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Old 11th Aug 2014, 9:14 pm   #1
John_BS
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Default Non-linearity of the human ear

I was browsing through a couple of old "acoustics" text-books over the weekend, and came upon a description of some experimental work which attempted to quantify the degree to which the ear generates harmonics of pure tones. It struck me as rather elegant, and the method used was as follows:

1. The wanted tone is applied to the human subject at a known sound-power level (raised in stages to eventually generate an audio level v distortion curve).
2. A second pure tone, set to a frequency slightly different to the harmonic to be investigated, is brought up in level until the subject reports a low-frequency beat of maximum amplitude: at this point the second tone is at the same level as the harmonic generated by the ear.
3. The experiment is repeated at several wanted frequencies and for as many harmonics as desired.

The results suggest quite high levels of "distortion", even at modest sound-levels (c. 50dB spl).

A related topic, did you know that hearing loss with age is (on average) quite dramatic: around 30 to 40dB at 4 to 6kHz for 60-year-old men!

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2802451/

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Old 11th Aug 2014, 9:23 pm   #2
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Default Re: Non-linearity of the human ear

When I was about 34, I had a hearing test and the technician/nurse sad I had the hearing of a 60 year old! Apparently this was due to playing in bands with a Marshall plexi in one ear, a loud drum kit in the other.

Oddly, I then went on to become a recording engineer!
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Old 11th Aug 2014, 9:24 pm   #3
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Default Re: Non-linearity of the human ear

Hi Gents, the Mullard book "Transistor Audio & Radio Circuits has an appendix in sound levels, complete with Fletcher Munson curves of the ear's response.

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Old 11th Aug 2014, 9:40 pm   #4
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Default Re: Non-linearity of the human ear

I am one of those of advanced years with hearing loss. The last test I had indicated that my middle frequency hearing was fairly normal but the top response had dropped off considerably, although its still there because I can hear a 10khz tone if its loud enough.

What causes the hearing problem is not being able to hear the sibilance so I miss hear words that start with 'Fs, Ss anf Ts particularly.

I was a TV engineer for 50 years which in the early days was 405 lines, 10.125 kHz and it was deafening to me then, I became so accustomed to it that I could adjust the line hold to frequency then plug the aerial in and the picture would be locked. I could hear if the TV in a house was on outside the front door. I now have tinnitus which sounds like being in a shop full of 405 line TVs - quite nostalgic really.

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Old 11th Aug 2014, 9:49 pm   #5
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Default Re: Non-linearity of the human ear

The way many researchers fall down is that they mechanistically treat the human ear as a simple transducer and don't acknowledge that it's impossible to decouple the ear (or a suitably spatially-installed pair thereof) from its back-end - a rather sophisticated signal-processing unit called The Brain, which overlays a vast slew of adaptive filters on top of the basic physiological ear-response.

Example: many years ago I remember an even-more-ancient operator reliably receiving a morse [CW] signal in the presence of some other nearby and much-stronger signals. Rather than using the 'official' approach of a beat-frequency-oscillator to render the CW signal he wanted as an audible tone he'd turned off the BFO and was essentially using the receiver's background white-noise against which to 'beat' the signal - which appeared as variations in the receiver 'hiss'. His brain did the rest.
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Old 11th Aug 2014, 9:50 pm   #6
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Angry Re: Non-linearity of the human ear

Quote:
Originally Posted by Peter.N. View Post
I am one of those of advanced years with hearing loss.
Ditto here.

Quote:
Originally Posted by Peter.N. View Post
The last test I had indicated that . . . . my top response had dropped off considerably, although it's still there because I can hear a 10kHz tone if it's loud enough.
Lucky you! For anything above 5 kHz, irrespective of its volume, I'm as deaf as a post. Even when I was half the age that I am now, I couldn't hear 10 kHz.

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Old 11th Aug 2014, 10:09 pm   #7
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Default Re: Non-linearity of the human ear

The non-linearity of the human ear has been known for a long time.

Some pipe organs have a 'quint' an added rank of pipes tuned to 1.5 times the frequency of the main rank. These have to be loud ranks because they rely on the ear to mix f and 1.5f to give a beat note at 0.5f. So creating the appearance of sounds a full octave below the main rank.

