On the Audibility of Phase

Just found this compilation of references to the advantages of linear phase speakers (from various authors), on the Linkwitz Labs web site:

http://www.linkwitzlab.com/Attributes_Of_Linear_Phase_Loudspeakers.pdf

If you read it, you too might just be a little bit curious about how this stuff sounds..? What it is saying is that a conventional speaker no matter how high end, cannot rival a full-fat DSP-based speaker in terms of the ear’s two stage process of responding first to transients, and only then to the spectral information.

…there is a volume of research results that clearly indicates, that rather than asking “is phase distortion audible?” we should now be asking question “how does the phase distortion manifest itself?”….

“…..Another area in which loudspeakers are disreputable is in the neglect of the time domain. The traditional view is that all that matters is to be able to reproduce continuous sine waves over the range of human hearing.

A very small amount of research and thought will reveal that this is a misguided view. Frequency response is important, but not so important that the attainment of an ideal response should be to the detriment of realism. One tires of hearing that “phase doesn’t matter” in audio or “the ear is phase deaf”. These are outmoded views which were reached long ago in flawed experiments and which are at variance with the results of recent psychoacoustic research….

…Linear-phase loudspeakers offer everything that minimum-phase loudspeakers can offer, and then reward you with often vastly superior performance in time domain, as explained in the pages above.

It appears, that my poor and outdated listening/evaluating habits, coupled with lack of standard listening methodology for time/space-domain assessment of loudspeakers conspired to cloud my ability to really critically listen to the full set of my loudspeakers during some of my evaluation tests. …

…I pointed out earlier the effect of feeling closer to the orchestra, as if I could better discriminate their sitting arrangement. Both of these effects have really nothing to do with frequency domain – they are both more of the time/space domain phenomena.

…At the time of this writing, linear-phase loudspeakers are still a new “kid on the block”. Past attempts in creating them resulted in offerings that were simply too expensive for wide-spread use. The most accurate implementation of linear-phase loudspeaker requires a full set of individual driver measurements, coupled with a DSP approach, in addition to an active amplification system. This really makes the linear-phase system highly customized device – a world of difference in comparison to the current approach of loudspeaker industry….

It is clear, that designing loudspeakers using frequency-domain characteristics as the main (or only) criteria leads to stagnated, oversimplified, and ultimately inaccurate system. If I continued to design loudspeakers that never reveal time-domain or spatial-domain subtleties, I would never even know of the existence of such subtleties, therefore, I would never be motivated to change – thus allowing the vicious cycle to continue. It is evident, that the ear examines the incoming audio stimulus in two-stage process: (1) location – here the transient of the stimulus is examined, and (2) signal – here the spectral properties of the stimulus are examined. The two processes always work in-tandem. It is therefore essential, that the loudspeaker provides undistorted waveforms to the auditory system to enable correct processing of both stages.

So, here I am. Struggling to come out of the “frequency-domain box” and into the new world of time/frequency/space-domain characteristics of contemporary loudspeakers. But even at these early stages of adopting a new technology, I find it already very rewarding. This is because it’s evident that a new, accurate and realistic acoustic transduction technology is being achieved in much more accessible commercial way.

There’s lots more interesting stuff in the paper.

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2 thoughts on “On the Audibility of Phase

  1. Thank you for posting such a thought provoking and fascinating article.

    Up until today I had believed the prevailing orthodoxy about phase effects being essentially inaudible except for very low frequencies. But I was always a little uneasy about something in the theory and experimental evidence. Then I stumbled across the DEQX website (after tracking the history of the Fairlight sampling synthesizer; but that’s another story) and the possibilities of phase alignment in truly high fidelity sound reproduction.

    Funnily enough, one of my all-time favourite pieces of music depends in large part on a newly discovered (at least to the world of pop music in 1967) sound effect called flanging. The piece in question is Itchycoo Park by The Small Faces. The flanging/phasing effect (see Wiki) derives from two originally identical signals that are mixed together with a time varying phase shift or delay between them. Even tiny phase shifts produce pronounced sound effects.

    Thank you again for challenging my complacency and inspiring me to find out more.

    Like

  2. Hi Kieran. Many thanks for your very interesting comment.

    Yes, when I was in my late teens the Fairlight CMI was a true object of desire for me, and even now when I see them on old editions of Top of the Pops or whatever, they still look like the future!

    I concur with you about the Small Faces, too. Definitely one of my all-time favourite bands. One of those bands that were ‘even better than they needed to be’.

    Like

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