Amplitude panning is a technique in

sound engineering An audio engineer (also known as a sound engineer or recording engineer) helps to produce a recording or a live performance, balancing and adjusting sound sources using equalization, dynamics processing and audio effects, mixing, reproduction, ...

where the same sound signal is applied to a number of

loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or " ...

s in different directions equidistant from the listener. Then, a virtual source appears to a direction that is dependent on

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...

s of the loudspeakers. The direction may not coincide with any physical sound source. Most typically amplitude panning has been used with

stereophonic Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration ...

loudspeaker setup. However, it is increasingly used to position virtual sources to arbitrary loudspeaker setups.

History

First invented by Blumlein in early 1930s, original stereophony was a system that converts the

phase difference In physics and mathematics, the phase of a periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is denoted \phi(t) and expressed in such a scale that it v ...

of the signals recorded by a pair of

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...

s to the amplitude difference of in-phase input signals to two loudspeakers.A. D. Blumlein: Improvements in and relating to sound-transmission, sound-recording and sound-reproducing systems. British Patent No. 34657, 1933.

Operation

Assuming

free field In physics a free field is a field without interactions, which is described by the terms of motion and mass. Description In classical physics, a free field is a field whose equations of motion are given by linear partial differential equati ...

sound propagation In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...

, it has been shown that the

sound field In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...

presented by these two

transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and contr ...

s can deliver an appropriate phase difference between the positions of listener’s ears at low frequencies, where the relation between the position of

phantom image Phantom may refer to: * Spirit (animating force), the vital principle or animating force within all living things ** Ghost, the soul or spirit of a dead person or animal that can appear to the living Aircraft * Boeing Phantom Ray, a stealthy unm ...

and the corresponding

amplitude ratio The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of ampl ...

may be summarized by the so-called ‘ sine law’ (similarly, the tangent law). The system was designed to work approximately below 1 kHz, above which the given phase difference becomes ambiguous, and so does the position of the sound image. However, it was suggested that the localisation at relatively high frequencies may take advantage of the interaural level difference resulting from the head-shadowing effect.F.Rumsey: Spatial audio. Focal Press, London, 2001 For the frontal standard configuration, the relation between the inter-channel level difference and the perceived image position has been investigated in many studies, where the target positions were found to be slightly overestimated in many cases. Similar listening tests were also carried out for some asymmetrical lateral configurations, and the results showed that the amplitude-panning method is not as efficient in presenting images to listener’s side as it is to the front.J. West: Five-channel panning laws: an analytical and experimental comparison. MSc thesis, University of Miami, 1998.

References

{{DEFAULTSORT:Amplitude Panning Stereophonic sound Audio engineering Measurement