Moulton Laboratories

the art and science of sound

The Microphone vs. the Ear

Dave Moulton

May 1993

1. The Problem

2. Overview

3. Comparing Ear and Mic

4. Sound Localization

5. More Ear Tricks

6. What does it mean?

Comments (5)

Why Recordings Don't Sound Quite Like the Real Thing and Some Things You Can Do About It. An informal introduction to the realities of psychoacoustics.

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Sound Localization

Another important issue has to do with localization -- the ability to discriminate which direction a sound is coming from. The microphone can't detect this at all, while the ear does in several interactive and highly complex ways. As sound enters the outer ear, tiny reflections of the sound bouncing off the pinna (the flap of skin surrounding the ear canal) recombine with the direct signal to create very complex and distinctive interference patterns (comb filtering in the range between 5 and 15 KHz.). Each different angle of arrival of a sound yields its own distinctive and audible pattern, and the brain uses these (actually it happens at the basilar membrane and in the auditory nerve on the way to the brain) to determine which direction any sound element is coming from, from each individual ear.

Also, as you probably know, the differences in sound amplitude and time between the two ears are also used to help localize the sound in space. Sound from any given point in space will have a slightly different time of arrival, spectrum and amplitude at each ear, and these differences are integrated, in the same way that our binocular vision gives us depth perceptions, into a spatial image in which the sound source is localized at some distance and direction away from us.

On the other hand, the microphone can only detect an amalgam of all the sounds arriving from all different directions. Some directional microphone designs (like cardioid and bi-directional) in effect turn down the volume of some sounds coming from some directions, but they have no way to actually discriminate the direction of the arrival of a given sound: from the left, or up, or in back, etc., while a single ear is able to localize the angle of arrival of a sound. If you don't believe this, cover one ear up and try to localize sound sources with the other. You'll find it's no particular problem, although not quite as easy or comprehensive as with both ears. The most important issue about all this is that this localization ability allows us to differentiate sounds we want to hear from background noise, which is something a microphone simply cannot do. This turns out to be a major source of difficulty when recording in a reverberant space. We can sort out the difference between the sound we wish to hear and the ambience -- the microphone cannot, so reverberant recordings tend to sound blurry.

NEXT> More Ear Tricks

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COMMENTS

Staten Island, NY Jun 10, 2006 11:36 PM

These articles are amazing, genius.... i can't wait to read all of them and then re-read all of them again... - Christopher

Christopher Sauter

USA Mar 12, 2010 03:46 AM

The article seems to miss that whether a mic/speaker or direct sound is emanating, the ear is going to be used and all its cool features and the brain processes inherent in that, unless we are talking about robots enjoying music. The comparison should instead be the sound that enters the ear in each instance. You would not want a mic to do the processing the ear does because the processing would be doubled with, no doubt, strange results.
Also, even though light moves faster than sound the brain take more, not less time to process vision. Watching the other musician instead of listening is probably not the best choice unless you can perceive the changes more clearly with vision than sound.
I also seriously doubt that we can tell what direction sound is coming from with one ear other than by moving our heads or already knowing how loud a sound should be if we were aimed at it optimally.
I have some hearing loss in one ear. If I put a hearing plug that ear, that mutes it by an additional 33DB, I am pretty close to deaf in that ear in that situation (which I have to do some times because the muscle he was talking about goes nuts sometimes). When that is the case I truly can't tell what direction sound is coming from with my good ear. My guess is that you are picking up some small bit of sound in the covered ear that is providing you with its direction. One ear direction I say is a total myth. Memory of a sound as it changes typically going around ones head may give cues we pick up, but if there is no relative movement history of the sound, I say I highly doubt any direction can be discerned.

mindbreaker

Sydney, Australia Dec 13, 2011 09:42 PM

mindbreaker is quite right; this article shows a complete misunderstanding of the way the acoustic recording/playback system works.

We would want the microphone to be similar to the ear if we were going to bypass the ear of the listener and insert electric signals directly into his nervous system, but this is, of course, not what we intend.

The role of the microphone is to capture information that is 'encoded' in air pressure fluctuations and convert it into a forma that can be stored. The loudspeaker is then called upon to convert this information back into its original form. Of course, there are many problems with this system, mostly at the loudspeaker end, but what matters at the microphone end is the completeness of the information-capture, not the exact mechanism.

Suppose, in an analogous case, that we take a page of handwriting, scan it into a computer, and then print it back into a new but almost identical page. It makes no difference that the scanner works in a totally different way from that in which the eye does, we just want it to capture as much information as possible.

Tim Smith

Groton, MA Dec 14, 2011 09:44 AM

Without spending a lot of time on this, there IS other research suggesting how single-ear localization happens. Further, I was startled by how robust I found that localization to be, even subject to its limitations. I'm not able to comment on mindbreaker's personal experience. My experience remains anecdotal, but easily, if fuzzily, repeatable. Thanks for writing, mindbreaker!

Dave Moulton

Groton, MA Dec 18, 2011 12:24 PM

Tim Smith makes some really good points in his post (although I disagree about my completely misunderstanding how acoustic recording/playback works – actually, I think I DO understand it).

Anyway, in this article I was comparing the ear to the microphone to illuminate various things about each of them, and also to show some places where we typically get confused. Tim isn't confused – he's got a really good handle on it.

The problems he doesn't get to have to do with where errors accrue in the capture of information at the microphone. We lose a lot there. Take a look at:

www.moultonlabs.com/weblog/more/we_want_really_accurate_recordings

Anyway, thanks, Tim, for an excellent and thoughtful post.

Best regards,

Dave

Dave Moulton

Sound Localization

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