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the oster-curve

Understanding The Oster Curve

The Oster Curve was developed by Dr. Gerald Oster, who pioneered binaural beats research in the 70s. He proposed how they might be used as a diagnostic tool for purposes related to health and science.

As we explain in our article here, Dr. Oster didn't invent binaural beats, or propose their use for brainwave entrainment; that came later. What he did summarize was the following:

The fact that sub- threshold sounds are effectively rendered audible by binaural beats suggests that there may be other stimuli processed by the brain of which we are not aware. Finally, it is possible that hormonally induced physiological or behavioral changes too subtle to detect by ordinary means may be made apparent by measuring the binaural beat spectrum.

Considering the above, what Dr. Oster did was open up people's minds to the fact that the natural phenomenon of binaural beats demonstrates to us that there may be other stimuli (other energy, awareness, higher consciousness) affecting the body that we aren't aware of.

He published his research in a famous paper called “Auditory Beats in the Brain” (Scientific American, 1973).

Part of his research included the ‘Oster Curve', which  is essentially a graph that shows which carrier frequency is optimal to hear binaural beats at specific frequencies. For example, the Curve recommends that Theta binaural beats should use a carrier frequency in the 160–210 Hz range.

But! We should note at this point that we can't take the Oster Curve as a literal guide to the best carrier frequency to use for optimal brainwave entrainment (using binaural beats).

Why? Because that is not what Oster was researching when he developed the Curve. He was concerned with level of perception, not optimal entrainment.

However, the Curve is a useful tool because it gives us a template from which to find where the optimal carrier frequency range is for a given frequency will be.

the oster-curve

Understanding Carrier Frequencies

With that in mind, let's carry on and first define a carrier frequency.

Let's go back to basics for a moment: To create a binaural beat we need two frequencies, a left and a right frequency. One frequency is sent to the left ear, and the other to the right ear.

If we are in entraining the brain to 5 Hertz (Hz), both frequencies, the left and the right, are essentially carrier frequencies –  because they are “carrying the signal”.

But it may be the case that we start off entraining the brain to 5 Hz, and then increase this to 7 Hz after 10 or 15 minutes.

In this situation, one of the frequencies, the left or the right, will need to change. The frequency that doesn't change, then becomes the sole carrier frequency, and ultimately what is referred to as “the carrier frequency”.

By nature of the way this works, the carrier frequency is usually the lower of the two frequencies.

To better illustrate this point, let's refer to our example of 5 Hz.

If we set the left ear frequency at 200 Hz, and the right ear frequency at 205 Hz, the brain is entraining to the mathematical difference between these two numbers, which is 5 Hz.

We would identify the left frequency as the carrier frequency, because this is essentially our starting point.

If we want to increase the entrainment to 7 Hz, then we increase the right frequency to 207 Hz. The left frequency remains constant. The left ear is hearing our carrier frequency.

So if we look at the table below, we can see that according to the Curve, the optimal carrier frequency for entrainment at around 10 Hz  is somewhere between 230 and 240 Hz.

As noted previously, the Oster Curve cannot be considered a definitive list of carrier frequencies that should be religiously observed, because Dr Gerald Oster's  research was not focused upon using binaural beats for brainwave entrainment.

However, subsequent research shows that the Curve is fairly accurate for the purpose of entrainment.

We know this because of controlled studies, like this one. This study used Theta waves to induce a meditative state at a carrier frequency of 250 Hz to entrain to 6 Hz.

This study produced very good results, despite the Curve stipulating a frequency of  200 Hz for a 6 Hz signal and the study using one of 250 Hz.

Still, it is not far off the mark, and indeed from studies such as this we can make the assumption that Theta and Alpha entrainment will be effective within a carrier frequency between 180-250 Hz.

That said, research is ongoing, and over time both individual sound enthusiasts and scientific research continue to report specific frequencies of entrainment being very effective at specific carrier frequencies.

However, it is not something we should obsess over, because we have good evidence that working within a particular range for each brainwave category entrainment should still be effective for most people.

What is more likely to affect a person's perception of binaural beats and their ability to be affected by them are other things noted by Dr Gerald Oster in his paper such as the point in time a woman is at during her menstrual cycle, as it appears that Estrogen and has an effect on audible perception.

The Oster Curve (Oster's Curve)

Optimal Carrier Frequency (Hz)Beat Frequency (Hz)
100.235
200.444
300.615
400.768
500.964
601.21
701.451
801.659
901.856
1002.054
1102.265
1202.581
1302.903
1403.266
1503.669
1604.073
1704.596
1805.104
1905.835
2006.821
2107.66
2208.599
2309.551
24010.604
25012.037
26013.935
27015.396
28017.023
29018.571
30019.453
31020.815
32021.767
33022.41
34023.248
35023.843
36024.459
37024.813
38025.14
39025.604
40025.771
41026.026
42026.103
43026.185
44026.232
45026.249
46026.25
47026.108
48025.775
49025.566
50025.41
51025.083
52024.688
53024.257
54023.836
55023.393
56022.993
57022.387
58021.466
59020.535
60019.513
61018.116
62017.206
63016.295
64015.479
65014.836
66014.087
67013.155
68012.58
69011.896
70011.21
71010.61
72010.029
7309.492
7408.722
7508.364
7608.059
7707.703
7807.318
7907.002
8006.661
8106.356
8206.116
8305.881
8405.642
8505.44
8605.28
8705.138
8804.846
8904.703
9004.565
9104.396
9204.203
9304.053
9403.894
9503.744
9603.623
9703.514
9803.391
9903.274
10003.161
10103.015
10202.855
10302.697
10402.576
10502.46
10602.347
10702.236
10802.124
10902.011
11001.896
11101.775
11201.644
11301.523
11401.428
11501.354
11601.283
11701.199
11801.109
11901.021
12000.974
12100.968
12200.924
12300.85
12400.762
12500.666
12600.575
12700.555
12800.562
12900.536
13000.498
13100.453
13200.406
13300.372
13400.37

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