What the carrier actually does

Two numbers describe any session here, and they are constantly conflated.

• The carrier is the pitch. In this catalog, between 80 Hz and 963 Hz. It is what you hear as a note.
• The beat is how often that note pulses, or in binaural mode the difference between the ears. Between 0.05 Hz and 100 Hz. It is what the session is named for.

A "10 Hz alpha session" does not play a 10 Hz tone. Ten hertz is below the range of human hearing and no speaker would usefully reproduce it. It plays a carrier you can hear — say 200 Hz — pulsing ten times a second.

What carrier choice actually changes

Timbre, and whether you can stand it

This is the big one and the least discussed. A 108 Hz carrier is felt as much as heard — warm, close to a hum. A 432 Hz carrier is unmistakably a tone. A 900 Hz carrier is bright and, for many people, fatiguing after twenty minutes.

Since these sessions run 13 to 40 minutes, tolerance matters more than any theoretical property. The best carrier is the one you stop noticing.

Whether binaural delivery is possible

Binaural beating depends on the auditory system resolving timing differences between the ears, and that ability has measured limits: perception fails above roughly a 1 kHz carrier, and is clearest between about 400 and 500 Hz. The two tones must also stay within a few tens of hertz.

Every carrier in this catalog sits at or below 963 Hz, inside that classical limit. Where binaural is not offered, it is the beat rate above 40 Hz that rules it out, not the carrier.

Whether monaural works

Monaural sums two tones and relies on them fusing into one beating tone. Push them too far apart relative to the carrier and they separate into an audible chord instead. The guard here is 12% of the carrier — which is why a 15 Hz beat is fine on a 400 Hz carrier and impossible on an 80 Hz one.

Whether your speakers can produce it

Laptop and phone speakers roll off steeply below about 200 Hz. A 108 Hz carrier on a laptop is substantially inaudible — the modulation is intact but a good part of what you should be hearing is not being produced. This is the strongest practical argument for headphones on low-carrier sessions.

What carrier choice does not change

It does not change the entrainment target. A 10 Hz beat is a 10 Hz beat whether it rides on 108 Hz or 432 Hz.

There is a nuance: the 2025 parametric study of binaural conditions found the best attention results with a low carrier and noise masking, so carrier is not entirely neutral. But that is a modest empirical finding about one paradigm, not a rule that specific pitches carry specific properties.

For the numerology — 432 Hz, 528 Hz, the solfeggio set — see that article. Short version: they are fine carriers for ordinary physical reasons and nothing more.

Why nothing here is perfectly steady

One last detail. A perfectly fixed carrier is not ideal, because nervous systems stop responding to anything perfectly unchanging — for an unwavering tone, in roughly fifteen to twenty minutes.

So every session carries a deliberate micro-instability of about 0.1%: a 200 Hz carrier wandering by around 0.2 Hz, far below the threshold at which you could hear it move. Two independent random walks, one on the carrier and one on the beat, drifting against each other rather than in lockstep.

Whether this meaningfully prevents habituation is a design inference rather than a measured result, and we would rather say so.