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In the never-ending debate raging in the audiophile community about sound quality and what humans can or cannot hear, it is very very very very incredibly often cited that the upper-limit of the audible range of human hearing is 20 kHz, give or take. Some indicate that this is a conservative estimate, and that the actual upper-limit is actually lower than that (~18 kHz). While others suggest that sounds could be heard or otherwise perceived up to about 25 kHz-30 kHz:

Sampling rates higher than about 50 kHz to 60 kHz cannot supply more usable information for human listeners.

And some others suggest that there is substantial variation between individuals around the upper limit:

The human range is commonly given as 20 to 20,000 Hz, though there is considerable variation between individuals, especially at high frequencies

So is there any biological evidence whatsoever that young, healthy humans can hear or otherwise perceive (or sense) sound waves above 20 kHz? And what would be a conservative estimate of the absolute upper limit of the audible spectrum for humans (i.e. usable sound information for human ears and senses)?

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  • $\begingroup$ Yes. I personally used to top out at 22-23khz. $\endgroup$ – Joshua Jan 22 '15 at 18:45
  • $\begingroup$ @Joshua I'm curious: how was this measured? $\endgroup$ – landroni Jan 22 '15 at 18:51
  • $\begingroup$ Digital frequency generator at constant volume. Kept on increasing frequency until I couldn't hear it. Generator was rated for 32khz. $\endgroup$ – Joshua Jan 22 '15 at 20:37
  • $\begingroup$ The last time I had it working I was about 16. That hardware is broken and the replacement couldn't go high enough to repeat the test. $\endgroup$ – Joshua Jan 22 '15 at 21:40
  • $\begingroup$ @Joshua Interesting. Being 16 at the time (young teenager, NOT an adult) may explain why you were in the whereabouts of 22 kHz. Here's an online High Frequency Range Test (8-22 kHz). $\endgroup$ – landroni Jan 22 '15 at 21:49
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Yes, we can. By means of bone conduction we can hear up to 50 kHz, and values up to 150 kHz have been reported in the young (Pumphrey, 1950). However, it is indeed generally agreed that 20 kHz is the upper acoustical hearing limit through air conduction. The reason for this is debated, but the transfer function of the ossicle chain in the middle ear is a suspected culprit in setting the upper frequency limit to 20 kHz (Hemila et al., 1995).

Hence, using normal speakers or headphones 20 kHz is a very reasonable absolute upper limit. Note that the Nyquist criterium necessitates higher sampling rates (at least 40 kHz), so your statement of using 50k-60k sound cards is correct. If you decide on using bone conduction aids, you might start to think on using higher sampling rates still.

Here is an example of a commercially available bone conduction head set (AfterShockz):

enter image description here

These devices have the potential to increase the upper limit because they bypass the middle ear and hence circumvent the limiting transfer function of the middle ear. They induce vibrations onto the temporal bone, that travel via the bone directly to the inner ear. See the following picture from The High Tech Society:

enter image description here

As a side note: when you grow older the hearing sensitivities at high frequencies are severely reduced, and even the 6 kHz range is severely affected in the elderly (picture from John Perr's website):

HFHL

Disclaimer: I haven't looked into the capabilities in terms of upper frequency limits of bone conduction head sets. I am just talking theoretical limits.

References
- Pumphrey, Nature 1950; 166:571
- Hemila et al., Hear Res 1995; 85:31-44

