--- title: "Hemi-Sync vs Binaural Beats: Frequencies and Evidence" description: "Hemi-Sync is a layered blend of binaural beats, pink noise and voice. A 1994 patent shows 4 Hz beats. Here is how it differs and what the evidence says." url: https://shimmr.app/learn/hemi-sync/ --- - [Learn](https://shimmr.app/learn/) - [Science](https://shimmr.app/learn/science/) # Hemi-Sync vs binaural beats: what is different, which frequencies it uses and the evidence Hemi-Sync is a layered blend of binaural beats, pink noise and voice. A 1994 patent shows 4 Hz beats. Here is how it differs and what the evidence says. The Shimmr team Published Oct 22, 2026 4 min read - **What Hemi-Sync is:** an audio method named by Robert Monroe, founder of the Monroe Institute, that layers binaural beats with masking noise and often a guiding voice. - **Hemi-Sync vs binaural beats:** the sound underneath is binaural beats; Hemi-Sync adds several beats at once, pink noise and instructions, plus the claim that it brings both halves of the brain into sync. - **Frequencies:** a 1994 Monroe patent gives an example of four tones from 200 to 212 Hz that make 4 Hz binaural beats, masked with pink noise. - **Evidence:** a 1999 trial of 76 surgical patients found less painkiller use with hemispheric-synchronised sounds, but a 2023 review of 14 EEG studies found brainwave entrainment results inconsistent. - **Safety:** at a low volume it is low risk for most people; never listen while driving, and talk to a doctor first if you have epilepsy. Hear it ## What is Hemi-Sync? Hemi-Sync is an audio method that layers binaural beats, masking noise and often a guiding voice, created by Robert Monroe, an American radio executive who founded the Monroe Institute in Virginia. People searching for Hemi-Sync vs binaural beats usually want to know if it is something new or a brand on a familiar idea. The short answer: the sound underneath is binaural beats, with a lot built on top. The name stands for hemispheric synchronisation. In his [1994 patent](https://patents.google.com/patent/US5356368A), Monroe wrote that he coined the term Hemi-Sync for “Hemisphere Synchronization”. You will most often meet it in the Gateway Experience, the home audio course that went viral as the [CIA Gateway tapes](https://shimmr.app/learn/gateway-tapes/). Monroe’s earlier [1975 patent](https://patents.google.com/patent/US3884218A) is often linked to Hemi-Sync, but it describes something different. It covers inducing sleep with familiar, pleasant sounds such as rain on a roof or ocean surf, modulated by the shape of EEG sleep patterns. It does not mention binaural beats at all. ## Hemi-Sync vs binaural beats: what is the difference? The difference is in the layering and the claims, not in the basic sound. A binaural beat is the soft pulse your brain hears when each ear gets a slightly different tone through headphones, for example 200 Hz in one ear and 204 Hz in the other, heard as a 4 Hz beat. Our guide to [what binaural beats are](https://shimmr.app/learn/what-are-binaural-beats/) explains the effect in full. Hemi-Sync recordings, as Monroe’s patent and a [1983 US Army assessment](https://www.cia.gov/readingroom/document/CIA-RDP96-00788R001700210016-5) by Lieutenant Colonel Wayne M. McDonnell describe them, add several things: | | Plain binaural beats | Hemi-Sync | | --- | --- | --- | | Beats | Usually one | Several at once, changing over a session | | Background | Optional | Pink or white noise to mask the tones | | Voice | Usually none | Spoken guidance and affirmations | | Claim | The brain may follow the beat | Both halves of the brain fall into sync | Monroe’s patent calls the core idea a “frequency following response”: the brain is said to follow the rhythm it hears. The 1983 Army report quotes a Monroe Institute trainer who defines Hemi-Sync as a state where the EEG patterns of both hemispheres are “equal in amplitude and frequency”. That is the company’s model, not an established scientific finding. ## What frequencies does Hemi-Sync use? Hemi-Sync uses beats in the ordinary brainwave bands, mostly the slow ones, but the exact mix on each recording is not published. The clearest public example is in the 1994 patent: four carrier tones at 200, 204, 208 and 212 Hz, which produce 4 Hz binaural beats, with pink noise as a masking sound. The same patent also describes beats at beta frequencies for alert states. For context, these are the bands any binaural recording draws on: | Band | Range | Typical state | | --- | --- | --- | | Beta | 12 to 30 Hz | Alert, busy thinking | | Alpha | 8 to 12 Hz | Relaxed, eyes closed | | Theta | 4 to 8 Hz | Drowsy, deeply relaxed | | Delta | 0.5 to 4 Hz | Deep sleep | Lists online that claim a precise “Hemi-Sync frequency chart” are guesses, since the Institute does not publish one. A 4 Hz beat sits at the edge of theta and delta, the zone of drowsiness and the drift into sleep. ## Does Hemi-Sync work? Hemi-Sync may help some people relax, but the evidence is thin and its central claim is unproven. The most cited study is a [1999 double-blind trial](https://doi.org/10.1046/j.1365-2044.1999.00958.x) of 76 patients under general anaesthesia. Those who heard hemispheric-synchronised sounds needed on average 28 micrograms of the painkiller fentanyl, against 124 for classical music and 126 for a blank tape. That is a striking result, but it is one trial in unconscious patients, and it does not show that the two halves of the brain synchronised. On the wider question, a [2023 systematic review](https://doi.org/10.1371/journal.pone.0286023) looked at 14 EEG studies of binaural beats. Five found that brainwaves followed the beat, eight did not, and one was mixed. The authors put this down partly to very different methods. So treat Hemi-Sync, like any binaural audio, as a tool that may help you settle, not a proven switch for your brain. Our article on [whether binaural beats work](https://shimmr.app/learn/do-binaural-beats-work/) covers the research in more depth. ## Is Hemi-Sync dangerous? Hemi-Sync is low risk for most people when you listen at a low volume. There is no good evidence that binaural beats damage the brain or the mind. The real risks are ordinary ones: slow beats make you drowsy, so never listen while driving or doing anything that needs your full attention. Keep the volume low, since the beat works at a quiet level and loud sound over hours can harm hearing. If you have epilepsy or a seizure disorder, talk to your doctor before using rhythmic sound. If long sessions leave you feeling unsettled or disconnected, stop and take a break. ## How can you try binaural beats yourself? You can try the sound that sits under Hemi-Sync with any good binaural session and a pair of headphones. Lie down, keep the volume low and give it 15 to 30 minutes. Shimmr is not Hemi-Sync and has no link to the Monroe Institute, but it does play binaural sessions from Delta to Gamma, and you can layer pink or brown noise, rain or your own music under them in the mixer. The Tense → At Ease Shift glides from Beta to Theta over 15 minutes. In Sound Canvas you can drag a tone and hear its beat change while it plays. - [Hemi-Sync alternative Under Hemi-Sync are binaural beats. Here, you can shape them.](https://shimmr.app/hemi-sync-alternative/) In the app Sound Canvas Drag binaural tones into a space and hear each beat change live as you move it. ## Common questions **What is Hemi-Sync?** Hemi-Sync is an audio method developed by Robert Monroe and used in Monroe Institute recordings such as the Gateway Experience. It layers binaural beats with masking noise and, in many recordings, spoken guidance. **Is Hemi-Sync the same as binaural beats?** Not quite. Hemi-Sync is built on binaural beats, but it blends several beats with pink noise and voice, and adds the claim that it synchronises the two halves of the brain, which research has not established. **What frequencies does Hemi-Sync use?** The exact mixes on Monroe recordings are not published track by track. A 1994 Monroe patent shows one example: tones at 200, 204, 208 and 212 Hz that produce 4 Hz binaural beats, in the theta to delta range. **Does Hemi-Sync work?** Some people find it deeply relaxing, and one 1999 trial found lower painkiller use under anaesthesia. But a 2023 review of 14 studies found that binaural beats change brainwaves in some studies and not in others. **Is Hemi-Sync dangerous?** There is no good evidence that it is harmful at a low volume. Because it can make you drowsy, do not listen while driving, and if you have epilepsy ask your doctor before using rhythmic sound. Keep reading - [Meditation The Gateway tapes: what they are, what the CIA report says and the binaural beats inside](https://shimmr.app/learn/gateway-tapes/) - [Science What are binaural beats and how do they work?](https://shimmr.app/learn/what-are-binaural-beats/) - [Science Do binaural beats work? What the research actually shows](https://shimmr.app/learn/do-binaural-beats-work/) This article is for general information and is not medical advice. Binaural beats are not a treatment for insomnia or any other condition.