Understanding Binaural Beats

Whenever a new discovery or technology is adopted by the New Age marketing machine, it can change from being basically useful into a miracle cure sent to us by aliens, supreme beings, or the 9th sun god of the Aztec empire ( currently being channeled by Jerry Springer). The truth is mixed with huge doses of unsubstantiated claims, unrealistic promises and outright lies. It is easier to bend the truth with the New Age consumer, because they have a stronger desire for the fantastic to be real. Binaural beats is being subjected to the same suspicious marketing tactics. What is simply a curious auditory hallucination is now the basis of a large and lucrative industry that sell "enhanced" meditation music that is claimed to directly affect and alter your brain waves.

Binaural beats is an interesting phenomenon of the human auditory system. If you play two different tones that are very close together in pitch, separately into the the left and right ears, a single, pulsating sound is heard. This article will look more closely at how this works and explain the process in detail.

The phenomenon of binaural beats is easily demonstrated and fairly well studied and researched, but the step taken from provable to questionable is that binaural beats can directly affect and alter your brainwaves. The claim being made is that the pulsing sound heard when listening to a binaural beat will resonate with the rest of the brain, and force the brainwaves to follow this same frequency. This is the brainwave-synchronization process known as "entrainment" or "frequency following response".

I need to make it clear now that I'm not explicitly saying that it doesn't happen, or that binaural beats definitely don't affect brainwaves. I'm trying to show that there is not enough evidence that it definitely does happen. Given the propensity for New Age consumers to believe in angels, faeries, aliens and tachyon filters, the leap of faith required for believing that binaural beats can affect your brainwaves is quite small. Which is possibly why the phenomenon is so easily exploitable -- from promising that "Now you can Meditate Deeper than a Zen Monk...INSTANTLY!" to helping you grow taller. Yep, really: Grow taller with binaural beats. For the most part, binaural beats are used to assist in meditation and are added into music or ambient sound tracks to help the listener reach a specific mental state.

History

The consensus seems to be that Heinrich Wilhelm Dove discovered binaural beats in 1839. Pretty much nothing more happened until Scientific American published a paper by Dr Gerald Oster in 1973. That's about much as I could dig up on actual history. Most of the development on the concept has been done specifically for binaural beat based products.

There is not a lot of history here, as there is not a lot to binaural beats. Studies of the human auditory system have a significantly more detailed history, of which the subject of binaural beats is a very small part.

How it Works

It’s easy to demonstrate a binaural beat. In this first example, I created a file with a 200 Hz triangle wave tone in the left channel and a 205 Hz triangle wave tone in the right channel. There are a few basic wave forms used to create sounds, and the triangle wave form has some gentle harmonic content that helps emphasize the binaural beats. (If you are not familiar with sound generation principles, here is a great resource to learn about it). I have added a little bit of filtered white noise to make the binaural beat more perceptible.

Note: The demo is in mp3 format, but is compressed at the highest bit rate possible (320kpbs). The sound is simple enough that no significant data is being lost. The audio examples here need to be listened to on headphones, not PC speakers. Right-click the link and click "Save As.." to save any of the sound files on this page.

Example 1: binaural-tri-noise.mp3 (right-click on the link and click "Save As.." to save the file)

Figure 1.

Figure 1 is a visual representation of Example 1. As you can see by the yellow lines, the left-hand channel is oscillating at a slower rate than the right-hand channel.

Example 1 uses triangle waves, as it is easier to hear the separate tones. However, binaural beats are most often made using sine waves, which are are sometimes referred to as pure tones. Using sine waves makes it slightly harder to hear the tones, but the binaural beat can still be heard. Example 2 uses sine waves to create the sound, and you can see the difference in Figure 2.

Example 2: binaural-sine-clean.mp3 (right-click on the link and click "Save As.." to save the file)

Figure 2.

To understand the brain mechanism that produces the binaural beats, it’s necessary to cover some fundamentals first: sound waves, the human auditory system and sound localisation.

Sound Waves

Whenever you hear any sound, the “sound” has travelled as a sound wave through the air, from the source of the sound and into your ears.To better understand the notion of sound and sound waves, it’s easiest to start with an example we are all generally familiar with, the hi-fi speaker.