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  • $\begingroup$ Higher upper limits in the young would make sense to me, as it would explain how very young children (up to 7-8 years) can easily hear and reproduce sounds not present in their native language. About "bone conduction"... Does this also work in cases of listening to audio via headphones, for instance? And would be the approximate mechanism? $\endgroup$ – landroni Jan 21 '15 at 12:39
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    $\begingroup$ I edited the answer - you need bone conduction aids. $\endgroup$ – AliceD Jan 21 '15 at 12:44
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    $\begingroup$ Yeah, I see your point, and that's what I was thinking, too. But that guy seems to be making a serious argument. According to my understanding of his arguments, whether you use 44.1khz or 192khz, the data is always sufficient to perfectly recreate the exact original sinewave (up to the bandwidth limit, here ~22kHz), as per the theory. In each case, there in only one band-limited signal that passes through each sample point, and it is a unique solution (see minutes 5-8 of the video). $\endgroup$ – landroni Jan 21 '15 at 13:05
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    $\begingroup$ Correct. 16 KHz sensitivity for example dwindles in young adults $\endgroup$ – AliceD Jan 21 '15 at 13:41
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    $\begingroup$ Note that the Nyquist sampling limit is the minimum sampling rate necessary to have any hope of reproducing the input signal before the signal becomes unreproducible. At 2*f the reproduced signal is potentially distorted. This works well if you don't care about amplitude distortions but only care about the relative phases of the signal (such as for digital square wave signal) but is very poor at accurately capturing full analog signals. For applications other than audio (such as networking, imaging etc) the rule of thumb is to use 1.5 or 2 times Nyquist frequency. In other words f*3 or f*4. $\endgroup$ – slebetman Jan 22 '15 at 3:46
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If all the processes through which a signal passes are linear, then it makes sense to speak in terms of a maximum useful-content frequency. If a signal passes through non-linear stages, however, it is possible that frequency content which would in and of itself be above the range of hearing, may interact with other frequency content which is also above that range, in such a fashion as produce artifacts which are well within the range of hearing.

A rather annoying example of that may be observed when a GSM cell phone is located near audio equipment. All of the frequency content transmitted by the phone exceeds the upper limit of human hearing by multiple orders of magnitude, and yet the annoying buzz picked up by the audio equipment clearly does not.

What happens is that the frequency content of the cell phone's transmissions contains numerous frequencies which are separated by tens or hundreds of hertz, and many amplifier stages don't completely filter out the radio-frequency content, but are unable to process it without distortion. This distortion causes the amplifier to output sum and difference frequencies, some of which are very much in audible range.

Many kinds of objects and materials will reflect sound waves in a fashion which varies in non-linear fashion with the sounds being reflected. If a diaphragm which had more freedom of movement in one direction than the other were hit with a mixture of 100,000 Hz and 100,100 Hz tones, it would "buzz" at 100 Hz, whereas it would not do so if hit by either tone alone; further, a conventional recording of the combined tones by a high-quality microphone would detect nothing, so playing it back in the presence of the diaphragm would yield no buzz.

It would be rare for aesthetically-pleasing audio content to have frequency content over 20 kHz which contributed materially to its aesthetic aspects. It would certainly be possible, however, to construct frequency content over 20 kHz, however, which could be heard in many common environments, and whose perceived sound would vary in ways that would not be possible using only frequencies below 20 kHz, and would not be implausible that some kinds of musical instruments (e.g. handbells) might produce mixtures of high frequency content which would sound different to different people who found them pleasing, in ways which could not be mimicked using only directly-audible frequencies.

It may be possible for an audio technician working with a functional MRI team to create, for an individual, a sound which was indistinguishable from the original, but for another individual that recreated sound might sound nothing like the original.

