Carrier frequencies, explained

When Sonor plays an isochronic tone, two different numbers are at work. The beat frequency is how many times a second the tone switches on and off, and that rate is what sets the brain wave band. The carrier frequency is something else: it's the pitch of the tone itself, the note you actually hear. Changing the carrier changes how the tone sounds. It does not change the brain wave band; only the beat does that.

Why a carrier is needed

Slow beat rates, such as 4 or 10 times a second, are too slow to hear as a pitch on their own. So an audible tone carries the pulse, and that tone switches on and off at whichever beat rate you pick.

What Sonor offers

A slider runs from 60 to 170 Hz in 10 Hz steps: low on this range sounds like a soft hum that sits easily under music, high sounds like a clearer note. Alongside the slider is a set of fixed higher values: 174 Hz, 285 Hz, 396 Hz, 417 Hz, 432 Hz, 528 Hz, 639 Hz, 741 Hz, 852 Hz, 963 Hz, 1111 Hz. Nine of those are solfeggio values; see What are solfeggio tones? for where that set comes from. The carrier is independent of the pulse itself; see What are isochronic tones? for how the beat and the bands work.

What the research says

In one brain recording study, researchers measured the brain's own following response to a 40 Hz pulse carried on tones of different pitches. The response was larger at lower carrier pitches, about three times larger at 250 Hz than at 4000 Hz (source 1). The lowest carrier in that study was 250 Hz. No study located measured a response across the 60 to 170 Hz range of the slider. That is a measured response, not proof of a changed state of mind. No research shows that any one carrier pitch is better for focus, calm or sleep.

How to choose

Choose a carrier by comfort. A lower carrier sits further under your music and is easier to ignore; a higher carrier is easier to hear on small speakers. Phone and laptop speakers reproduce very low tones poorly, so go higher or use headphones if you can't hear it. Keep it quiet.

This isn't medical advice. Pulsing audio can affect people with epilepsy or a seizure disorder, so check with a doctor before using it if that applies to you.

Sources

1. Ross B, Draganova R, Picton TW, Pantev C. Frequency specificity of 40-Hz auditory steady-state responses. Hear Res 2003;186(1-2):57-68.
   The brain's response to a 40 Hz pulse shrank as the carrier pitch rose; at 250 Hz it was about three times larger than at 4000 Hz.
2. Picton TW, John MS, Dimitrijevic A, Purcell D. Human auditory steady-state responses. Int J Audiol 2003;42(4):177-219.
   The brain's response follows a sound that pulses at a steady rate, strongest near 40 Hz; this is a measured response, not proof of a changed state of mind.