Guides / Audio formats, quality and file size
Why is there a gap or dropout in my Mac recording?
Tested on macOS 26.4.1 (Tahoe), Apple M3 Max, 3 Sept 2026. Updated 2026-09-03.
A gap or dropout means the audio device stopped delivering buffers for a while: a USB interface lost power or bandwidth, a Bluetooth device switched profiles, another app changed the sample rate, or the Mac slept. Core Audio does not fill the hole. AirCheck's watchdog checks every 2 seconds and, after 5 seconds without audio, restarts capture into the same file; the missing seconds are still gone.
What causes a gap or dropout in a recording?
Core Audio delivers audio to a recorder as a stream of buffers. A gap is a stretch where no buffers arrived, or arrived too late to be written. The usual triggers, roughly in order of how often they show up in support mail:
- USB interface stalls. A bus-powered interface on a hub, a long or damaged cable, or another hungry USB device sharing the bus. The device drops off and comes back with a new Core Audio device ID.
- Bluetooth changes. AirPods connecting or disconnecting, or switching from the music profile to the headset profile when an app opens the mic, changes the active device mid-take.
- Sample rate changes. Another app (a DAW, DJ software, a browser call) sets the device to a different rate; the stream restarts. See 44.1 kHz vs 48 kHz.
- Sleep. A closed lid or an idle timeout stops everything; covered in Mac recording stops when the display sleeps.
- Disk full. At 16.5 MB per minute for 24-bit 48 kHz a 2-hour take needs 2 GB; a nearly full drive ends the file early.
Distortion without gaps is a different problem, see why does my recording sound distorted.
How does a recorder recover when the input stalls?
Most recorders do not. QuickTime Player and Audacity keep a dead stream open and you find out at the end. AirCheck's approach, documented here because it is the one first-party design detail on this page:
- A watchdog timer runs every 2 seconds while recording.
- If no audio buffer has arrived for 5 seconds, the capture session is torn down.
- Capture is restarted into the same file, so the take stays in one piece rather than splitting into parts.
- If the device is still missing, it retries forever until it comes back or you press stop. The interface shows "Audio input stalled, reconnecting".
- The device is re-resolved by name, not by ID, because Core Audio assigns a new device ID every time a USB or Bluetooth device reconnects.
What this does not do: it cannot recover audio from the stall itself. Five seconds of detection plus the reconnect time is silence in the file, and no software can invent the music that played while the interface was unplugged. Recovery makes the take continue; prevention is what keeps it complete.
How do I prevent dropouts in a long recording?
- Plug the audio interface straight into the Mac, not through a hub, and use the cable it shipped with. Bus-powered interfaces on a hub are the top cause of USB stalls.
- Set the sample rate in Audio MIDI Setup before the take and leave it. Close DJ or DAW software that might change it, or make sure it uses the same rate.
- Keep the Mac awake: System Settings > Battery (or Energy) > prevent sleep on power adapter, or run
caffeinate -iin Terminal for the duration. - For system audio, do not connect or disconnect AirPods or other Bluetooth devices during the take. Pick the output device first, then record.
- Check free disk space against the plan: hours x 0.97 GB at 24-bit 48 kHz, or x 0.14 GB at MP3 320 kbps, from how big is an audio recording per minute.
- For a live set, run a second recorder in parallel: the DJ software's own recorder, or a hardware recorder on the booth output.
A stable setup on the author's Mac has produced a 7,550-second (2 h 5 min) take without a single stall, so the hardware is capable; the causes above are almost always environmental.
What about clicks and stutter rather than a gap?
Short clicks, crackle or a stuttering repeat of a fraction of a second are buffer underruns: the recorder was not given CPU time to fetch a buffer before the next one arrived. Unlike a dropout, the device never left. Typical causes are an interface buffer size set very small in a DAW that also owns the device, a Bluetooth headset profile active at the same time as a USB interface, heavy CPU load from video export or a browser with many tabs, or an aggregate device combining two clocks without drift correction. The remedies are the same order: direct USB, one app owning the device, a larger buffer in the DAW if one is running, and no clock-mismatched aggregate device for a plain stereo take. If the clicks are periodic and the recording also runs slightly long or short, two devices are drifting against each other, and the fix is the drift-correction checkbox in Audio MIDI Setup's aggregate device.
