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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 .

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

Litterature: Binaural hearing

J Blauert: Spatial Hearing: The Psychophysics of Human Sound Localization

J Blauert (Editor): The Technology of Binaural Listening

J Blauert: Binaural Models and their Technological Application 

Howard and Angus: Acoustics and Psychoacoustics

Fastl and Zwicker: Psychoacoustics. Facts and Models

Floyd Toole: Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms

Gilkey and Anderson: Binaural and Spatial Hearing - in real and virtual environments

M Schröder: Comparative Study of European concert halls: correlation of subjective preference with geometric and acoustic parameters (problems with URL has been reported)

Sue Harding Binaural Processing

Stern, Wang, Brown Binaural Sound Localization

A Oxenham (Lecture) Binaural hearing   

Sound localization (wikipedia)

R.Y Litovsky: Binaural Hearing (external site) 

J Breebaart: Sound Binaural processing model based on contralateral inhibition.I. Model structure

Sound Binaural processing model based on contralateral inhibition.II. Dependence on temporal parameters

Sound Binaural processing model based on contralateral inhibition.III. Dependence on temporal parameters

Misc. Authors: Localization of  sound sources (external site) 

  

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