Audible Illusions

Discussion in 'Speakers & Subwoofers' started by Chu Gai, Jul 12, 2004.

  1. Chu Gai

    Chu Gai Lead Actor

    Jun 29, 2001
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    Recently, at a different forum, mention was made of the capacity for the human brain to fill in information with regards to our blind spot in order to obtain a complete picture. That our eyes can play tricks on us, distorting reality, is fairly easy for the majority of us to understand and accept. Early in our education and exposure to 'brain teasers' we were shown such things as mirages, the apparent separation of a straw in a clear glass filled with water, length of lines being the same when they are not, that a fish or an object is not necessarily where we think it is when looked at from the surface, the artistic style exemplified in the pointilism technique, etc.

    Such exposure to the falsification of our senses is lacking with respect to hearing though. In that posting, mention was made by myself that this ability or defect or characteristic also extends to the human auditory process. Some, perhaps due to a misunderstanding upon their part or for self serving reasons, take this to mean that a Walmart stereo system is sonically indistinguishable from your system in your home or that a Bose 901's sound the same as say ML's. Such statements and extrapolations do nothing to further our understanding of how hearing works. Further, the validity of careful work that is repeatable and verifiable across the globe, should not be underestimated even when it runs contrary to what we perceive as our own experiences. No doubt it is difficult for us to come to grips with such findings and many will continue to hold onto a false belief even when presented with overwhelming scientific evidence to the contrary. To simply dismiss such findings without doing more digging can cause us to continue chasing our own tails advancing nothing other than someone else's agenda. Being that I tend to look at people and society in some sense as statistical distributions, I rather suspect this tail chasing will go on even if humanity is so fortunate as to one day travel to other stars. Isaac Asimov and the Foundation series of novels and all that.

    Dr. Diana Deutch is an active researcher and has published expensively on audio illusions. For example, in the article titled Musical Illusions found in the 1975/10 issue of Scientific American, Deutsch examined the presentation of binaural tones to various listeners. For example, consider the following sequence:

    right ear: c2 d1 a1 f1 f1 a1 d1 c2
    left ear: c1 b1 e1 g1 g1 e1 b1 c1

    One would expect, based on the often stated "Trust Your Ears", that listeners, especially trained listeners, musicians if you will, would report the correct tones in the correct ear. However, in virtually every instance, the perception of the listener was very much different.

    right ear: c2 b1 a1 g1 g1 a1 b1 c2
    left ear: c1 d1 e1 f1 f1 e1 d1 c1

    It's important to note that the notes, d1, f1, etc. did not physically exist in the left ear at all yet they were perceived as being there. Similar 'error's of delusion also existed in the right ear.

    Further examples of Deutsch's work can be found here:
    One may also purchase a CD for about $15 plus the usual s/h where she illustrates a variety of audible illusions.

    Deutsch has also studied a number of other interesting phenomena such as perfect pitch and an interesting synopsis of that can be found here:

    It's of some interest to note that there is not a uniformity amongst people to perceive illusions the same. In the link,, we see on the sidebar, that Californians have a decidedly different response to the Tritone Paradox as opposed to Brits. This link also indicates that audible illusions, while not understood years ago, were nonetheless exploited by composers. Perhaps some will take it upon themselves to look for various performances of Tchaikovsky's Pathétique.

    Another example of the human brain hearing things that are not there can be found in Bach's Sonata for the Unaccompanied Violin #4. The piece is performed on an instrument that is completely not capable of producing multi voice music, yet when one listens to it, one hears three voices and four-note chords. Examination of the waveforms by oscilloscopes confirms that there are no chords yet they are almost universally perceived as being there.

    It's not a comfortable thing for us when terms such as delusion are used to describe something we've experienced. Nor are words such as ignorant. The words brings out decidedly negative connotations suggesting that perhaps the individual should be institutionalized or that they are somehow an idiot. There is much though that we're unaware of simply because we haven't been exposed to it at perhaps an early enough age so that it becomes fun and non-confrontational. Hopefully the references cited will cause some of us to dig a bit deeper and come to understand that hearing and listening is a fairly complex topic and that those who understand this can and will exploit our ignorance of the matter not to serve our best interests but theirs. There is illusion and there is delusion. Let us understand there is a difference between the two and not be so quick to dismiss careful work.

    That's my 2.83 volts worth.
  2. ChrisBee

    ChrisBee Stunt Coordinator

    Mar 4, 2004
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    Interesting post. [​IMG]

    I am quite prepared to accept the idea of aural illusion & particularly spatial illusions. Stereo is a perfect example.

    I regularly hear sounds well outside my stereo speakers. Sometimes low frequency sounds are heard well beyond the left speaker when the subwoofer is actually on the right. Though not all the time. Which is a shame because I could save the cost of investing in a high quality surround sound stystem. [​IMG]

    There are many strange aural illusions. For example: The feeling that slow wavefronts are crossing the listening room. I cannot imagine these are actually real. Yet they occur now and then at high levels of low frequency sound. Probably @ 30Hz and below. Usually when watching films in stereo sound with a large subwoofer and floorstanding speakers at fairly high levels ~90dB+. I noticed this effect only last night on one scene of LOTR3 at quite moderate levels. I just hope I'm not unique in sensing this effect! :b

  3. mark alan

    mark alan Supporting Actor

    Nov 19, 2002
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    If you are interested in audio illusions, there are a couple of programs you should download, the Brainwave Generator or the Neural Noise Synthesizer. They do some really cool things with sound. They are intended to capture and control your brainwave frequencies. For example, if you play a 400 hz note in your left ear and a 410 hz note in your right ear, your brain will hear a 10 hz note. If done properly, your brainwaves should adjust to that frequency.

    There are some really cool other effects, such as an ocean effect where the sound seems to move from one side of your head to the other. It is really wild.

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