binaural-beats-using-scittle

Wikipedia

A binaural beat is an auditory illusion

For example, if a 530 Hz pure tone is presented to a subject's right ear, while a 520 Hz pure tone is presented to the subject's left ear, the listener will perceive the illusion of a third tone. The third sound is called a binaural beat, and in this example would have a perceived pitch correlating to a frequency of 10 Hz, that being the difference between the 530 Hz and 520 Hz pure tones presented to each ear.

There has developed a growing science about improvements in memory and attention tasks when listening to binaural beats.

BTW the frequency and the time of the exposure matter (i.e. before and during the task is best).

Oh yes, I certainly want more of that memory and attention.

Theta waves (5Hz) actually decrease memory task performance. So I really do not want to listen to those. I heard Andrew Huberman saying that 40Hz is the most powerful.

If you know about brain waves, you might remember 40Hz as the legendarily intriguing gamma wave.

From wikipedia article:

Gamma rhythms are correlated with large scale brain network activity and cognitive phenomena such as working memory, attention, and perceptual grouping, and can be increased in amplitude via meditation or neurostimulation.

We are really talking about cool stuff here, attention, working memory, and memory processes. Also, the Binding problem.

Hearing is cool because the neuronal neural information first goes into the brainstem and then goes up some nuclei up to the thalamus. And eventually to the temporal lobes of the cortex (the 2 arm things on the side of the brain).

This is different from the vision system where the info goes directly to the thalamus.

Quoting this paper:

Presenting two tones with a slight frequency mismatch to each ear separately creates a perception of a third tone, a binaural beat, that oscillates at the absolute difference between the tones (Oster, 1973; Moore, 2012). These beats are thought to originate subcortically in the medial nucleus of the superior olivary complex, the first nucleus in the auditory pathway to receive bilateral input (Wernick and Starr, 1968; Kuwada et al., 1979). This “illusory” third tone is lateralized between the left and right ear of the listener, making binaural beats useful for spatial sound research (Ross et al., 2014).

from the Wikipedia articles on Sound localization

The auditory system uses several cues for sound source localization, including time difference and level difference (or intensity difference) between the ears, and spectral information.

and Superior olivary complex

The superior olivary nucleus plays a number of roles in hearing. The medial superior olive (MSO) is a specialized nucleus that is believed to measure the time difference of arrival of sounds between the ears (the interaural time difference or ITD). The ITD is a major cue for determining the azimuth of sounds, i.e., localizing them on the azimuthal plane – their degree to the left or the right.

So there is sort of a clump of neurons in the brainstem that are specialized to integrate the timing information between the left and the right ear. I'm guessing those then start firing in the 40Hz frequency and that is interpreted as a third sound higher up.

You throw some energy at the brain in the right form (in this case some sound waves) and it reacts in some special way. If you put it like that, it is not surprising that some things eventually, end up doing something.

Now that the phenomenon has a name we can talk about it, similar to ASMR.

Thinking about how this was always part of how the brain works. Makes me wonder if some music composers and performers implicitly hit on this earlier, or not. I tried searching the web for

binaural beats in music

but I really get the same results mix as when I search for binaural beats.

I dint feel like opening a youtube video just to listen to some sounds. As an aspiring hacker and engineer, I just want to make my computer make some sounds that I want to listen to. So I decided to make a simple website that just makes binaural beats and nothing else.

Behold 46 lines of just get the shit done.

(ns beats)

(def binaural-beat-freq 40)
(defonce ctx (or (js/window.AudioContext.) (js/window.webkitAudioContext.)))
(def slider (js/document.getElementById "frequencyRange"))
(def display (js/document.getElementById "frequencyDisplay"))

(defn ->panner [left?]
  (let [panner (. ctx createStereoPanner)]
    (set! (.. panner -pan -value) (if left? -1 1))
    (.connect panner ctx.destination)
    panner))

(def panners
  (delay {:left (->panner true) :right (->panner false)}))

(defn update-display! [value]
  (set! (.-innerHTML display)
        (str "Base frequency: " value " Hz")))