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    $\begingroup$ @landroni: I have neither the tools nor expertise to identify the extent to which frequency aliasing caused by intermodulation of ultrasonic-frequency content affects perception in non-contrived cases. I would expect that the eardrum would introduce some distortion because of its asymmetrical loading, and that the details vary between one person and the next, but I don't know the extent of the effect or its variation. I do know that the auditory experience of hearing a handbell concert is different from that of hearing a recording, but I have no idea whether the difference... $\endgroup$ – supercat Jan 21 '15 at 19:26
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    $\begingroup$ ...stems from 20Khz content, 30Khz content, 40Khz content, or something else entirely. A recording at a 44KHz sample rate must not capture anything above 22KHz, though if room acoustics or the microphone caused a combination of higher-frequency sounds to produce a lower-frequency sound, the recording would capture that lower frequency. My main point is that it's entirely plausible that capturing higher frequency content may, in at least some cases, make a recording sound better even if the content itself would not be directly perceptible. $\endgroup$ – supercat Jan 21 '15 at 19:32
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    $\begingroup$ If the listener's ear, when given 60KHz and 55Khz at some amplitude would create a 5KHz signal at a lower amplitude, capturing both frequencies on a 192KHz recording and playing them back would achieve a similar result. Someone with a good computer model of a particular listener's ear might be able to produce a 44.1KHz recording which that person would find indistinguishable from the higher-quality one, but other people might find the two recordings to be different. $\endgroup$ – supercat Jan 21 '15 at 21:32
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    $\begingroup$ @landroni: A C4 handbell sounds a roughly-262Hz fundamental; a C5 is an octave up from that, C6 is two octaves up, etc. Mallmark sells handbells up to C9 (about 8KHz). I can't think of any other instruments other than pipe organs or electronic synthesizers which allow a musician to play notes with a fundamental that high. Since the harmonic richness of a pipe is a function of its height/width ratio and high-pitched pipes are very short, I'm not sure how much predictable ultrasonic harmonic content the highest-pitch pipes have. $\endgroup$ – supercat Jan 22 '15 at 0:15
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    $\begingroup$ I would suggest that, given a 96kHz recording, it should be possible to produce a 44kHz recording aesthetically indistinguishable from the original by applying a tiny amount of distortion or other processing before down-conversion, but the kind of processing required for best results might vary depending upon the nature of the original sound. If an individual would perceive a 96kHz original as aesthetically superior to a "straight" 44kHz conversion, some combination of processing parameters would probably yield a 44kHz file the person would consider to be better yet. $\endgroup$ – supercat Jan 22 '15 at 16:25
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Taken from "24/192 Music Downloads... and why they make no sense":

Sampling rate and the audible spectrum

I'm sure you've heard this many, many times: The human hearing range spans 20Hz to 20kHz. It's important to know how researchers arrive at those specific numbers.

First, we measure the 'absolute threshold of hearing' across the entire audio range for a group of listeners. This gives us a curve representing the very quietest sound the human ear can perceive for any given frequency as measured in ideal circumstances on healthy ears. Anechoic surroundings, precision calibrated playback equipment, and rigorous statistical analysis are the easy part. Ears and auditory concentration both fatigue quickly, so testing must be done when a listener is fresh. That means lots of breaks and pauses. Testing takes anywhere from many hours to many days depending on the methodology.

Then we collect data for the opposite extreme, the 'threshold of pain'. This is the point where the audio amplitude is so high that the ear's physical and neural hardware is not only completely overwhelmed by the input, but experiences physical pain. Collecting this data is trickier. You don't want to permanently damage anyone's hearing in the process.

The upper limit of the human audio range is defined to be where the absolute threshold of hearing curve crosses the threshold of pain. To even faintly perceive the audio at that point (or beyond), it must simultaneously be unbearably loud.

At low frequencies, the cochlea works like a bass reflex cabinet. The helicotrema is an opening at the apex of the basilar membrane that acts as a port tuned to somewhere between 40Hz to 65Hz depending on the individual. Response rolls off steeply below this frequency.

Thus, 20Hz - 20kHz is a generous range. It thoroughly covers the audible spectrum, an assertion backed by nearly a century of experimental data.

enter image description here

Above: Approximate equal loudness curves derived from Fletcher and Munson (1933) plus modern sources for frequencies > 16kHz. The absolute threshold of hearing and threshold of pain curves are marked in red. Subsequent researchers refined these readings, culminating in the Phon scale and the ISO 226 standard equal loudness curves. Modern data indicates that the ear is significantly less sensitive to low frequencies than Fletcher and Munson's results.


This seems to imply that it's highly, highly improbable that anything above 20 kHz could be heard by the human ear, and that in most realistic conditions even that threshold would never be reached. I'm curious if others more knowledgeable can confirm or contradict this...

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protected by AliceD Jan 22 '15 at 11:37

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