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)
10 0.235
20 0.444
30 0.615
40 0.768
50 0.964
60 1.21
70 1.451
80 1.659
90 1.856
100 2.054
110 2.265
120 2.581
130 2.903
140 3.266
150 3.669
160 4.073
170 4.596
180 5.104
190 5.835
200 6.821
210 7.66
220 8.599
230 9.551
240 10.604
250 12.037
260 13.935
270 15.396
280 17.023
290 18.571
300 19.453
310 20.815
320 21.767
330 22.41
340 23.248
350 23.843
360 24.459
370 24.813
380 25.14
390 25.604
400 25.771
410 26.026
420 26.103
430 26.185
440 26.232
450 26.249
460 26.25
470 26.108
480 25.775
490 25.566
500 25.41
510 25.083
520 24.688
530 24.257
540 23.836
550 23.393
560 22.993
570 22.387
580 21.466
590 20.535
600 19.513
610 18.116
620 17.206
630 16.295
640 15.479
650 14.836
660 14.087
670 13.155
680 12.58
690 11.896
700 11.21
710 10.61
720 10.029
730 9.492
740 8.722
750 8.364
760 8.059
770 7.703
780 7.318
790 7.002
800 6.661
810 6.356
820 6.116
830 5.881
840 5.642
850 5.44
860 5.28
870 5.138
880 4.846
890 4.703
900 4.565
910 4.396
920 4.203
930 4.053
940 3.894
950 3.744
960 3.623
970 3.514
980 3.391
990 3.274
1000 3.161
1010 3.015
1020 2.855
1030 2.697
1040 2.576
1050 2.46
1060 2.347
1070 2.236
1080 2.124
1090 2.011
1100 1.896
1110 1.775
1120 1.644
1130 1.523
1140 1.428
1150 1.354
1160 1.283
1170 1.199
1180 1.109
1190 1.021
1200 0.974
1210 0.968
1220 0.924
1230 0.85
1240 0.762
1250 0.666
1260 0.575
1270 0.555
1280 0.562
1290 0.536
1300 0.498
1310 0.453
1320 0.406
1330 0.372
1340 0.37
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