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Old 11th Aug 2014, 10:23 pm   #8
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Default Re: Non-linearity of the human ear

During my early college years a lecturer did a demonstration of human hearing frequency response. Before testing a number of us student subjects he said that he would be surprised if those of us with the best hearing could hear much above 15 Khz. My friend and I said we could clearly hear line whistle on a 625 set so we expected to do better than that! Both of us managed just under 20 Khz! The lecturer was amazed and actually thought it was some sort of trick, but we repeated the test blindfold and had the same results.
I can still 'just' hear 625 line whistle.
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Old 11th Aug 2014, 10:38 pm   #9
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Default Re: Non-linearity of the human ear

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Originally Posted by Peter.N. View Post
I now have tinnitus which sounds like being in a shop full of 405 line TVs - quite nostalgic really.
I have developed mild tinnitus in the left ear over the last year or so (I'm 59). It's very, very faint, so is only audible in near total silence, such as in bed in the middle of the night. It sounds like a 2kHz sine wave which drops a tone or two intermittently. I suppose I should have a hearing test done, though I'm not conscious of significant hearing loss apart from the usual age related HF loss.
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My friend and I said we could clearly hear line whistle on a 625 set so we expected to do better than that! Both of us managed just under 20 Khz!
Most people in their mid teens can hear up to 20kHz. Those 'mosquito' teenager dispersal devices output a loud tone at about 18kHz which almost nobody over 20 can hear.
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Old 11th Aug 2014, 10:50 pm   #10
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Default Re: Non-linearity of the human ear

I would say most teens can POTENTIALLY hear upto 20 K, it was interesting that non of the others could do better than about 18K. The lecturer, who was about 45, was deaf to anything above 9K, which I though was really bad.
I too have tinnitus, in my right ear, like a hissy whistle at about 3 or 4k. I have a theory that it might be due to years of driving with the rear window partially down in summer.
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Old 12th Aug 2014, 12:11 am   #11
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Default Re: Non-linearity of the human ear

When I was in my mid-50's I picked up a chest infection when I was in hospital for a minor operation and this affected my hearing. What I do well remember is that it upset both the harmonic relationship of sounds, and my sense of sound localisation. Music was so discordant to me that I couldn't enjoy it, and sounds that I knew were from straight ahead, seemed to come from the upper left. I still remember the clashing jangle of discordant sound of the six o'clock news signature tune! Fortunately it only lasted a couple of months.

I remember testing my frequency response using an audio signal generator in the lab when I was in my early 20's, and could then manage up to about 16kHz. I haven't tested it recently, but I can no longer hear the "beep beep" of the electronic alarm of my clock radio in my right ear.
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Old 12th Aug 2014, 12:27 am   #12
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Default Re: Non-linearity of the human ear

When I was very young my parents found out that I had major hearing loss caused by mastoiditis, after operations on both ears my hearing was restored.

As a young man I got into Hi-Fi and I discovered that I could hear frequencies up to 22KHz and spent much effort to find the best configuration for my system.

Now as an old man I find myself with hearing loss again and cannot hear anything above 4-5KHz. I have recently got some of the latest digital hearing aids, but they do not really help as I find they amplify unwanted noises like creaks and cracks when walking across the floor, and do not do anything in a noisy situation except amplify the noise, so that it's like putting ones head in a steel drum.

I feel that my problem is with the actual eardrum, maybe the skin has become hard or maybe it has become soft like an old drum, do not know, but the doctor thinks nerve damage due to my increasing years.

Anyway, I can sympathize with the notion of non linearity of the human ear as in a quiet situation I can still hear somethings quite well.
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Old 12th Aug 2014, 12:47 am   #13
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Default Re: Non-linearity of the human ear

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The lecturer, who was about 45, was deaf to anything above 9K, which I though was really bad.
I can certainly still hear 10kHz, as I use it to align cassette deck heads. The sensitivity may be down though, which I'll only find out about if I have a proper hearing test done.
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Old 12th Aug 2014, 1:04 am   #14
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Default Re: Non-linearity of the human ear

I've recently been prescribed an NHS hearing aid, the fitting of which is quite complex now. A microphone is inserted alongside and gives a real-time graph of your ear's frequency response. The aid is tuned to restore it to normal, just like aligning an IF. I assume the deficiency must therefore be in the eardrum, not the brain.
It will naturally affect some more than others, and at different ages and rates, but I suspect that none of us will escape indefinitely.
In my case, music sounded OK, I had got used to the gradual change and didn't notice it, but it was speech. Everyone mumbled!
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Old 12th Aug 2014, 8:20 am   #15
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Default Re: Non-linearity of the human ear

