I had the pleasure of presenting this paper at the Institute of Acoustics’ conference: Reproduced Sound 2025, Harrogate, UK.
Anyone short on time but interested enough may wish to skip directly to the audio demonstrations. A self-contained HTML file of the presentation is also available, with informative illustrations:
Abstract
Blumlein’s ‘shuffling’ process was designed to correct spatialization anomalies for ‘stereo’ loudspeaker reproduction of baffled, near ear-spaced omnidirectional microphones.
Without shuffling there is a progressive narrowing of the stereo image as frequency decreases.
At low frequencies the elegant sum-and-difference filter network converts arrival-time differences for an oblique source into amplitude differences.
These low-frequency amplitude differences revert to timing differences at the listener; broadband source localization is preserved.
Its lack of widespread use may be attributed to the commonplace consumption of two-channel stereo program using psychoacoustically unequal reproduction formats: a spaced pair of loudspeakers, binaural earphones, and summed-mono devices – a ‘stereo compromise’.
This paper includes a review of Blumlein’s shuffling process and its application to a hybrid near-coincident microphone technique with a central absorbent baffle.In addition, the reciprocal shuffling process is investigated for improved binaural earphone reproduction of program material primarily intended for loudspeakers.
Access to audio demonstrations is provided.
Conclusions
Two-channel near-coincident microphone techniques have the ability to represent excellent and realistic spatialization and balance of acoustic sources and their environment
These features are directly available for binaural earphone reproduction, and readily available for two-channel loudspeaker reproduction via the simplified alt-Blumlein shuffling process —
‘Bass sounds are more correctly aligned in direction with the treble, and the overall result has lower listening fatigue and is generally more natural.’ – Michael Gerzon, 1992 [1,p 22]Blumlein shuffling may be considered an essential tool for near-coincident microphone techniques, offering authentic binaural presentation with a pair of stereo loudspeakers
Blumlein shuffling’s ability to retain cohesive placement of auditory events can be described as improved ‘locatedness’ 1 — spatial distinction and alignment [3,p 4]
Differentiated earphones and loudspeaker versions of ‘stereo’ digital audio formats would allow the audio industries to move beyond the legacy compromise of one version for two non-equal playback conditions.
A listening device could automatically select its appropriate version through the use of metadataInverse alt-Blumlein shuffling may be useful for earphone reproduction of commercially-available two-channel ‘stereo’ program material optimized for loudspeakers; (e.g. a built-in option for personal audio players)
Inverse alt-Blumlein shuffling provides a more natural earphone listening experience for generic amplitude-panned two-channel ‘stereo’ content – in accordance with Duplex theory [4];
(e.g. this simple static function may be inserted on a mix-bus output to in-ear monitors)
Supplementary materials
A complete set of audio examples includes binaural earphone and loudspeaker versions of recordings using a baffled near-coincident microphone technique, and earphone demonstrations of inverse alt-Blumlein shuffling applied to commercially available program material.
Thank you for your interest.
Feedback is encouraged.
Mr Jonathan Digby (Principal investigator)
Researcher
References
