Glossary

11.2 Loudness perception and equal-loudness contours

3 min read•july 24, 2024

perception is a complex interplay between physics and psychology. It's not just about how loud a sound is, but how our brains interpret it. This topic explores the relationship between objective sound measurements and our subjective experience of volume.

Understanding loudness perception is crucial for everything from designing headphones to creating effective noise regulations. We'll dive into how our ears respond differently to various frequencies and intensities, and how scientists quantify these subjective experiences.

Loudness Perception Fundamentals

Loudness and sound pressure level

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  • Loudness
    • Subjective perception of sound intensity reflects how humans experience volume
    • Psychological correlate of sound's physical amplitude varies between individuals
  • Relationship to (SPL)
    • Measured in decibels (dB) quantifies sound pressure objectively
    • Logarithmic scale compresses wide range of pressures into manageable numbers
    • Doubling of perceived loudness ≈ 10 dB increase in SPL demonstrates non-linear relationship
  • Frequency dependence
    • Human ear sensitivity varies with frequency affecting perceived loudness
    • Most sensitive range: 2-5 kHz aligns with speech frequencies
    • Less sensitive at low and high frequencies requires higher SPL for equal loudness perception

Equal-loudness contours and hearing

    • Curves representing combinations of frequency and SPL perceived as equally loud illustrate hearing sensitivity
    • Measured in phons standardizes loudness across frequencies
    • Original equal-loudness contours (1933) pioneered psychoacoustic research
    • Revised by Robinson-Dadson (1956) and :2003 improved accuracy
  • Implications for hearing sensitivity
    • Non-linear of human ear affects sound perception
    • Increased sensitivity in 2-5 kHz range enhances speech recognition
    • Reduced sensitivity at low and high frequencies impacts music and environmental sound perception
  • Applications
    • Audio equipment design optimizes sound reproduction for human hearing
    • Noise control and assessment considers frequency-dependent loudness perception
    • Hearing protection standards account for equal-loudness contours

Loudness scaling in psychoacoustics

    • Methods to quantify subjective loudness perception enable objective measurements
    • Relates physical sound parameters to perceived loudness bridges physics and psychology
    • Unit of perceived loudness provides linear scale for subjective experience
    • 1 sone = loudness of 40 dB SPL at 1 kHz establishes reference point
    • Doubling of sones = doubling of perceived loudness simplifies loudness comparisons
    • L=k∗InL = k * I^n models relationship between physical intensity and perceived loudness
    • L: perceived loudness, I: sound intensity, k: constant, n: power exponent (typically 0.3 for loudness)
  • Applications in
    • Hearing aid design and fitting improves user experience
    • Sound quality assessment enhances product development (cars, appliances)
    • Audio compression algorithms optimize data reduction while preserving perceived quality

Loudness vs sound intensity

  • Sound intensity
    • Objective measure of sound energy quantifies physical properties
    • Measured in watts per square meter (W/m²) indicates energy flow
    • Proportional to the square of sound pressure relates to measurable acoustic parameters
  • Loudness vs. sound intensity
    • Loudness: subjective perception varies between individuals and contexts
    • Intensity: physical property remains constant regardless of listener
  • Relationship to human perception
      • Perceived sensation is proportional to the logarithm of the stimulus intensity explains non-linear loudness perception
    • (JND)
      • Smallest detectable change in stimulus intensity varies with sound level
      • Varies with frequency and overall sound level affects perceptual resolution
  • Factors affecting loudness perception
    • Duration of sound influences perceived loudness (temporal integration)
    • Spectral content affects perceived loudness (frequency components)
    • Temporal patterns impact loudness perception (amplitude modulation)
    • Spatial distribution of sound sources influences perceived loudness (localization cues)

Key Terms to Review (23)