Figure 3 and 4.

A loudspeaker’s basic components are a magnet, and a coil attached to a flexible cone known as the diaphragm (see Figure 4).

Figure 5.

Passing an electrical signal through the coil causes the cone to move. Depending on the direction of flow of the current, the cone either moves towards, or away from, the magnet, as shown in Figure 5. (This is the same physical principle at work in an electric motor.) The electrical signal coming into the HiFi speaker causes the diaphragm to move back and forth very quickly, somewhere between 20 and 20,000 times per second. As the diaphragm moves in and out, it compacts and expands the air that it touches.

Figure 6.

Figure 6 shows how the air around a speaker is affected but a moving diaphragm. In 6a, the diaphragm is at rest and the air around the speaker is also at rest, represented by the grey curved lines. When the diaphragm is brought forward (6b), the air near the speaker is compressed (the darker lines). This compressed air is the beginning of a sound wave that starts to move away from the speaker. In part c, the diaphragm moves backwards and there is an expansion of the air (the lighter lines) which follows behind the compression part of the wave as it moves away from the speaker. When the speaker is finally at rest again in part d, the sound wave is moving farther away from the speaker and into the surrounding air.

What is important to note is that the air doesn't actually move like wind; it compresses and then expands to let that wave pass through. Think of a long, stretched-out Slinky spring. If you push the Slinky on one end and stretch it back, a compression wave will travel along the Slinky, but the Slinky itself still stays in the same place.

Compression and expansion of air as illustrated in Figure 6 shows that sound waves are simply vibrating air. There are other ways to cause air to vibrate and produce sound waves: tapping on a keyboard, passing air over vocal chords, or plucking a string on a guitar. All the sounds you hear have come from a source that has caused the surrounding air to vibrate.

A sound wave is often represented visually as a transverse wave. The wave crests and troughs represent the compression and expansion of the air. The electrical signal used to generate the sound will have the same transverse waveform. Figure 7 shows how the rising and falling of the transverse wave corresponds to the compression and expansion of the air from a sound wave.

Figure 7.

If you would like to find out more about sound waves there are some YouTube videos (here and here) that take the concept a bit further.

Auditory System

The auditory system is an amazingly complicated biological marvel that lets our brains perceive and comprehend the thousands of sound waves that bombard our ears throughout the day. Our brains continuously receive and interpret nerve impulses from our various senses, and the auditory system converts the sound waves that come into the ear into nerve impulses for our brains to understand. Its almost as if the sound is digitised as it moves through the ear.

Figure 8.

Understanding the human auditory system is a very long and complicated topic. For the purposes of this article, though, it is important to know that the sound that arrives at our ears is converted into nerve impulses. The brain must interpret these nerve impulses in order for us to "hear" the sound. By interpreting the sound waves, we can derive information (such as pitch, volume, and timbre) and also locate where the sound is coming from. Beyond the immediate perception of sound, we also use these nerve impulses to recognise speech and appreciate music.

Sound Localisation

Sound localisation referrers to the process that allows us determine the source of a sound, using our auditory system. You can hear when someone is talking behind you, or an aeroplane flying over your head, or someone hoots at you. Our brains are pretty good at using the information coming into our ears to work out where a sound has come from. Its goes further than that, though, as the brain actually tries to project where the sound has come from, in a kind of 3D audio field. For example: When you listen to music on headphones, it sounds like the music is inside your head. But when you listen to HiFi speakers, the sound appears to originate at the speakers themselves.

Sound localisation as a science is fairly well documented, and the process seems reasonably well understood.

The brain uses one of three mechanisms to locate where a sound came from:

1 - Inter-aural Intensity Difference (IID)

IID refers to the difference in volume or sound levels that are heard at each ear. If sound originates at your left, your head acts as a barrier or filter and reduces the level of sound heard in the right ear. This difference in the levels between the two ears helps the brain work out that the sound came from the left. However, your head will only start to effectively filter sound where the frequency of the vibration is above 500 cycles per second (also known as Hertz or Hz). In Example 3, the left side is louder than the right side. Listen to how the sound appears to be coming from the left.