Most hi-fi amps in the 70s used to have a loudness control. The purpose of this control was to boost the bass and treble frequencies when listening to your system at lower volumes, thus restoring appreciation of those frequencies in the face of our ears 'turning the volume down' on them at lower listening levels. This loudness control was usually fitted as well as normal bass and treble controls. For some strange reason, hi-fi buffs and reviewers thought that these were totally unnecessary, frequently said so, and the control was eventually dropped from amps. My own take on the control would have been to design it with a degree of 'inbuilt intelligence' to operate thus; the control would be set to provide an agreeable amount of low and high frequency boost (if at all) to suit the listener at a certain listening volume. Here's the complicated bit.. any further adjustment of the amp's volume control would automatically change the amount of effect of the loudness control accordingly. ie reduce it's effect at higher volumes and increase it lower volumes, thus, to some extent, matching the non-linearity of our ears.

The fact is our ears are not linear, so the humble loudness control, designed and used properly did have a place in hi-fi amps in my eyes (ears?). The problem with the UK hi-fi market is that fashion and most of the journals embraced the idea that amplification should be 'straight wire' technology. All very well, but this takes no account of our ears, listening preferences and dreadful speaker responses. In short, high quality tone controls - including a well designed and deployed loudness control - have a part to play in a high quality sound system.
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Old 12th Aug 2014, 8:48 am   #16
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Default Re: Non-linearity of the human ear

My preference is to let the ear get on with it and leave the amp flat, after all, thats what happens in the natural world, we hear things according to the ears interpretation.
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Old 12th Aug 2014, 9:08 am   #17
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Default Re: Non-linearity of the human ear

True in the natural world but when you listen at home to a reproduction of the sound you may play it louder or quieter than the 'natural' level and your ears will not hear the 'natural' sound because of the level changes. So I prefer the addition of a loudness control. It should be variable as the input level from a CD player or other item connected to your system may give different signal levels and the effect of the loudness control will vary with the setting of the volume control.
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Old 12th Aug 2014, 9:16 am   #18
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Default Re: Non-linearity of the human ear

Online hearing test:

http://www.noiseaddicts.com/2009/03/...-hearing-test/

I suspect that results may depend, to some extent, on the quality of the playback equipment.

I can hear 14 KHz quite clearly but not 15 K. . . . unless I really crank up the volume and even then I can only just hear it. I also fair well in those perceptive pitch difference tests. Perhaps not bad for someone in their mid 50's. Then again I shunned the Strat and Marshall 4 x 100 W stack for a Lute when I was in my mid '20's.
What a great decision!!
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Old 12th Aug 2014, 9:19 am   #19
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Default Re: Non-linearity of the human ear

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My preference is to let the ear get on with it and leave the amp flat, after all, thats what happens in the natural world, we hear things according to the ears interpretation.
Nowt wrong with helping nature. Listening to music - or speech - can be more enjoyable if you can hear all that's going on. If you leave it to your ailing, non-linear ears, you won't necessarily experience that. I mean, to clarify my position, I'm not looking for an artificially 'boosted', scooped sound with boomy bass and tizzy treble - no way, far from it! - I'm looking for a sound that is balanced, pleasing and 'flat' so that, so to speak, I can hear equal amounts of bass, mids and highs. But we're all different and at the end of the day, our ears are the servants of our brains, and if we - in our brains - have a preference for a listening profile, then that's the way it is, and that's how our brains parse our chosen route to aural pleasure.
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Old 12th Aug 2014, 9:49 am   #20
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Default Re: Non-linearity of the human ear

Re: " My own take on the control would have been to design it with a degree of 'inbuilt intelligence' to operate thus; the control would be set to provide an agreeable amount of low and high frequency boost (if at all) to suit the listener at a certain listening volume. Here's the complicated bit.. any further adjustment of the amp's volume control would automatically change the amount of effect of the loudness control accordingly. ie reduce it's effect at higher volumes and increase it lower volumes, thus, to some extent, matching the non-linearity of our ears."

There was a design which used mechanically centre tapped pots for volume which had the 'Loudness function' attached to them.
This was included in a number of products but unfortunately with the passing of time, I can't remember which ones.

The result was that Loudness compensation was reduced to zero when the Volume pot reached 50 rotation

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