Psychoacoustics

Psychoacoustics is the study of how we hear and understand sound. It looks at how our minds and ears work together to process noises like music, speech, and even unwanted sounds such as noise. This field combines many areas of science, including psychology, physics, biology, and engineering.

By studying psychoacoustics, scientists can learn how people perceive different sounds and why some sounds are more pleasant or disturbing than others. This knowledge helps in creating better audio technology, such as headphones and speakers, and in designing environments that are comfortable for listening.

Psychoacoustics also plays a role in understanding how we recognize speech and music, which is important for technologies like voice assistants and music streaming services. It helps explain why certain sounds can affect our mood and how we can use sound to improve communication and design.

Background

Hearing is not just about sound waves moving through the air. When we hear something, the sound travels to our ears and changes into signals that our brain can understand. This means that when we study sound, we need to think about how our ears and brain work together, not just the physics of sound.

Our inner ear does a lot of work to change sound waves into signals for the brain. This helps explain why some sounds feel the same to us, even if they are slightly different. Tools like MP3 files use this idea to make files smaller. Our ears also respond differently to loud and quiet sounds, which is why things sound louder or softer depending on their volume. This property, called loudness, is used in telephone systems and noise reduction technology.

Limits of perception

The human ear can hear sounds ranging from about 20 to 20,000 Hz, though this range often shrinks with age. Very low frequencies, below what we typically call sound, can sometimes be felt through our sense of touch. Our ears are very sensitive, able to detect tiny changes in sound pressure, from very soft sounds to much louder ones.

People can notice small changes in pitch, especially when two close frequencies create a pulsing effect. Sound loudness is measured on a logarithmic scale, meaning our ears perceive changes differently at various volumes and frequencies. Studies have helped scientists understand how we hear across different pitches and volumes.

Sound localization

Main article: Sound localization

Sound localization is how we figure out where a sound is coming from. Our brain looks at small differences in how loud a sound is, its tone, and when it reaches each ear to determine the sound's position. We can describe this position using three aspects: the side-to-side angle, the up-and-down angle, and how far away the sound is. People, like most animals with four legs, are good at telling where sounds are coming from side to side but not as good up and down because our ears are placed symmetrically. Some owls have ears placed unevenly, which helps them detect sounds from all directions, useful for hunting small animals in the dark.

Masking effects

Main article: Auditory masking

When you try to hear a quiet sound while another louder sound is playing, the quiet sound may become harder to hear. This is called masking. The louder sound that makes it harder to hear the quieter one is called the masker.

Even if the quieter sound is weaker than the louder one, it can still sometimes be heard. Masking can happen when both sounds are played together, like when someone whispers while another person shouts. It can also happen just before or after a loud sound, like a clap, making sounds around it harder to hear. This idea is used in some music file formats to make files smaller.

Missing fundamental

Main article: Missing fundamental

When we hear a series of related tones, such as double, triple, and quadruple the pitch of a certain note, our ears often perceive an additional tone that isn't actually being played. This is called the missing fundamental. It shows how our brain helps us understand sound.

Music

Psychoacoustics studies how we hear and feel music. It helps us understand why certain sounds sound pleasing or calming. Some people use these sounds in music therapy to help others feel better.

Irv Teibel's Environments series LPs from 1969 to 1979 were early examples of sounds made to help improve mood and focus.

Applied psychoacoustics

Psychoacoustics works closely with computer science. Important pioneers like J. C. R. Licklider and Bob Taylor studied psychoacoustics, and companies like BBN Technologies started by focusing on acoustics before developing early networks like the packet-switched network.

Today, psychoacoustics helps create better audio technology. It is used in audio compression formats such as MP3 and Opus, allowing music to be stored in smaller files. It also helps design new audio systems for theaters and homes, and is used in applications like sonification, computer games, drone control, and even image-guided surgery. Musicians use it to enhance sounds, and car makers use it to design engines and doors that sound pleasing.

Perceptual audio coding

See also: Data compression § Perceptual audio coding

Psychoacoustic models help create smaller music files by removing parts of the audio that our ears can't hear well. This means we can make files that are one-tenth to one-twelfth the size of the original, with only a small drop in sound quality. Formats like Dolby Digital, MP3, Opus, Ogg Vorbis, AAC, WMA, MPEG-1 Layer II, and ATRAC use this method.

Our ears have limits to what they can hear, and psychoacoustics studies these limits. This helps audio tools focus on the sounds we notice most and ignore the ones we don't, making files smaller without losing important sound.