(def get-oscillator
  (memoize
   (fn [panner]
     (let [o (ctx.createOscillator)]
       (set! (.- o type) "sine")
       (. o start)
       (. o (connect panner))
       o))))

(defn oscillate [panner hz]
  (let [o (get-oscillator panner)
        _ (set! (.. o -frequency -value) hz)])
  hz)

(defn update-app [frequency-value]
  (let [frequency-value (/ frequency-value 1000.0)]
    (-> @panners :right (oscillate (+ frequency-value binaural-beat-freq)))
    (-> @panners :left (oscillate frequency-value))
    (update-display! frequency-value)))

(defn start-app []
  (update-app (* 1000 152.74))
  (set! (.-value slider) (* 1000 152.74)))

(set! (.-update_app js/window) update-app)
(set! (.-start_app js/window) start-app)

First I think let's start making a sound in 1 ear.

I am thinking a frequency that I can hear would be nice so I search the web for human auditory frequencies

1 kHz sounds like a good first thing to try. I am figuring something inside the speech area should sound natural (turned out that was a naive assumption).

Here is a more endurable sound:

(set! (.. (@oscillators 0) -frequency -value) 200)

Playing around live at the REPL with sound is fun!

Now I am thinking, let's pick some music frequency, those are supposed to be crafted over hundreds of years to be beautiful frequencies, right?

Checking out a website. I pick D#3 / Eb3. Whatever that is.

(def a-note-freq 152.74)
(set! (.. (@oscillators 0) -frequency -value) a-note-freq)

(ns beats)

(def a-note-freq 152.74)
(def binaural-beat-freq 40)
(def oscillators (atom []))
(defonce ctx (js/window.AudioContext.))

(def panners
  {:left
   (let [left? true]
     (let [panner (. ctx createStereoPanner)]
       (set! (.. panner -pan -value) (if left? -1 1))
       (.connect panner ctx.destination)
       panner))
   :right
   (let [left? nil]
     (let [panner (. ctx createStereoPanner)]
       (set! (.. panner -pan -value) (if left? -1 1))
       (.connect panner ctx.destination)
       panner))})

(defn oscillate [panner hz]
  (let [o (ctx.createOscillator)
        _ (set! (.- o type) "sine")
        _ (set! (.. o -frequency -value) hz)]
    (. o start)
    (. o (connect panner))
    (swap! oscillators conj o)))

(-> panners :right (oscillate (+ a-note-freq binaural-beat-freq)))
(-> panners :left (oscillate a-note-freq))

lol, it works.

Every now and then there are artifacts in the sound with my headphones setup. Some are just rustling and crackling.

Others sound like some kind of metal being stretched far, far away, underwater, or in slow motion. It reminds me a bit of the Dungeon Keeper soundtrack. Dark and eerie, sort of slow mow.

Pretty sure I get the third-tone illusion. I would describe it as some kind of background or in between "airy" sound. It is supposed to seem to come from the middle of the brain. It is as if the fabric of the sound is richer. Like there is sound in more places.

I did not do much web dev in my life and making a slider was a first.

I managed to put something together, drawing inspiration from w3 schools for the Html, scittle for how to export, and stackoverflow for how to add a function to "onchange".

Made with stable-diffusion. The captions are the prompts I used.

Currently does not work on mobile. Seems like I have the opportunity for another web dev feat, then. Seems like the issue is isolated on the sound appearing because the slider value works fine (meaning that the scittle code is running fine).

Now it also works on mobile! Somebody helpfully pointed out on slack that on mac there was an error about audio refusing to play before the first touch event. I fixed that by adding a play button. But mobile still did not work, ok. After checking stackoverflow I still sort of have the idea that it has to do with user interaction events and this AudioContext. I first wanted to delay the whole audio setup until you click the button. But read that you should make a single AudioContext at the beginning.

So I try to delay the 1 other thing in the code:

(def panners
 (delay {:left (->panner true) :right (->panner false)}))

(-> @panners :right (oscillate (+ frequency-value binaural-beat-freq)))
(-> @panners :left (oscillate frequency-value))

It works, haha!