Hypersonic effect
Encyclopedia
The hypersonic effect is a term coined to describe a phenomenon reported in a controversial scientific study by Tsutomu Oohashi
et al., which supports the idea that although humans cannot consciously hear sounds at frequencies above approximately 20 kHz
, the presence or absence of those frequencies has a measurable effect on their psychological reaction. Attempts to independently reproduce these results have so far been unsuccessful.
Numerous other scientific studies have contradicted these results, finding that people who have "good ears" listening to Super Audio CD
s and high resolution DVD-Audio
recordings on high fidelity
systems capable of reproducing sounds up to 30 kHz can't tell the difference between high resolution audio and the normal CD sampling rate of 44.1 kHz.
experiments in which subjects were played music, sometimes containing high-frequency components (HFCs) above 25 kHz and sometimes not. The subjects could not consciously tell the difference, but when played music with the HFCs they showed differences measured in two ways:
It is a common understanding in psychoacoustics
that the ear cannot respond to sounds at such high frequency, so one question that this research raised was: does the hypersonic effect occur via the "ordinary" route of sound travelling through the air passage in the ear
, or in some other way? A peer-reviewed study in 2006 seemed to confirm the second of these options, by testing the different effect of HFCs when presented via loudspeakers or via headphones
- the hypersonic effect did not occur when the HFCs were presented via headphones.
The 2006 study also investigated the comfortable listening level (CLL) of music with and without HFCs, an alternative way of measuring subject response to the sound. The CLL for the music with HFCs was higher than that for the music without HFCs - this provides a quantitative way to demonstrate general listener preference for the music with HFCs.
Researches from NHK
laboratory have attempted carefully but unsuccessfully to reproduce Oohashi's results.
480 man-hours of listening tests conducted at the London AES convention in 1980 by Laurie Finchman of KEF
concluded that subjects could not distinguish a 20 kHz band limited version of a test signal from the original played back on equipment capable of reproducing sound up to 40 kHz.
System non-linearities (present to varying degrees in all audio reproduction electronics, loudspeakers, etc.) are known to produce lower-frequency intermodulation
products when the system is stimulated with high frequency signals. It is suggested that this mechanism could produce signals in the audible range that allow listeners to distinguish the signals. Artifacts like this are a common problem with PC-based hearing self-tests, for instance.
In September 2007, two members of the Boston Audio Society and the Audio Engineering Society
published their study in which about half of the 554 double-blind ABX test
listening trials made by 60 respondents showed the correct identification of high-resolution or CD-standard sampling rate. The results were no better than flipping a coin
.
Tsutomu Oohashi
is a Japanese artist and scientist. He is also known by his pseudonym, .-Early life:Born in Tochigi Prefecture, he attended Tohoku University and graduated from the Faculty of Agriculture...
et al., which supports the idea that although humans cannot consciously hear sounds at frequencies above approximately 20 kHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, the presence or absence of those frequencies has a measurable effect on their psychological reaction. Attempts to independently reproduce these results have so far been unsuccessful.
Numerous other scientific studies have contradicted these results, finding that people who have "good ears" listening to Super Audio CD
Super Audio CD
Super Audio CD is a high-resolution, read-only optical disc for audio storage. Sony and Philips Electronics jointly developed the technology, and publicized it in 1999. It is designated as the Scarlet Book standard. Sony and Philips previously collaborated to define the Compact Disc standard...
s and high resolution DVD-Audio
DVD-Audio
DVD-Audio is a digital format for delivering high-fidelity audio content on a DVD. DVD-Audio is not intended to be a video delivery format and is not the same as video DVDs containing concert films or music videos....
recordings on high fidelity
High fidelity
High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...
systems capable of reproducing sounds up to 30 kHz can't tell the difference between high resolution audio and the normal CD sampling rate of 44.1 kHz.