A-weighting: A-weighting is a frequency weighting used in sound measurement that emphasizes the frequencies most relevant to human hearing, particularly in the mid-frequency range. This method modifies the sound level measurements to reflect the perceived loudness of different frequencies, making it essential for assessing environmental noise and understanding how people perceive loudness across various contexts.
Audio Mixing: Audio mixing is the process of combining multiple audio tracks into a single output, adjusting levels, panning, and applying effects to create a balanced and cohesive sound. This process is essential in music production, film scoring, and live sound reinforcement, where the final mix must accurately reflect the intended artistic vision. Understanding how different frequencies interact and how loudness perception influences mixing choices is crucial for achieving a polished result.
Auditory sensitivity: Auditory sensitivity refers to the ability of the auditory system to detect and perceive sounds at various frequencies and intensities. This concept is crucial in understanding how humans perceive loudness, as our sensitivity varies across different frequencies, which influences how we experience sound intensity in everyday life. Factors like age, hearing loss, and environmental conditions can impact this sensitivity, making it a vital aspect of sound perception.
C-weighting: C-weighting is a frequency weighting used in sound level meters to measure noise levels with an emphasis on the mid to high frequencies, particularly around 1000 Hz to 6000 Hz. This method reflects how the human ear perceives loudness at higher sound levels, making it particularly useful for assessing loud environments and evaluating sound exposure in terms of potential hearing damage or discomfort.
Critical Band: The critical band refers to a specific range of frequencies around a given tone within which other nearby sounds can interfere with the perception of that tone. This concept is essential in understanding how humans perceive loudness and how sounds blend or mask each other in complex auditory environments. The critical band plays a significant role in the shape of equal-loudness contours, as it influences how different frequencies contribute to the overall loudness that we perceive.
Decibel: A decibel is a logarithmic unit used to measure the intensity of sound, specifically in relation to a reference level. It provides a way to quantify sound levels, making it easier to understand the differences in loudness and intensity. By using this scale, we can compare sounds of different amplitudes, determine sound pressure levels, and understand how sound behaves in various environments.
Equal-loudness contours: Equal-loudness contours are graphical representations that illustrate how the perceived loudness of sounds varies with frequency at a constant sound pressure level. These curves show that the human ear's sensitivity to different frequencies is not uniform, meaning certain frequencies need to be louder than others to be perceived as equally loud. This concept is crucial in understanding loudness perception and how it relates to sound quality and audio engineering.
Fletcher-Munson Curves: Fletcher-Munson curves, also known as equal-loudness contours, represent how the human ear perceives loudness at different frequencies. These curves illustrate that our sensitivity to sound varies with frequency, meaning sounds of the same intensity can be perceived as differently loud depending on their pitch. The curves help to understand loudness perception and provide a basis for designing audio equipment and sound environments that cater to human hearing.
Frequency Response: Frequency response refers to the measure of an audio system's output spectrum in response to a range of input frequencies. It provides insights into how well a system can reproduce different frequencies, indicating the strengths and weaknesses in sound reproduction. This characteristic is crucial for understanding concepts like acoustic impedance, loudness perception, filtering, sound reinforcement, and modeling in acoustics.
ISO 226: ISO 226 is an international standard that defines the equal-loudness contours of human hearing, which represent how loud different frequencies sound to the average human ear at various sound pressure levels. This standard provides a framework for understanding loudness perception, helping to illustrate that the human ear does not perceive all frequencies equally at a given volume. The equal-loudness contours depicted in ISO 226 are crucial for audio engineering and sound design as they inform how sounds should be mixed and reproduced to match human auditory perception.
Just Noticeable Difference: Just noticeable difference (JND) refers to the smallest change in a stimulus that can be detected by an observer. In the realm of sound, it highlights the thresholds at which a listener can perceive differences in sound levels or pitches. This concept is crucial for understanding how sound intensity is measured on the decibel scale and how loudness is perceived across different frequencies through equal-loudness contours.
Loudness: Loudness is the subjective perception of sound intensity, which relates to how we experience sound rather than its physical measurement. It varies based on sound wave characteristics, including amplitude and frequency, and plays a critical role in applications across different fields such as acoustics. Understanding loudness helps in designing spaces like concert halls, where the experience of sound is influenced by factors such as reverberation time and the equal-loudness contours that describe how humans perceive different frequencies at varying loudness levels.