Example 3: binaural-IID.mp3 (right-click on the link and click "Save As.." to save the file)

Figure 9.

2 – Inter-aural Time Difference (ITD)

ITD is the mechanism relevant for understanding binaural beats. As a sound wave travels through the air, it is a progression of compressions and expansions of the surrounding air. The sound wave travels through the air at the speed of sound, which is approximately 350 meters per second (or 1238 km/h). A sound source to the left of your head will produce a wave that moves from your left ear to your right ear.

Figure 10.

Figure 10 shows that a sound wave moving through the air can present a compression part of the wave at one ear and an expansion part of the wave at the other ear. Both ears are still hearing the same sound, but at fractionally different times (0.63 ms apart, to be more precise). This is also known a “phase” difference.

Your brain can not only detect this fractional time difference, but also use it to work out where the sound originated. Exactly how the brain figures this out is one of the marvels of our auditory systems that is not fully understood, but it clearly does do it. Example 4 illustrates this point. Here, the right channel has been fractionally delayed, and the sound appears to be coming from the left (or the other way round, if your headphones are on backwards).

Example 4: binaural-ITD.mp3 (right-click on the link and click "Save As.." to save the file)

Figure 11.

It may be a bit strange to hear the ITD demo without hearing what the original should sound like. So this next example is the same 200 Hz tone in each ear, without the tiny time difference.

Example 5: binaural-ITD-none.mp3 (right-click on the link and click "Save As.." to save the file)

ITD only works for sounds where the frequency of the vibration is less than 1000 Hz. Above that frequency, the sound wave is vibrating too quickly for the brain to detect a delay

3 – Head-Related Transfer Function (HRTD)

The final mechanism is more complex and has to do with the shape of the ear and the head. Sounds are filtered differently depending on the angle at which they travel toward the ear. A sound you hear above you will sound different from the same sound produced directly in front of you. Its an interesting topic, but not necessarily relevant to binaural beats. There is an excellent article that covers this and more available here.

The Binaural Beat Hallucination

Now that we know how sound waves, the auditory system and sound localisation all work together, we can look at binaural beats. From here on out it’s just a theory, though, as it’s currently not possible to prove this conclusively. When we listen to binaural beats, we are hearing what seems to be a single tone that has a subtle pulsating quality, rather than separate tones in the left and right ears.

If you played the same separate tones on your HiFi, you would also hear a pulsing beat. Example 6 was recorded using a microphone placed between the speakers in my studio. You can still hear the beat, but it sounds different from the binaural beat you hear with the original recording using headphones. This easy explained as interference.

When played through HiFi speakers, the sound waves interfere with each other, and through constructive and destructive interference will cause the sound waves to pulse. It is as if you have added the left and right channels together to produce a third result that contains the pulses. Figure 12 shows what the sound recorded with the microphone in the studio looks like. I’ts zoomed out more than the other images to show what the pulse looks like.

Example 6: binaural-mic-record.mp3 (right-click on the link and click "Save As.." to save the file)

Figure 12.

If you’re using headphones, it is not possible for the sound waves to interfere with each other. The sound-pressure levels of headphones are so low that the sound waves can not travel through or around your head. Example 7 has the same frequency tones for the left and right channels, but the left channel has been flipped to be the inverse of the right channel.

Example 7: binaural-inverted.mp3 (right-click on the link and click "Save As.." to save the file)

Figure 13.

If interference was present when you used headphones, the sound should be a lot softer, almost non-existent, compared to any of the others. Therefore, the binaural beats we hear with the original track cannot be produced by interference.

Binaural beats are an auditory hallucination that occurs while the brain is trying to determine where the sound is located. When the two tones are close enough in pitch, the brain does not hear them as two distinct sounds. Rather, it is trying to interpret what it is hearing as one single sound that arrived at both ears. Since the tones are at a different pitch to each other, the compression and expansion of the air from the sound waves will arrive at different times at each ear.

Normally, when the same sound arrives at different times at the ears, the brain uses this information to determine where the sound has come from. With binaural beats, the time difference the brain perceives is continuously changing, and the gap between the successive compression and expansion parts of the sound wave is different for tones of different pitch. A binaural beat appears as a continuously moving target for your brain, as it tries to work out where the sound is coming from. The pulsing that you hear is a hallucination as your brain is continuously trying to place the where the sound is coming from, and keeps having to move it. If you listen very closely to the binaural beat, you get a sense that it is quite wide, and not in the middle of your head, like the microphone-recording example.

The limits within which binaural beats work help support this theory. Binaural beats only work when the frequency of the tones is below 1000 Hz, which is the same for Inter-aural Time Difference (ITD), as explained earlier. Example 8 has the two tones at 3000 Hz and 3005 Hz.

Example 8: binaural-3000Hz-tones.mp3 (right-click on the link and click "Save As.." to save the file)

Binaural beats also don’t work if the difference in frequency between the two tones is more than 30 Hz, as your brain will then perceive two separate sounds, and will not try to combine it into one sound. In example 9, the two tones are at 200 and 250 Hz.

Example 9: binaural-50Hz-separation.mp3 (right-click on the link and click "Save As.." to save the file)

Brainwaves

Our brains have electrically active neurons that form part of the overall brain physiology. We can measure this electrical activity using a device called an electroencephalograph (EEG), which can measure the average frequency of brain activities. This electrical activity is referred to as brainwaves. The average frequency of brainwaves is associated with different states of consciousness.

• Delta 0 - 4 Hz: Deep sleep
• Theta 4 - 8 Hz: Light sleep or drowsiness.
• Alpha 8 - 12 Hz: Relaxed, alert state of consciousness.
• Beta 12 Hz and up: Active, busy or anxious thinking and active concentration.

When you are sitting relaxed or meditating, the frequency of your brainwave activity is predominantly in the Alpha range. Spending time with a relaxed brain is considered beneficial in reducing stress.

Now here comes the nub of the whole issue: Does listening to sounds and music that contain binaural beats force the frequency of brainwave activity to change? The theory is that listening to a binaural beat of 10 Hz will force the frequency of activity in the brain to change to match that binaural beat, through a process called entrainment. The conclusion is that binaural beats can change your state of consciousness from Beta to Alpha.

The problem is that there is no real proof or evidence that this is what happens. There have been studies indicating this, but they are not independent, verifiable studies that have gone through a solid peer review process. It may seem reasonable, but it has just not been proven.

The Binaural Beat Market

There are several companies that sell CDs that incorporate binaural beats. Other companies have retreats and programs you can attend that use binaural beats to help the listener reach an Alpha state of consciousness. The biggest proponents seem to be:

• Immrama Institute
• Centerpointe
• Monroe Institute
• Center for Neuroacoustic Research
• I-Doser

There are others who use binaural beats as almost a voodoo magic charm to cure what ills you:

• Get wasted on digital drugs
• Grow taller

What most of these companies have in common is that they go to great lengths to try to prove to you that binaural beats work. Clearly, if there were any real reason to trust in the efficacy of their products, they would not need to make this kind of effort. Since I first started to look into this phenomenon two years ago, it has grown considerably, and it’s a fiercely contested marketplace now on the Internet.

I don’t believe that what these companies are doing is really wrong. It is only marketing, after all, and their manipulation of the truth is no worse than anyone else’s. Besides, the people who buy these products have the right to do their own research and figure out if what the advertising says is valid or not.

Someone may eventually prove that binaural beats do change your brainwaves, or prove that they don’t. We do know that taking the time to listen to relaxing music and to try and calm you mind is a good thing.

Other References to Binaural Beats:

1 http://www.borderlands.com/archives/arch/elf.htm

2 http://www.web-us.com/thescience.htm

3 http://www.bwgen.com/fact_or_fiction.htm

4 http://peyote.com/jonstef/brain.htm

5 http://en.wikipedia.org/wiki/Binaural_beats

6 http://www.seas.upenn.edu/courses/belab/LabProjects/2001/be309f01m5.doc

7 http://www.monroeinstitute.com/