Favoring evidence
In research published in 2000 in the Journal of Neurophysiology, researchers described double-blindDouble-blind
A blind or blinded experiment is a scientific experiment where some of the people involved are prevented from knowing certain information that might lead to conscious or subconscious bias on their part, invalidating the results....
experiments in which subjects were played music, sometimes containing high-frequency components (HFCs) above 25 kHz and sometimes not. The subjects could not consciously tell the difference, but when played music with the HFCs they showed differences measured in two ways:
- EEG monitoring of their brain activity showed statistically significantStatistical significanceIn statistics, a result is called statistically significant if it is unlikely to have occurred by chance. The phrase test of significance was coined by Ronald Fisher....
enhancement in alpha-wave activity - The subjects preferred the music with the HFCs
It is a common understanding in psychoacoustics
Psychoacoustics
Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound...
that the ear cannot respond to sounds at such high frequency, so one question that this research raised was: does the hypersonic effect occur via the "ordinary" route of sound travelling through the air passage in the ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
, or in some other way? A peer-reviewed study in 2006 seemed to confirm the second of these options, by testing the different effect of HFCs when presented via loudspeakers or via headphones
Headphones
Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...
- the hypersonic effect did not occur when the HFCs were presented via headphones.
The 2006 study also investigated the comfortable listening level (CLL) of music with and without HFCs, an alternative way of measuring subject response to the sound. The CLL for the music with HFCs was higher than that for the music without HFCs - this provides a quantitative way to demonstrate general listener preference for the music with HFCs.
Contrary evidence
There are contradictions in Oohashi's results.- No effect was detected on listeners in the Oohashi study when only the ultrasonic (frequencies higher than 24 kHz) portion of the test material was played for test subjects. The demonstrated effect was only present when comparing full-bandwidth to bandwidth-limited material.
- Bandwidth-limited material was more highly regarded by test subjects when full-bandwidth material was played immediately prior.
Researches from NHK
NHK
NHK is Japan's national public broadcasting organization. NHK, which has always identified itself to its audiences by the English pronunciation of its initials, is a publicly owned corporation funded by viewers' payments of a television license fee....
laboratory have attempted carefully but unsuccessfully to reproduce Oohashi's results.
480 man-hours of listening tests conducted at the London AES convention in 1980 by Laurie Finchman of KEF
KEF
KEF is a British-based loudspeaker manufacturer with international distribution.It was founded in Tovil, Maidstone, Kent in 1961 by electrical engineer Raymond Cooke and named after Kent Engineering & Foundry which previously occupied the site....
concluded that subjects could not distinguish a 20 kHz band limited version of a test signal from the original played back on equipment capable of reproducing sound up to 40 kHz.
System non-linearities (present to varying degrees in all audio reproduction electronics, loudspeakers, etc.) are known to produce lower-frequency intermodulation
Intermodulation
Intermodulation or intermodulation distortion is the amplitude modulation of signals containing two or more different frequencies in a system with nonlinearities...
products when the system is stimulated with high frequency signals. It is suggested that this mechanism could produce signals in the audible range that allow listeners to distinguish the signals. Artifacts like this are a common problem with PC-based hearing self-tests, for instance.
In September 2007, two members of the Boston Audio Society and the Audio Engineering Society
Audio Engineering Society
Established in 1948, the Audio Engineering Society draws its membership from amongst engineers, scientists, other individuals with an interest or involvement in the professional audio industry. The membership largely comprises engineers developing devices or products for audio, and persons working...
published their study in which about half of the 554 double-blind ABX test
ABX test
An ABX test is a method of comparing two kinds of sensory stimuli to identify detectable differences. A subject is presented with two known samples , and one unknown sample X, for three samples total. X is randomly selected from A and B, and the subject identifies X as being either A or B...
listening trials made by 60 respondents showed the correct identification of high-resolution or CD-standard sampling rate. The results were no better than flipping a coin
Coin flipping
Coin flipping or coin tossing or heads or tails is the practice of throwing a coin in the air to choose between two alternatives, sometimes to resolve a dispute between two parties...
.
See also
- Ultrasonic hearingUltrasonic hearingUltrasonic hearing is a recognised auditory effect which allows humans to perceive sounds of a much higher frequency than would ordinarily be audible using the physical inner ear, usually by stimulation of the base of the cochlea through bone conduction...
- Ability to hear ultrasound