Why we measure your voice instead of your brainwaves

In our practice office in Sofia, we record two minutes of EEG before and after every audio-visual entrainment session. We have recorded more than 1000 sessions with 170 people. At home, almost nobody owns an EEG headset. So the 6th Mind app uses something everyone already carries. You speak for about a minute and the app gives you a daily Wellbeing score from 0 to 100, free with an account. Here is the reasoning behind that, and what the score is and isn’t.

What we measure in the practice office

Before every session, we use a Muse band to record two minutes of EEG. We measure alpha peak frequency, alpha and beta power, entropy and alpha asymmetry. We record for two minutes again after the session. People also answer questionnaires when a programme begins and when it ends.

We use those numbers to calculate two values. The Session Improvement Index is how the data changes during one visit. The Baseline Index is how resting activity changes over ten to fifteen sessions. In those records about 80% of the programmes that reached ten or more sessions (n≈70) improved on the Baseline Index. Those are the completers, because not every programme runs that long.

That body of measurements built the AI data model for the 6th Mind sessions. The frequency sequences, the thirty-second ramps and the carrier re-tuning all come from comparing the EEG before and after sessions. We explain more in who we are and how we measure.

Why EEG doesn’t move into your living room

The first reason is that almost no one has an EEG headset, and we are not going to ask anyone to buy hardware to use a free app.

The second reason is that consumer headbands have one to four sensors, while clinical equipment has 19 to 256. Papers that test both kinds state that consumer devices record a genuine signal, but a coarse one. Those devices also change their output if the band doesn’t sit tightly on the head, if a person moves or if a person clenches their jaw. A small sensor array reads all of that as brain activity. In our office a trained person places the band the same way every time. At home a reading taken wrong is worse than no reading at all. There is more on that hardware in our look at consumer EEG wearables.

Why the voice

The way a person speaks changes based on how they feel. That shows in the tone, the pace and the length of the pauses. Scientists have studied speech and mental states for more than ten years. A systematic review from 2020 covers 127 studies on automated assessment from speech, and a 2015 review in Speech Communication maps the acoustic markers. Many of those papers are about screening for depression, and the field is still maturing; the authors of the reviews say so themselves.

So we are deliberate about what we take from that work. The Wellbeing score is an indicator of how you are each day; it does not screen for or detect any condition. We use voice because it is easy to record: the microphone is already in your pocket.

How Mental wellbeing works in the app

Before you start the first session of the day, you speak for about a minute about an everyday topic the app suggests, like your favourite season. An AI model on our own server listens to how you speak, not to what you say, and returns a Wellbeing score from 0 to 100. Higher is better. You can run up to four checks in 24 hours.

We trained the model on thousands of recordings of people talking about everyday topics, who also filled in standard mental health questionnaires. Mental wellbeing is free with a 6th Mind account, isn’t part of Premium and works in English only for now.

Why one score means little and the trend means a lot

A single check can land roughly 7 to 8 points higher or lower depending on how much you slept, the time of day and what you were doing ten minutes earlier. No conclusion should rest on one number.

The “My activity” section keeps your score, a 30-day chart and, after seven daily checks, an indication of whether the score is changing. To make that trend readable, record at about the same time each day, in a quiet place.

	Practice office	6th Mind app
What’s measured	Two minutes of EEG before and after each session	About a minute of your voice, once a day
What it outputs	Session Improvement Index, Baseline Index	Wellbeing score from 0 to 100, trend after 7 checks
Questionnaires	When the programme starts and when it ends	Day 1 and after day 15
Cost	Paid sessions	Free with an account

How the score fits personalisation

Three inputs tell the app what works for you, and your voice recording is one of them. The questionnaire on day 1 builds your 15-day programme. Then, once you have enough daily checks, 6th Mind builds your routine around the sessions and frequency profiles that work best for you. The questionnaire after day 15 shows what changed and shapes the next programme.

Each session itself is open-loop: nothing changes while it plays. The loop closes between days, which is the distinction we drew in open-loop vs closed-loop stimulation.

Privacy and what the score isn’t

The model runs on our own server. Your recording isn’t turned into text or shared, and it’s deleted as soon as it’s analysed. Only the score is kept. The app asks for your explicit consent before your first check, and you can delete checks from My activity.

The Wellbeing score helps you follow how you’re doing. It is not a diagnosis or a medical test. To try it, the 6th Mind app is free on iOS and Android, and the Wellbeing score page walks through a check step by step.

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Sources

• “Automated assessment of psychiatric disorders using speech: A systematic review” - Laryngoscope Investigative Otolaryngology, 2020
• “A review of depression and suicide risk assessment using speech analysis” - Speech Communication, 2015
• “Comparison of EEG Signal Spectral Characteristics Obtained with Consumer- and Research-Grade Devices” - Sensors, 2024