Psychoacoustics in PA technology
Because PA technology is for people, the interface between technology and perception
You know the specifications of PA amplifiers , the frequency response of speakers and the effects of room modes. But how do you integrate human perception into your technical decisions? The answer lies in psychoacoustics. Psychoacoustics is an important but often underestimated component of many PA applications. It's about understanding how the human brain interprets different noises and sounds and perceives different sound sources. Here are some practical examples of PA technology – as inspiration for future projects.
The perception of sound by the human ear
The ear is a complicated organ consisting of three main parts: the outer ear, the middle ear and the inner ear. Each of these parts has an important function in the perception of sounds. For example, the outer ear helps capture sound waves and direct them to the eardrum, which then passes them on to the middle ear.
The middle ear contains the three smallest bones in the body: the malleus, anvil and stirrup. These bones are very important because they transmit sound waves from the eardrum to the inner ear. This is where the tiny hair cells are found that convert sound into electrical signals, which the brain then processes.
How we perceive sounds also depends on the frequency, amplitude and duration of the sound
- The frequency refers to the number of oscillations per second, measured in Hertz (Hz).
- Amplitude refers to the intensity of a sound measured in decibels (dB).
- Duration refers to the length of a sound, measured in seconds.
An example of how useful psychoacoustics is in PA technology are well-designed conference rooms. A professionally planned conference room should be constructed so that the sound is evenly distributed throughout the room. There should be no point in the room where a participant is disadvantaged by problems with poor perception of the sound. This means that the room must reflect sound in a certain way to achieve the desired sound quality throughout the entire room.
Psychoacoustic basics: FFT, ERB and the critical bandwidth
Fourier transform (FFT)
The fast Fourier transform , usually abbreviated FFT, breaks down an audio signal into its frequency components. The FFT is crucial for analysing masking effects and optimising signal processing. Software tools like MATLAB provide FFT functions to help you with analysis.
Equivalent Rectangular Bandwidth (ERB)
The Equivalent Rectangular Bandwidth indicates how many frequencies the human ear can perceive as "similar". By using ERB in your planning, you can improve sound quality and increase speech intelligibility. Psychoacousticians often use the ERB in spectral analyses to determine the psychoacoustic relevance of frequency bands.
Critical bandwidth
Within the critical bandwidth, people perceive different tones as belonging together. This is crucial when designing PA systems that enable clear voice transmission or music reproduction.
Changi Airport in Singapore uses white noise and natural sounds such as birdsong to create a calming environment that reduces traveller stress.
Binaural technology
Binaural recordings can create a realistic 3D sound experience. By using HRTF (Head-Related Transfer Function), you can control the spatial perception of the sound. This is particularly useful in virtual realities or when designing home cinema systems.
Beamforming
Beamforming is a technology that allows sound to be directed in a specific direction. By using multiple speakers and adjusting the phase and amplitude of the signals they emit, you can create a "beam" of sound oriented in a specific direction.
King's Cross Station in London uses beamforming to direct sound to waiting areas and improve the audibility of announcements.
Examples of application scenarios
Concert hall
In a concert hall, the challenge is to create a balanced sound field for a wide range of frequencies. By applying psychoacoustic principles such as critical bandwidth and ERB, you can optimise the speaker arrangement and the signal processing. This way you can achieve equal sound distribution and minimise phase problems.
Shopping centres and retail stores
In shopping centres and stores, the right PA application is crucial for the customer experience. By applying psychoacoustics, you can design background music so that it is pleasant and does not disrupt conversations. ECMA-418 can serve as a guide for minimising disruptive noise emitted by air conditioning, escalators or other technical installations.
Airports and train stations
In transport hubs such as airports and train stations, clear audibility of announcements is crucial. Psychoacoustic principles can help to improve speech intelligibility by taking into account the acoustic properties of the room and human speech perception.
Hospitals and health facilities
In hospitals, correct application of psychoacoustics can help create a calmer and more comfortable environment for patients. You can achieve this by masking noises such as the beeping of machines or the clattering of dishes.
Sports stadiums
In large sports stadiums, the challenge is to balance both the sound level of the crowd and the clarity of the announcements. By applying psychoacoustics, you can design a system that is optimised for both high and low volume levels – for example from line arrays, which emit sound very precisely.
Museums and exhibitions
In museums, the use of psychoacoustics can help create a more intensive experience. For example, in an art exhibition, a subtle soundscape could complement the presentation of the works without being distracting.
Software tools and measurement methods
Various software tools are available for psychoacoustic analysis, including MATLAB and Audacity. These tools provide A/B testing, loudness scaling, and spectral analysis functions that are essential for measuring psychoacoustic phenomena.
The “ECMA-418” standard
ECMA-418 is a standard of ECMA International, which describes psychoacoustic metrics for ITT (Information Technology and Telecommunications) devices. The second edition was published in December 2022. This standard describes two methods for determining whether noise emissions contain prominent discrete tones:
- the sound-to-noise ratio method
- the prominence ratio method
The psychoacoustic content of ECMA-74 has been moved to ECMA-418 Parts 1 and 2 to separate it from the older regulations on microphone positioning, equipment operation and sound level processing that remain in ECMA-74.
Application examples
Imagine an office where several IT devices such as printers, computers and telephone systems are in operation. By applying ECMA-418 guidelines, you can ensure that these devices are configured to cause minimal acoustic interference. Not only does this improve the work environment, but it can also increase productivity.
Why is ECMA-418 important?
Compliance with ECMA-418 ensures that you apply best practices in psychoacoustics. This is particularly important in environments where sound quality and minimising noise are critical, such as in conference rooms, theatres and other public spaces.
Conclusion: psychoacoustics combines technical know-how with an understanding of human perception
As an installer or expert planner in PA technology, you have the opportunity to use this knowledge to create systems that are not only technically sophisticated but also optimised for the human ear.
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