Dropout causes, what is lost, and whether capture resumes on its own
| Cause | What you hear | Audio lost | Auto-resumes in AirCheck | Prevention |
|---|---|---|---|---|
| USB interface stall or unplug | silence, then audio returns | stall length plus up to 5 s detection | yes, same file | direct port, original cable, no hub |
| Bluetooth device connects or switches profile | silence or a change in tone | seconds around the switch | yes, same file | choose the output before the take, do not touch it |
| Sample rate changed by another app | silence or pitch shift | seconds around the change | yes, same file | set the rate in Audio MIDI Setup first, close conflicting apps |
| Mac sleeps | recording ends or silent tail | everything after sleep | no, take stops | disable sleep, caffeinate -i |
| Disk full | file ends early | everything after the limit | no | plan 0.97 GB per hour at 24-bit 48 kHz |
| Buffer underrun | clicks, stutter | milliseconds | not applicable (no stall) | lower CPU load, larger DAW buffer, one owner per device |
Detection and reconnect behaviour are AirCheck's documented design; other recorders may stop silently.
Where AirCheck fits
AirCheck ($39, macOS 14 or newer) was built around long DJ takes through a Scarlett 8i6, where an unplugged cable at minute 90 must not cost the first 89 minutes. Its watchdog restarts capture into the same file after 5 seconds without audio and keeps retrying, handles hot-plug by re-resolving the device by name, and shows the stall in the UI. Files land as one continuous take of the format you chose, up to the 2 h 5 min longest real take so far.
When you do not need it: If your recordings never stall (built-in mic, short takes), QuickTime Player is free and fine. AirCheck cannot restore audio from the stall itself and has no silence detection or editing; for surgical repair of clicks you need a DAW or iZotope RX.
AirCheck records what your Mac plays, or any input, to one file. $39 once.
macOS 14 or newer. One-off payment. Fourteen-day refund, no questions asked.
Questions people ask
Why does my audio recording keep cutting out on Mac?
Most often a USB interface on a hub or a bad cable, a Bluetooth device switching, another app changing the sample rate, or the Mac going to sleep. Plug the interface directly into the Mac, set the rate first, keep the Mac awake with caffeinate -i, and leave Bluetooth alone during the take.
Can the missing audio in a dropout be recovered?
No. During a stall no samples reach the Mac, so there is nothing to recover. A recorder can only resume; AirCheck does so into the same file after 5 seconds without input. A parallel backup recorder is the only real insurance for a live set.
Why does my recording stop when I close the MacBook lid?
Closing the lid sleeps the Mac unless it is on power with an external display or sleep is disabled. Sleep stops Core Audio, so the take ends. Keep the lid open, or run caffeinate -i in Terminal for the session.
Does recording as MP3 reduce dropouts?
No. Dropouts happen at the input device, before any encoding. The only format-related cause is a full disk, and there MP3 helps: 0.14 GB per hour against 0.97 GB at 24-bit 48 kHz.
Sources
- AirCheck: dropout watchdog design and measured sizes (first-party)
- Apple: Set up audio devices in Audio MIDI Setup (Format pop-up sets sample rate)
Related guides
- Why does my recording sound distorted or clipped on a Mac?
- 44.1 kHz vs 48 kHz: which sample rate should you record at?
- Why does my Mac recording stop when the display sleeps?
- Why is my USB audio interface not showing up on my Mac?
- How big is an audio recording per minute on a Mac?
- WAV vs AIFF vs MP3: which format should you keep on a Mac?
- Audio formats, quality and file size: all guides
- Every guide, by topic