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Spatial impression and IACC(t)

2016-04-22 Spatial impression from time-varying mix of two pink noise signals: Put on your headphones and make sure that they reproduce stereo correctly (you may want to perform the headphone test 1-3, below). Listen to the 30s audio, which is created quite simply by varying the level balance between a mono signal and a stereo signal.

The stereo signal pair, L and R, are pink noise signals, where L and R are uncorrelated.

The mono signal is the sum signal L+R.

Balance varies contiuously between the extremes at 0s, 5s, 10,s…, 30s, as in the table below.

In the period 20-30s, the signal cross-fades from pure Mono at 20s to pure Stereo at 25s, and finally pure Mono at  30s.

Some listeners may comment that the pure Mono at 0s, 20s and 30s is associoated with a frontal impression, similar to a waterfall at 0 degrees azimuth, heard in anechoic environment, e.g. outdoors.

The equal mix of Mono and Stereo at 5s and 15s would in many listeners produce a wide spatial impression, like a source upfront (at 0 degrees) which is contained in a reverberant room. The stereo component apparently contributes with a perception component often referred to as Envelopment.

At 10s and 25s the binaural signal is pure stereo, and since L and R are uncorrelated, IACC approaches zero. The wide spatial impression is at its extreme. Any impression of a waterfall upfront is vanished, perhaps replaced with two waterfalls, one at the left and one at the right. Do you find this extreme like an enveloping reverberant space or more like two waterfalls in anechoic condition?  

The diagram below  is Inter-Aural Cross-Correlation (IACC) as a function of time, i.e. IACC in 100ms bins. IACC in octaves 125Hz-4kHz are presented as a stacked-area-diagram. Vertical axis is the sum of IACC in all 6 octaves, peaking at the value 6 at 0s, 20s and 30s, where IACC is 1.0 in all 6 octaves.

 

Spatial impression 30s demo, link to MP3 (470kB)

Spatial impression 30s demo, link to WAV  (5MB)

 

 

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

 

Questions? Just ask by mailto:akutek@akutek.info .


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Figure 1 Stacked area .diagram of Inter-Aural Cross-Correlation (IACC) in octaves 125Hz-4kHz as a function of time, i.e. IACC in 100ms bins. Vertical axis is the sum of IACC in all 6 octaves, peaking at the value 6.0 at times 0s, 20s and 30s, where IACC takes the value 1.0 in all 6 octaves simultaneously.

6x1.0 = 6.0

6x0.7 = 4.2

6x0.0 = 0.0

Time

0 s

5s

10s

15s

20s

25s

30s

Mono signal

ON

ON

OFF

ON

ON

OFF

ON

Stereo signal

OFF

ON

ON

ON

OFF

ON

OFF

IACC (each octave)

1.0

0.7

0.0

0.7

1.0

0.0

1.0

Spatial Impression

Frontal

Wide

Extreme Wide

Wide

Frontal

Extreme Wide

Frontal