סימוכין, לבקשת עופר.
הראשון הוא מחקר מדעי המראה שהמוח מושפע מרכיבים הרמוניים מעל 20 קה"ץ:
http://jn.physiology.org/cgi/content/full/83/6/3548
כאן מעניין הקטע הבא:
[left]
Although it is generally accepted that humans cannot perceive sounds in the frequency range above 20 kHz, the question of whether the existence of such "inaudible" high-frequency components may affect the acoustic perception of audible sounds remains unanswered. In this study, we used noninvasive physiological measurements of brain responses to provide evidence that sounds containing high-frequency components (HFCs) above the audible range significantly affect the brain activity of listeners. We used the gamelan music of Bali, which is extremely rich in HFCs with a nonstationary structure, as a natural sound source, dividing it into two components: an audible low-frequency component (LFC) below 22 kHz and an HFC above 22 kHz. Brain electrical activity and regional cerebral blood flow (rCBF) were measured as markers of neuronal activity while subjects were exposed to sounds with various combinations of LFCs and HFCs. None of the subjects recognized the HFC as sound when it was presented alone. Nevertheless, the power spectra of the alpha frequency range of the spontaneous electroencephalogram (alpha-EEG) recorded from the occipital region increased with statistical significance when the subjects were exposed to sound containing both an HFC and an LFC, compared with an otherwise identical sound from which the HFC was removed (i.e., LFC alone). In contrast, compared with the baseline, no enhancement of alpha-EEG was evident when either an HFC or an LFC was presented separately. Positron emission tomography measurements revealed that, when an HFC and an LFC were presented together, the rCBF in the brain stem and the left thalamus increased significantly compared with a sound lacking the HFC above 22 kHz but that was otherwise identical. Simultaneous EEG measurements showed that the power of occipital alpha-EEGs correlated significantly with the rCBF in the left thalamus. Psychological evaluation indicated that the subjects felt the sound containing an HFC to be more pleasant than the same sound lacking an HFC. These results suggest the existence of a previously unrecognized response to complex sound containing particular types of high frequencies above the audible range. We term this phenomenon the "hypersonic effect."
[/left]
אגב, זה שולל את ההשערה של DigiSUN שמדובר באפנון-הדדי היוצר רכיבים מתחת ל- 20 קה"ץ.
קטעים נוספים שאינם מחקר מדעי:
http://www.d-r.nl/dnrsite/service/faq/A ... gital.html
כאן מעניין הקטע הבא:
[left]
If we all agree on this, it means that we can hear or at least notice signals beyond 20kHz.
Remember the first harmonic content above 12kHz is 24kHz , and then 36kHz and so on.
These generated frequencies above 20kHz (even in small amounts) prove that it is important to have an audio system that has a bandwidth well over 20kHz.
If you repeat this test for a fundamental of let’s say 16kHz, the first order harmonic is around 32khz and higher. Even on this frequency most of the experienced professional listeners could easily determine when they were listening to a sine wave or a square wave!
Amazingly is not it? At least I was amazed and immediately knew why we should continue making our console having a bandwidth of 100kHz and higher.
We trim our op-amps on the board for as long as I can remember to be stable at 40kHz square waves without overshoots and frequency roll off. We are convinced that if we tune our op-amps this way they are capable of amplifying any sum or difference of the fundamental frequency within the audio band without any coloration. Our reputation for perfect sounding consoles proved we were right.
The simple test described above proves that we are capable of perceiving sound information well above 20kHz and that this information absolutely leads to a warmer and richer sound . How we humans are doing this is still a miracle to me and many others I heard.
It is absolutely a fact that a small lift in frequency response of audio equipment well above 20kHz could easily give you the impression of giving you more air or transparency. Based on this principle we have designed our equalizers in a way that the upper band is lifting the fundamental frequency well above 20kHz if needed., resulting in a smooth breeze of air in your control room sound wise.
[/left]
http://www.dspguide.com/ch22/2.htm
כאן מעניין הקטע הבא:
[left]
It is often said that timbre is determined by the shape of the waveform. This is true, but slightly misleading. The perception of timbre results from the ear detecting harmonics. While harmonic content is determined by the shape of the waveform, the insensitivity of the ear to phase makes the relationship very one-sided. That is, a particular waveform will have only one timbre, while a particular timbre has an infinite number of possible waveforms.
The ear is very accustomed to hearing a fundamental plus harmonics. If a listener is presented with the combination of a 1 kHz and 3 kHz sine wave, they will report that it sounds natural and pleasant. If sine waves of 1 kHz and 3.1 kHz are used, it will sound objectionable.
[/left]
http://www.audioholics.com/education/au ... ity-part-1
כאן מעניין הקטע הבא:
[left]
Many people have commented that CDs do not seem to reproduce high frequencies as well as analog sources such as vinyl and magnetic tape. Perhaps the above could at least partially explain the subjective impressions? This would also suggest one benefit of sampling at higher rates such as 96kHz or 192kHz even though our ears cannot hear past 20kHz. A higher sampling rate can help preserve amplitude and harmonic accuracy for non-sine waves at high frequencies.
[/left]
http://digitalcontentproducer.com/mag/a ... eyond_khz/
כאן מעניין הקטע הבא:
[left]
The human hearing system uses waveform and frequency to analyze signals. It is important to maintain accurate waveform up to the highest frequency region with accurate reproduction of details down to 5 ms to 10 ms. The accuracy of low-frequency details is equally important. We find many low-frequency sounds, such as drums, take on a remarkable strength and emotional impact when waveform is exactly reproduced. Please notice the exceptional drum sounds on The Dead Can Dance album Into the Labyrinth. The drum sound seems to have a very low fundamental, maybe about 20 Hz. We sampled the bitstream from this sound and found that the first positive waveform had twice the period of the subsequent 40 Hz waveform. Apparently, one half cycle of 20 Hz was enough to cause the entire sound to seem to have a 20 Hz fundamental.
The human auditory system, both inner and outer hair cells, can analyze hundreds of nearly simultaneous sound components, identifying the source location, frequency, time, intensity and transient events in each of these sounds simultaneously, and it can spatially map these sounds with awareness of each sound source, its position, character, timbre, loudness and all other identification labels that we can attach to sonic sources and events. I believe that this sound quality information includes waveform, embedded transient identification and high-frequency component identification to at least 40 kHz (even if you cannot hear these frequencies in isolated form). To meet the requirements of human auditory perception, a sound system must cover the frequency range of about 15 Hz to at least 40 kHz (some say 80 kHz or more) with more than 120 dB dynamic range to handle transient peaks properly and with a transient time accuracy of a few microseconds at high frequencies and 1 degrees or 2 degrees phase accuracy down to 30 Hz. This standard is beyond the capabilities of modern systems, but it is important that we understand the degradation of perceived sound quality resulting from compromises made in today's sound-delivery systems. The transducers are the most obvious problem areas, but the storage systems and all the electronics and interconnections are important, too.
[/left]
