“Improved Localization for Binaural Recordings and Stereo Program Material Using Blumlein Shuffling” by Jonathan Digby, Adam Hill and Bruce Wiggins examines how a somewhat forgotten stereo processing technique can significantly enhance spatial localisation when binaural and near-coincident recordings are played back over earphones or loudspeakers. The paper offers practical insight into correcting image narrowing, with clear relevance for recording engineers, researchers and anyone working with stereo or binaural audio reproduction.
What is the title of the paper?
Improved Localization for Binaural Recordings and Stereo Program Material Using ’Blumlein shuffling’
What is the paper about?
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.
Why should people be interested in this work?
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. Shuffling may be considered an essential tool for near-coincident microphone techniques, offering authentic binaural presentation with a pair of stereo loudspeakers.
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 metadata.
Inverse 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 (e.g. this simple static function may be inserted on a mix-bus output to in-ear monitors).
SUPPLEMENTARY MATERIAL
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.
https://digbyphonic.com/research/rs2025/RS2025supplements.html
What’s the full citation for the paper?
J. J. Digby, A. J. Hill, and B. J. Wiggins, ‘Improved Localization for Binaural Recordings and Stereo Program Material Using ’Blumlein shuffling’’, in Reproduced Sound 2025, Harrogate, UK: Institute of Acoustics, 2025.
Where can the paper be accessed online?
https://digbyphonic.com/posts/20251203_IoA_paper2/ImprovedLocalizationCounter.php