How your breathing sounds become stage estimates, and how to read them.
Snore Timeline estimates which sleep stage you were in at each point of the night. Awake, Light Sleep, Deep Sleep, or REM, plus a fifth label called Silence for stretches where it couldn't hear anything at all. The estimates come from your breathing sounds alone, picked up by the same microphone that does the snore detection. This page goes through the signals behind each stage, how to read the hypnogram in your nightly summary, and what the estimates can and can't tell you.
Your breathing changes as you move through the stages of sleep, and you can hear the difference. The app looks at how regular your breathing is and how much it varies, using the same recording it already uses for snore detection and breathing disruption detection. There's nothing extra to set up.
About 15 minutes into a recording, the algorithm works out your personal breathing baseline, meaning your typical rate and regularity. From there it measures the rest of the night against your own baseline instead of a population average, and applies thresholds from published research to sort each period into a stage.
Breathing regularity carries most of the weight, but the algorithm also looks at:
The result shows up as a hypnogram in your nightly summary.
Each stage leaves its own fingerprint in your breathing:
Deep Sleep sits at one end of the regularity scale and REM at the other, so the app wants to see consistently low variance before it calls a period Deep Sleep, and it drops out of Deep Sleep as soon as variance climbs. The sound classification running alongside adds the snore and movement context.
Staging from audio has one built-in limit. It can only classify what it can hear. When your breathing is too soft for the microphone to sort into a stage, and nothing suggests you're awake, the app marks that stretch as Silence instead of guessing. This happens a lot for quiet breathers, or when a fan or air conditioner covers the sound.
Silence counts as restful sleep. It goes toward your total sleep time and earns credit toward the restorative part of your sleep score, so a quiet night still reads as a good one. Making up a stage from no evidence would make the data less trustworthy, so the app labels the uncertainty and leaves it at that.
Two breathing measurements feed the stage model, and both show up in your results:
Both are estimates from audio, for your own insight. If your respiratory rate is well outside the normal range, bring it to a doctor instead of trying to diagnose yourself.
Yes, when it's there. If a wearable like Apple Watch reports sleep stages for the night, Snore Timeline uses the watch's Deep and REM percentages for your sleep score instead of its own audio estimates. A wearable measures those stages better than audio can, so the app defers to it. Without a wearable, it falls back to the breathing and movement estimates. The Apple Watch page covers what the watch adds.
The hypnogram in your nightly summary charts how you moved through the stages over the night. Each colored band is 5 minutes in a given stage:
Read it left to right and you can count how many full sleep cycles you went through, see when you got the most Deep Sleep, and spot where REM landed. Tap any block and a pill shows that stage's full time range, like "Light · 3:50am – 4:15am", and the timeline moves to that moment so you can check whether your snoring episodes line up with a particular stage. Scrub the timeline afterward and the hypnogram's selection line follows.
On nights where a wearable synced sleep data but you didn't record audio, the timeline strip draws a stage ribbon in the same colors, and the status bar reads out the stage and your vitals under the center line, like "Light · 57 bpm · 13 br/min · SpO2 96%". Recorded nights keep the plain waveform.
The nightly summary also shows what percentage of the night you spent in each stage. A typical night might look something like:
Those percentages shift with age, health, stress, and plenty else, so compare your own nights against each other and don't worry about matching a textbook. For scoring, the app treats Deep Sleep of roughly 13 to 23 percent as a healthy target, with 20 percent or more earning credit toward your score, and REM of about 20 to 25 percent. Landing in those ranges can add points to your sleep score. They're general guidelines and nothing more.
The classification is based on published research into how breathing regularity relates to sleep stages. Studies that stage sleep from a single physiological signal, like breathing or heart-rate variability, reach roughly 70% agreement with polysomnography, which is the clinical sleep study standard. So the estimates give you a fair picture of your general sleep architecture, and a better one of your trends over time.
A few things push accuracy up or down. Longer recordings help, because several hours of sleep gives the app more complete cycles to look at. A noisy room, a bed partner, pets, or sleeping far from the microphone all make your breathing harder to detect, and the estimates get worse with it.
These are estimates from audio analysis. They aren't clinical measurements. Clinical sleep staging uses brain waves, eye movement, and muscle activity, none of which audio can capture. Snore Timeline hasn't been validated against polysomnography and can't diagnose sleep apnea or any sleep disorder. Treat the stage breakdown as a general guide, and talk to a healthcare professional if you have concerns about your sleep.
Stage estimation needs audible breathing through the recording. If a night shows no stages, it's usually one of these:
Use the same phone placement every night, quiet the room where you can, and record full nights. Recordings of 6 hours or more give the algorithm the most complete cycles to work with, and keeping the placement the same keeps your nights comparable.
If the whole timeline came up empty, and it's more than the stages missing, see Troubleshooting.
The stage classification draws on these papers:
