Have you heard of binaural beats? (Probably, if you’re reading this).

So this Lazy Old Geek(L.O.G.) describes it as one frequency in the left ear and a different frequency in the right ear. The ears/brain/whatever combines the two to produce the difference frequency in the brain.

Here is a pretty good article on Binaural Beats:

https://www.medicalnewstoday.com/articles/320019#h...

So you might wonder why not just generate the frequencies you want and put them on a speaker?

Well, I have a reason. As said in the article the brainwaves of interest are from Delta to Gamma or 0.5Hz to 50Hz. Well if you look at the specifications for most speakers/headphones/earbuds, they do not go that low.

So do they work? Well, I don’t know, here’s a couple of studies that suggest they might and might not.

TIP: I don’t know about you but I’m too Old to really understand these ‘scientific studies’ but sometimes I pick out a statement of interest.

https://onlinelibrary.wiley.com/doi/full/10.1111/j...

“This study suggests that offering binaural beat audio before day case procedures might serve to bring about anxiolysis ((a good thing)) in the majority of patients without impacting adversely on postoperative functioning.”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC56948...

Binaural Beat: A Failure to Enhance EEG Power and Emotional Arousal ((but this suggests a failure for very limited situations)

On the commercial side, there are a lot of companies that claim to produce binaural beats music. Here’s some free Binaural Beats:

https://medium.com/syndicate-post/7-of-the-best-bi...

What do I think? There are some studies that suggest Binaural Beats can help improve sleep quality. Well, I’d like to do some experimenting with binaural beats and maybe do some non-scientific studies, so I’ve developed my own binaural beats generator.

Step 1: My Binaural Beats Generator

It looks like a jumble of wires and parts but this is Phase 1. The little blue item, upper left is a 3.5mm jack for earbuds. The two PCBs middle right are AD9833 signal generators. The metal shaft at the bottom is the volume control.

Design: Output two sinewaves of slightly different frequencies to some earbuds. This is a very basic Binaural Beats Generator.

Parts:

3.3V Micro Pro Arduino

2 AD9833 DDS signal generators

Dual 10k potentiometer

3.5mm audio jack

Earbuds (Sennheiser MX400)

All parts except the earbuds were purchased from AliExpress.com.

Design Concept: The AD9833s can generate sine waves of various frequencies. The 3.3V Arduino Micro Pro sets the AD9833s frequencies (and shape - sine wave). The potentiometer controls the volume. The outputs from the AD9833s are connected to the audio jack. The earbuds are plugged into the jack.

Concerns: When I designed the circuit, I didn’t know if the AD9833s would drive the earbuds. I breadboarded the circuit and found out they were actually too loud so I added the dual ganged potentiometer.

I measured the resistance of the earbuds, they were 32 Ohms (which I think is called their impedance). By the way, I tried a different set of earbuds which I think measured 15 Ohms, they were pretty quiet.

Schematic is attached.

Software: I think there are a few Arduino libraries for the AD9833. I chose this one:

https://github.com/Billwilliams1952/AD9833-Library...

I modified the ApplySignal.ino example for two AD9833s and saved it as:

BB1.ino

This is a very basic program, in an editor just change the numbers 245 and 248 in these statements to whatever frequencies you want in the Left and Right channels.

genL.ApplySignal(SINE_WAVE,REG0,245);

genR.ApplySignal(SINE_WAVE,REG0,248);

FYI: they can be decimal numbers like 244.98.

The next picture shows that my Owon oscilloscope shows frequencies of 245.1Hz and 248.1Hz. So it looks and it sounds like its working. To me it sounds like a steady tone with a warble in it.

BB_Adjust.ino

This is a sketch I wrote where I can change the frequencies using serial communications (on the fly) without having to reload the sketch. The serial monitor displays the actual frequencies generated by the AD9833 along with what frequency you asked for (They are not quite the same). Plus it shows the difference(Beat) frequency. See picture.

So this seem to work pretty good. I will probably do some testing with various frequencies and beats to see if I can see any affects on my EEG in this Instructable:

https://www.instructables.com/id/EEG-AD8232-Phase-...

What is supposed to happen is the brain will synchronize with the binaural beats frequency. This is called Brainwave Entrainment:

https://omnipemf.com/brainwave-entrainment-what-is...