Sensitivity of human hearing

[retroman]

Hi all,

I'm not an expert at reading SPL/frequency/impedance charts but am curious... Does anyone happen to know when we humans can begin to hear a change in the amount of decibels? Can we hear a difference say between 1 and 2 decibels? Or does it take more than that to tell?

Your advice and opinions are appreciated.


Thanks,
Retroman

[mwmkravchenko]

What!

I couldn't resist.

The answer to your question is a bit mixed. A change in Sound Pressure Level of 1 decibel is the threshold of most people to distinguish a difference in sound level in a very quiet environment. Be louder or softer. What most people consider twice as loud is 10 decibels. Or 1 Bell.

When real life catches up to us in normal environments that are busy and noisy a difference in about 3 db is what most people detect as a change up or down.

People with acute hearing can hear even less than a decibel. For instance people who play a musical instrument tune to 10ths of 1 hz and listen intently to small and subtle changes in loudness. Most people when trained can do this as long as they don't have any significant hearing loss. It's a bit of being aware of what goes on and you start to pay attention to it more.

Hope this helps a bit.

Mark

[jcx]

http://www.provide.net/~djcarlst/abx_crit.htm

[CLS]

Playing with EQ and RTA simultaneously (like sound card or something like DEQ2496), you may judge for yourself. 'Practicing' with them make 'better' sensitivity to an extent.

In the mid-high frequency range, narrow band difference of 1db within pink noise is audible (to me). Not significant though. As Mark stated above, you have to concentrate to distinguish the difference. If the loudness difference is applied to a wider range, say 1-2 octaves or larger, than it'll be easier to detect.

[Pano]

That's an interesting way to do it - with pink noise bands. Thanks for that.

[bear]

This is a question that is often misunderstood because of the textbook definitions.

A difference of 1.5dB SPL is called a "JND" or Just Noticeable Difference". This is for single tone discriminations.

If you use "pink noise" you can hear far lower level differences in levels, especially when you shift a wide bandwidth within a larger bandwidth (like a small xover tweak).

You are unlikely to be able to discriminate very fine differences using normal program sources like voice or music. In fact you will be hard pressed to even hear a JND with normal program sources.

That does not mean that the overall presentation of the soundfield is unaffected by minor (less than JND) tweaks of levels (EQ, xovers, shelving, etc...) in a speaker.

_-_-bear

[Gabdx1]

At 1khz you can roughtly discern 325 degres of intensity from 10db - 130 db, 0 db = can't hear anything.

The answer is somewhere around 1/3 db and is 'ear' dependant and frequency dependant.

The audition spectrum spread somewhere between 16-20khz.

Musicality starts around 35hz and ends at 15khz.

To be able to hear under 35 hz or over 15khz the sound pressure needs to be painful. To hear 20khz = 100db, to hear 20hz = 85db.

[CLS]

Originally posted by bear
...

You are unlikely to be able to discriminate very fine differences using normal program sources like voice or music.

....

Indeed.

So, in reverse, if you 'fine tune' the system under pink noise, which is easier to judge the tonal balance and measure, and then play the music. It'd be smoother. It's like an exam which can pin point the 'problem'.

[Thunau]

I always found this bit of information striking:

http://hyperphysics.phy-astr.gsu.edu...arsens.html#c1

"The human ear can respond to minute pressure variations in the air if they are in the audible frequency range, roughly 20 Hz - 20 kHz.
It is capable of detecting pressure variations of less than one billionth of atmospheric pressure. The threshold of hearing corresponds to air vibrations on the order of a tenth of an atomic diameter. This incredible sensitivity is enhanced by an effective amplification of the sound signal by the outer and middle ear structures. Contributing to the wide dynamic range of human hearing are protective mechanisms that reduce the ear's response to very loud sounds.

[Gabdx1]

Yes, that is copied from my book ! this 1/10 diameter is at 3000hz only. Don't forget this is the AMPLITUDE, still a very soft vibration at other levels of frequency less than 2khz and more than 3khz there is 10db loss of sensitivity and climbing.