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Binaural hearing

2014-11-18 Perceptual effects in binaural hearing

Binaural hearing in humans have evolved through thousands of generations, making it possible to localize sound sources, to estimate distance to the source, to estimate environment geometry, and to enjoy stereophonic music reproduction—to mention a few. Besides, it has a lot of perceptual side effects. By exposing the two ears separately to different combination of artificial sounds, our minds ability to assign direction, broadness and size, etc, to the sounds, can be demonstrated. In these audio examples, headphones should be used.


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Binaural beating

 

1

Sine tone 440Hz, both ears, 6 seconds, soft  start and stop

http://akutek.info/wav/sine440Hz.mp3

2

Sine tone 440Hz at left, 442Hz at right ear

http://akutek.info/wav/sine440L_442R.mp3

2m

Like #2, only mono

http://akutek.info/wav/sine440_442monosum-6dB.mp3

3

Sine tone 440Hz at left, 448Hz at right ear

http://akutek.info/wav/sine440L_448R.mp3

3m

Like #3, only mono

http://akutek.info/wav/sine440_448monosum-6dB.mp3

Comment: #2 and #3 commonly creates the sensation that the sound travels back and forth between left and right, across the head, with cycles equal to the frequency differences, i.e. 2Hz and 8Hz respectively. Sound pressure differences at the two ears apparently add lateral dimension. In their mono-versions, this does not happen. In real life, an effect similar to #2 and #3 could happen if you face a sinusoidal 440Hz source, having a reflecting wall at your right, while the source moves closer to the wall by 1.5m/s and 6m/s respectively. The image source behind the wall would approach your right ear with these velocities, thus creating 442Hz and 448Hz respectively at your right ear, due to the doppler effect. However, since both ears would receive a mix of the two frequencies, the real life effect would be like a mix of #2 and #2m, or a mix of #3 and #3m.

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Gradually increasing ITD (lag in channel R), 440Hz sine wave

 

4

Reference, lag = 0 samples

http://akutek.info/wav/sine440HzR00splag.mp3

5

Lag = 5 samples ITD=0.11ms

http://akutek.info/wav/sine440HzR05splag.mp3

6

Lag = 10 samples ITD=0.23ms

http://akutek.info/wav/sine440HzR10splag.mp3

7

Lag = 20 samples ITD=0.45ms

http://akutek.info/wav/sine440HzR20splag.mp3

8

Lag = 23 samples ITD=0.52ms

http://akutek.info/wav/sine440HzR23splag.mp3

9

Lag = 30 samples ITD=0.68ms

http://akutek.info/wav/sine440HzR30splag.mp3

10

Lag = 40 samples ITD=0.91ms

http://akutek.info/wav/sine440HzR40splag.mp3

11

Lag = 50 samples ITD=1.1ms

http://akutek.info/wav/sine440HzR50splag.mp3

12

Lag = 60 samples ITD=1.4ms

http://akutek.info/wav/sine440HzR60splag.mp3

13

Lag = 70 samples ITD=1.6ms

http://akutek.info/wav/sine440HzR70splag.mp3

14

Lag = 73 samples ITD=1.7ms

http://akutek.info/wav/sine440HzR77splag.mp3

15

Lag = 80 samples ITD=1.8ms

http://akutek.info/wav/sine440HzR80splag.mp3

16

Lag = 90 samples ITD=2.0ms

http://akutek.info/wav/sine440HzR90splag.mp3

17

Lag = 100 samples ITD=2.3ms

http://akutek.info/wav/sine440HzR100splag.mp3

18

Lag = 110 samples ITD=2.5ms

http://akutek.info/wav/sine440HzR110splag.mp3

19

Lag = 120 samples ITD=2.7ms

http://akutek.info/wav/sine440HzR120splag.mp3

20

Lag = 130 samples ITD=2.9ms

http://akutek.info/wav/sine440HzR130splag.mp3

21

Lag = 140 samples ITD=3.2ms

http://akutek.info/wav/sine440HzR140splag.mp3

22

Lag = 150 samples ITD=3.4ms

http://akutek.info/wav/sine440HzR150splag.mp3

 

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Lag and inverted phase

 

23

Sine tone 440Hz, both ears, 6 seconds, soft  start and stop

http://akutek.info/wav/sine440Hz.mp3

24

Like #23, but left channel lagging by half a period (1.14ms or 50 samples)

http://akutek.info/wav/sine440HzLhalflag.mp3

25

Like #23, but right channel lagging by half a period

http://akutek.info/wav/sine440HzRhalflag.mp3

26

Like #23, but right channel inverted (no lag)

http://akutek.info/wav/sine440HzRinverted.mp3

Comment: 24, 25 and 26 may be perceived as ”broader” than 23 and with different loudness than 23. The soft (fade-in) start eliminates the transient que, thus making the half-period lagged examples 24 and 25 and the inverted example 26 hardly distinguishable from one another. Note the brief ”spacious reverb” tails after the ends of 24, 25 and 26.

 

 

 

Looking for listening tests?

http://akutek.info/demo_files/listening_tests.htm

Intimacy in monaural perception:

http://www.akutek.info/demo_files/intimacy_monaural.htm

Proximity in binaural perception:

http://www.akutek.info/demo_files/proximity_perception.htm

Hearing others through the orchestra:

http://akutek.info/demo_files/inter_orchestral_listening.htm

Headphone test 1, sound in Left channel only:    http://akutek.info/wav/sine440HzLeftonly.mp3

Headphone test 2, sound in Right channel only: http://akutek.info/wav/sine440HzRigthonly.mp3

Headphone test 3, sound image should be centered (adjust L-R balance): http://akutek.info/wav/sine440Hz.mp3