The Blumlein Box

Extension

Introduction

The Blumlein Box, AKA BlumBox, is a set of tools for the transformation and analysis of stereo signals. It includes commonly used transforms, such as stereo width and balance, as well as more obscure techniques, like asymmetry and middle panorama. The BlumBox provides an ergonomic stereo workflow for composers and purist recordists alike.

Acknowledgments

Special thanks to Dr. Joseph Anderson, whose paper "Classical Stereo Imaging Transforms--A Review", serves as the basis for this work. The Blumlein Box was developed by Emmett Miller with Dr. Anderson for DXARTS, University of Washington.

For a more detailed tutorial on the BlumBox and illustration of concepts presented in the above paper, see: StereoImagingTransformsIllustrated

Example Workflows

Transforms

The Blumlein Box implements the following 9 stereo transforms:

LR to MS

BlumLRtoMS - Transforms a signal from the LR domain to the MS domain

MS to LR

BlumMStoLR - Transforms a signal from the MS domain to the LR domain

Rotation

BlumRotate - Rotates a stereo signal, preserving relative positions in the stereo field

Width

BlumWidth - Widens or narrows a stereo signal

Balance

BlumBalance - Stereo panning as implemented on most consumer electronics--compresses a stereo signal towards the L or R axis

Middle Panorama

BlumMPan - Rotates the M-axis of a stereo image, leaving the S-axis in place

Asymmetry

BlumAsym - Rotates the S-axis of a stereo image, leaving the M-axis in place

Left Panorama

BlumLPan - Rotates only the L-axis of a stereo image

Right Panorama

BlumRPan - Rotates only the R-axis of a stereo image

Analyses

The Blumlein Box also includes the following 5 stereo imaging analysis functions. Each has the option to return either an instantaneous or time-average value.

Power

BlumFollowPower - Returns the power of a stereo signal

Balance

BlumFollowBalance - Stereo signal balance, i.e. the ratio of the S- to M-axis

Correlation

BlumFollowCorrelation - Degree of similarity between left and right channels, i.e. the distribution of energy along the M-S axis.

Angle

BlumFollowAngle - Apparent source direction of a stereo image in radians

Radius

BlumFollowRadius - Encoding radius of a stereo image

Further Reading

1. Anderson, J. L., "Classic Stereo Imaging Transforms: A Review", published in Spanish in Basso, G., Di Liscia, O. P. & Pampin, J. (editors)(2009). "Música y espacio: ciencia, tecnología y estética". Buenos Aires, Universidad Nacional de Quilmes.
2. Streicher, Ron., and F. Alton Everest. The New Stereo Soundbook. Audio Engineering Associates, 2006.
3. American reprint: Blumlein, A. D. (1958). "British Patent Specification 394,325 'Improvements in and relating to Sound-transmission, Sound-recording and Sound-reproducing Systems'" http://decoy.iki.fi/dsound/ambisonic/motherlode/source/British%20patent%20specification%20394325%20Blumlein%201933.pdf (PDF). Journal of the Audio Engineering Society. 6 (2): 32–40.