Loudness scaling: Loudness scaling is a method used to quantify the perception of loudness in relation to sound intensity levels. This concept connects how humans perceive different sound levels with a focus on the way loudness can change based on frequency and sound pressure levels. It emphasizes the subjective experience of loudness and helps create equal-loudness contours, which illustrate how the human ear responds to various frequencies at equal perceived loudness.
Masking: Masking refers to the phenomenon where the perception of one sound is affected by the presence of another sound, making it harder to hear the first sound. This effect can significantly alter how we perceive sounds in various contexts, including music and speech, by affecting the clarity and loudness of the target sound in the presence of competing noises.
Perceptual evaluation: Perceptual evaluation refers to the subjective assessment of auditory stimuli based on human perception, particularly focusing on qualities like loudness and timbre. It plays a critical role in understanding how individuals experience sound in relation to equal-loudness contours, which represent how the perceived loudness of sounds varies with frequency. This evaluation helps us understand the relationship between physical sound properties and human auditory experience.
Phon: A phon is a unit of measurement used to quantify perceived loudness in human hearing, based on the equal-loudness contours of sounds. It helps represent how loud a sound is perceived at different frequencies, allowing for a more accurate understanding of how humans experience loudness compared to sound intensity alone. This measurement is crucial for understanding the relationship between sound pressure level and the human auditory system.
Psychoacoustics: Psychoacoustics is the study of how humans perceive sound, encompassing the psychological and physiological responses to auditory stimuli. It connects sound properties, such as frequency and intensity, with how we interpret them in terms of loudness, pitch, and timbre. This area of study has evolved through historical advancements in acoustics and is crucial for understanding loudness perception and the construction of equal-loudness contours.
Sone Scale: The sone scale is a unit of measurement for loudness perception that quantifies how loud a sound is perceived to be by the human ear. It is based on a logarithmic scale where a sound that is 10 sones is perceived to be twice as loud as a sound that is 1 sone. This scale connects deeply to how we perceive loudness and is crucial for understanding equal-loudness contours, which illustrate how the human ear's sensitivity to sound varies across different frequencies and sound pressure levels.
Sound engineering: Sound engineering is the technical discipline of manipulating audio elements to achieve desired sound quality and effects in various applications like music production, film, and live performances. It encompasses recording, mixing, and mastering audio while understanding the principles of acoustics and sound perception. This field also heavily involves the use of equipment such as microphones, mixers, and software to create the best auditory experience for listeners.
Sound Pressure Level: Sound Pressure Level (SPL) is a measure of the pressure variation from a reference level, typically 20 µPa in air, and is expressed in decibels (dB). This measurement quantifies the intensity of sound as perceived by the human ear and is essential for understanding how sound behaves in different environments, impacting areas such as sound reinforcement, environmental noise management, and loudness perception.
Stevens' Power Law: Stevens' Power Law describes the relationship between the magnitude of a stimulus and the perceived intensity or loudness of that stimulus, stating that perceived intensity is proportional to the stimulus raised to a power. This principle helps to explain how our perception of loudness varies with changes in sound intensity, revealing non-linear characteristics that differ across various types of sensory experiences.
Subjective testing: Subjective testing refers to methods of evaluation based on personal opinions, interpretations, feelings, or experiences, rather than objective measurements or criteria. In the context of loudness perception, subjective testing is crucial as it captures individual responses to sound stimuli, revealing how different frequencies and sound levels are perceived by listeners. This approach often involves listener panels or surveys to gather data on perceived loudness across varying sound conditions.
Weber-Fechner Law: The Weber-Fechner Law is a principle in psychophysics that describes the relationship between the magnitude of a stimulus and the corresponding sensation it produces. This law states that the perceived change in a stimulus is proportional to the original stimulus's intensity, emphasizing how our perception of loudness is not a linear relationship but rather follows a logarithmic scale. This principle helps explain how we perceive differences in sound intensity and forms the basis for equal-loudness contours, which illustrate how different frequencies are perceived at varying loudness levels.
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