduced in 1964 by psychologist Roger Shepard, is the illusion of an infinitely ascending or descending scale that never transcends the boundaries of one’s own hearing. This effect is achieved by arranging sounds with a partial tonal structure in octaves under a bell- shaped filter curve. This means that the partials are always strongest in the middle and always weakest at the upper and lower margins. In other words, the scale seems to keep going up or down without disappearing completely below the upper or lower hearing threshold. 

2. Terminal – Hearing in the womb 

The ear is one of the earliest functioning sensory organs of a developing human being, even before the heart and brain are active. As early as between week 20 and 24, an auditory stimulus can initiate movement in the fetus. From week 28 onwards, one can presuppose the ability to hear in a healthy fetus. It perceives signals and sound through its skin, the air, and the bones. It can hear the heart beat and voice of the mother, as well as the digestive sounds and stomach rumbling. Conversations, music, ambient sound are received through a filter. Predominantly, it is the darker tones that penetrate. Vowels tend to be perceived as consonants, which is why the fetus primarily hears the speech melody and less of the percussive elements of spoken content. 

3. Terminal – Waveform 

Waveform is the visual representation of varying amplitudes of an oscillation over time. The four basic periodic waveforms are sine, square, triangle and sawtooth. In acoustics, the term „waveform“ refers to the envelope of acoustic oscillations in an oscillogram of graphical user interfaces. 

With a filter, an audio signal’s phase and amplitude can be changed depending on the chosen frequency. The cutoff parameter is used, for example, to reduce or cancel out unwanted signal components. The set cutoff frequency can also be augmented with the resonance parameter. 

An LFO (Low Frequency Oscillator) is used to modulate a sound parameter both permanently and rhythmically according to a recurring pattern (depending on the set waveform). An LFO creates movement in the sound, making it more lively and literally more vibrant. It makes sounds “breathe,” “shimmer” or “pulsate”. 

4. Terminal – Threshold of hearing 

The human ear can perceive frequencies ranging from about 16 to 18000 Hz. The lower the frequency, the lower the sound; the higher the frequency, the higher the sound. However, the limits of our hearing are very individual. The older we get, the more our ability to hear higher frequencies decreases (Statistically, we lose about 1000 Hz every ten years). Often, hearing is also impaired by consuming music at high volumes, regardless of the genre. High frequencies are mostly affected because their receptors are located at the beginning of the cochlea. If these fine sensory cells are damaged, certain acoustic signals are no longer transmitted to the brain. 

5. Terminal – Ambient Sound

How music sounds is influenced greatly by the room or space in which it is played. The main reasons for this are the phenomena of sound reflection and absorption. Depending on the size of the space and the nature of the surrounding surfaces, sound waves are reflected with varying intensity. Sound propagates spherically in the form of a sound wave and hits surfaces that partly reflect and absorb it. In general, smooth surfaces generate strong reflections, while uneven surfaces reduce reflection – particularly concerning the higher frequencies. In room acoustics, sound waves are often described as sound rays that are reflected back at the same angle upon impact, just like light is. 

This way, one can systematically target sound through reflection (e.g. by avoiding echoes). Propagation and reflection both reduce the energy of sound, which is converted into heat. The shortest possible path from sound source to listener is called “direct sound”. Soon after, the sound waves reflected from walls and ceilings arrive, which are called first/ early reflections. They are succeeded by a proliferating number of different reflections, whose amplitudes decrease continually and are perceived as a gradually fading “reverberation”. 

6. Terminal – The world of Sound for Animals

Human sound perception differs greatly from an animals percieved world of sound. We can make assumptions about how the spoken word and music are received by other human beings, but how is it with animals? Can a turtle hear us talk? What does a fish hear in the aquarium? Would a bat appreciate Chopin’s piano concertos? Is pop music torture to a cat’s ears? For a project that was started at the institute of Research in Music Education at the Hannover University of Music, Drama and Media in 2002, a team under the supervision of Prof. Dr. Reinhard Kopiez began researching these questions.

The aim was to create audiograms for selected species through methods of digital signal processing. The foundation of this project was the vast data collection found in Richard R. Fay’s (1988): “Hearing in vertebrates: A psychophysics databook”, Winnetka, IL: Hill-Fay Associates. This book is presumably the biggest data collection concerning vertebrates’ hearing capacities and the collected data, gathered through animal behavioral experiments, can tell us about the hearing threshold of particular species or the resolution of their directional hearing. 

But how does a carp hear a Beethoven Symphony under water? One can only take a wild guess. If animals are capable of recieving sound in the same way humans do cannot be absolutely verified, but from Fay’s audiograms we can conclude specific information about each animal’s perceivable frequency spectrum. This is what Kopiez and his team managed to make audible and comprehensible with their experiments.