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  • Rory Conder

Psychoacoustics in Surround Sound Theory

Psychoacoustics:


localisation of a sound source depends on 3 factors:

  1. The level difference between the ears from the sound source

  2. The time difference between the ears from the sound source

  3. Complex frequency changes due to Human Related Transfer Functions (HRTF) e.g. the head moving etc.

Static and Dynamic


HRTF's affect frequency so EQ must be used differently for surround speaker sources in order to maintain the timbre of the original source.


The minimum audible angle varies around a sphere encompassing our heads and is best front/horizontal, gradually getting worse towards the sides, rear, above and below.



Low frequency enhancement (0.1 channel) is psychoacoustically based giving greater headroom to the other channels. Localisation of low frequencies is poor so subwoofers are needed.


Effects such as timbre changes, localisation, (panning), and stereo width (potentially with reverb, Hass effect digital time delay), can affect localisation of the sound source.


Instruments panned between front & surround channels are subject to image instability and sounding "split-in-two". This means it is better to position primary sources within the front L,C,R speakers.


Phantom image stereo is fragile with listening positions and has frequency response anomalies.


In a multichannel audio playback system a phantom image can sometimes be created between any two (or more) of the loudspeakers, creating the illusion of an additional speaker or (more importantly) adding to the overall realism of the soundstage. For example, in a simple left/right speaker setup it is possible to create a convincing phantom center image if the system is well designed and the audio produced well.






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