The loudness war is fought with (and over) compression

Transcription

1 The loudness war is fought with (and over) compression Susan E. Rogers, PhD Berklee College of Music Dept. of Music Production & Engineering 131st AES Convention New York, 2011

2 A summary of the loudness war and its challenges Vickers, E. (Nov. 2010). Journal of the Audio Engineering Society - E-Library. Paper Hypercompression is used to make a signal perceptually louder by concentrating all of the acoustical power in the amplitude range where work is being done. Loudness perception is a summation of acoustical energy over time. Rapidly changing peak energy contributes very little to the overall perceived loudness. Stone, et al. (2009)

3 What is excessive gets excised Listeners frequently judge the louder of two sounds to be better. Music engineers, broadcasters and film sound mixers use compression in part to give the psychological impression that the sound source is powerful and/or nearby. A kind of arms race has ensued among record makers and radio broadcasters to deliver a product that is as loud as the competitor s. Vickers, E. (2010)

4 Distortion is friend and foe Peak clipping causes harmonic distortion. Harmonic distortion can be desired (guitar amps), fondly tolerated (vacuum tube amps), or necessary (timbre perception) but it is implicated in causing listening fatigue. Hypercompressed audio signals are proposed to lead to listening conditions (e.g., longer durations, greater intensity, increased distortion) that risk exposing the listener to damaging effects. Are these assumptions supported? Auditory threshold in 4,400 males, aged years Fleischer, G. (2008)

5 Can hypercompression cause listening fatigue? yes Temporary Level Shift (TLS) Cognitive drain Diminished emotional engagement, lack of interest Hyperactivity of central nervous system

6 Temporary Level Shift (TLS) Epstein, M.J. (2011). Correlates of loudness. In Loudness, Florentine, M., Popper, A.N., and Fay, R.R. (Eds.). Springer:N.Y. Exposure to high-level sounds, particularly for extended periods, causes a reduction in the loudness of sounds (frequency band ~ 4 khz most vulnerable). May result from: reduced neural activity temporary hair cell incapacitation Reduction in the range of db. Asymptotes after 8 hours of exposure. Melnick, W. (1991). Jour Ac Soc Am Recovery by 24 hours.

7 Cognitive drain Stone, M.A. et al (2009). JAES, 57(7/8). Compression can impair sound source perception by linking acoustical energy from separate sources Loss of both temporal and spectral contrasts reduces info available to auditory system Will hypercompression of two simultaneous voice streams increase mental effort? Is co-modulating worse than individually compressed? Greater compression slowed reaction times, esp. for co-modulated signal.

8 Hyperactivity of central nervous system Vickers, 2010 Much anecdotal evidence linking distorted and/or hypercompressed audio to overstimulation of the central nervous system. you end up feeling battered, fatigued by, and disgusted with the music you love... I never heard the word fatigue once when I was cutting vinyl... highly compressed or limited music with no dynamic range is physically difficult to listen to for any period of time... you just stop listening because they fatigue your ear... Increased signal complexity is represented by a corresponding increase in neural activity. But... I am unaware of any studies on this phenomenon... It may be an urban myth.

9 Does hypercompression cause listening fatigue? no Confounded variables and correlations Attention spans and competition for mental resources The auditory system and survival mode

10 The sound source changes, and so does the receiver s behavior, and vice versa Live music unreinforced Recorded music stationary Recorded music portable one room background noise minimal attention maximal at home in car background noise fairly constant attention may be fixed or divided multiple environments background noise changing attention minimal

11 Contrary evidence for widespread hearing loss in noisy environments Fleischer, G. (2008). In Reflections on Sound, Svensson, P. (Ed.). The auditory system can gradually improve in a sonically rich environment where noise is either continual or predictable. 17% of the musicians show auditory damage. 54% of the construction workers show damage.

12 The auditory system and survival mode Fleischer, G. (2008). In Reflections on Sound, Svensson, P. (Ed.). Persons of normal hearing would experience pain at the SPL of the organ tuner. Yet organ tuners have better hearing than other age-matched groups. There is no clear relation between hearing acuity and exposure to long-term continuous noise.

13 The art and skill of compression There remain aesthetic and practical uses for compression. Compression is difficult to reverse engineer. Educating audio engineers to meet this need while preserving fidelity. Educating manufacturers and broadcasters to prevent or reduce distortion by-products. Thank you for listening!