Guides

Audio formats, quality and file size on a Mac

Updated 2026-09-03.

Audio format decisions on a Mac come down to three numbers. Bit depth sets the noise floor (24-bit is 50 percent larger than 16-bit). Sample rate sets the frequency ceiling (48 kHz is 9 percent larger than 44.1 kHz). Codec sets the size: 24-bit 48 kHz PCM is 16.5 MB per minute, MP3 320 kbps is 2.4 MB, measured on 45 real recordings. Distortion and dropouts happen at the input, before any of those choices, and cannot be repaired afterwards.

Guides in this topic

1. How big is an audio recording per minute on a Mac?Measured from 45 real Mac recordings: 24-bit 48 kHz WAV is 16.5 MB per minute, 16-bit 48 kHz is 11.0 MB, MP3 320 kbps is 2.4 MB. Hours per GB inside.
2. WAV vs AIFF vs MP3: which format should you keep on a Mac?WAV and AIFF hold identical PCM audio (16.5 MB per minute at 24-bit 48 kHz); MP3 320 is 2.4 MB per minute and lossy. Keep PCM, share MP3.
3. 16-bit vs 24-bit audio recording: which should you choose?24-bit gives about 146 dB theoretical dynamic range against 98 dB for 16-bit and costs 50 percent more disk (16.5 vs 11.0 MB per minute). Choose by source.
4. 44.1 kHz vs 48 kHz: which sample rate should you record at?48 kHz is the video and macOS system-audio rate, 44.1 kHz the CD and music rate. Files differ by 9 percent (16.5 vs 15.1 MB per minute). Match your source.
5. How to convert AIFF or WAV to MP3 on a MacmacOS has no MP3 encoder in afconvert. Use the Music app (File > Convert > Create MP3 Version), ffmpeg with libmp3lame, or LAME. Commands inside.
6. How to convert a Mac recording to M4A or AACOne built-in command: afconvert -f m4af -d aac -b 256000 in.wav out.m4a. AAC beats MP3 at equal bitrate; 256 kbps is about 1.9 MB per minute.
7. Why does my recording sound distorted or clipped on a Mac?Distortion in a Mac recording is almost always clipping: the input hit 0 dBFS. Hard clipping cannot be repaired afterwards. Lower the gain, record 24-bit.
8. Why is there a gap or dropout in my Mac recording?Gaps in Mac recordings come from USB stalls, Bluetooth switches, sleep, or sample-rate changes. How a watchdog restarts capture after 5 s and what is lost.
9. What sample rate does Mac system audio use?System audio via ScreenCaptureKit arrives at 48 kHz on the author's Mac (macOS 26.4.1). Change a device's rate in Audio MIDI Setup's Format pop-up.

Which format should I record in on a Mac?

Record PCM (WAV or AIFF) at 24-bit whenever a human sets the gain: DJ sets, vinyl, instruments, interviews on a microphone. The extra bits give about 146 dB of theoretical range against 98 dB for 16-bit, so you can leave headroom without hiss, and the cost is 16.5 instead of 11.0 MB per minute at 48 kHz. The reasoning and the size table are in 16-bit vs 24-bit.

Record 16-bit WAV or MP3 320 kbps when the source is already lossy or level-controlled: a YouTube video, a Spotify stream, a Zoom call, a lecture. A 90-minute lecture is 990 MB at 16-bit 48 kHz and 216 MB as MP3. WAV and AIFF hold identical samples and differ only in the wrapper; MP3 discards detail for a 6.9 times smaller file. The keep-or-share decision is in WAV vs AIFF vs MP3, and every combination's size per minute, hours per GB and per-duration figures are in how big is an audio recording per minute. For the sample rate, match the source: system audio arrives at 48 kHz on the author's Mac, measured in what sample rate does Mac system audio use, and the general choice is in 44.1 kHz vs 48 kHz.

How do I convert a recording to a smaller format on a Mac?

Apple ships one converter, afconvert, in every macOS. It converts between WAV and AIFF at any bit depth, resamples, and writes AAC or Apple Lossless into an .m4a: afconvert -f m4af -d aac -b 256000 in.wav out.m4a gives a file of about 1.9 MB per minute against 16.5 MB for the 24-bit 48 kHz master (size table), and AAC generally beats MP3 at the same bitrate. The command, its bitrates and the ALAC option are in how to convert a Mac recording to M4A or AAC.

What afconvert cannot do is write MP3. Tested on macOS 26.4.1, the attempt fails with ExtAudioFileSetProperty ('cfmt') failed ('fmt?'), because macOS includes no MP3 encoder. The free routes are the Music app (Music > Settings > Files > Import Settings, then File > Convert > Create MP3 Version), or ffmpeg -i in.wav -c:a libmp3lame -b:a 320k out.mp3 and lame -b 320 in.wav out.mp3 after a Homebrew install. Bitrate arithmetic (320 kbps is 2.4 MB per minute, 128 kbps is 0.96) and the VBR settings are in how to convert AIFF or WAV to MP3. Keep the PCM master at the rate the capture delivered (what sample rate does Mac system audio use); compressed-to-compressed conversion loses quality each time. Pulling audio out of a screen recording or video uses the same tools and is covered in how to extract audio from a video file.

Why does my Mac recording sound distorted or have gaps?

Both problems happen at the input, before the file format matters, and neither can be repaired afterwards. Distortion is clipping: the signal reached 0 dBFS, the top of the digital scale, in the interface's preamp or converter, and the peaks were flattened. Hard-clipped audio cannot be restored because the information in the peaks is gone; de-clippers only estimate. The fix is upstream: set the gain on the loudest passage, use a line input for a mixer output, and record 24-bit so a conservative level costs nothing (16-bit vs 24-bit). The full diagnosis table is in why does my recording sound distorted or clipped.

A gap is a stretch where the device delivered no audio: a USB interface on a hub stalled, AirPods switched profiles, another app changed the sample rate (44.1 kHz vs 48 kHz), or the Mac slept. Most recorders keep a dead stream open; AirCheck's watchdog restarts capture into the same file after 5 seconds without audio and keeps retrying, but the seconds of the stall are still silent. Prevention is a direct USB port, the rate set once in Audio MIDI Setup, caffeinate -i, and free disk (0.97 GB per hour at 24-bit 48 kHz). Causes and fixes are in why is there a gap or dropout in my Mac recording; clicks without gaps are buffer underruns, treated on the same page.

Format decision table for Mac recordings (sizes measured on 45 real files)

PCM and MP3 rows are measured; the AAC row is bitrate / 8 x 60. Distortion and dropouts are independent of the row you pick.

Other topics

• Screen recording with audio
• Recording internal and system audio
• Recording calls and meetings
• Recording streams, music and video sound
• Virtual audio drivers and Audio MIDI Setup
• Recording with QuickTime, OBS, Audacity and GarageBand
• Recording DJ sets, vinyl and instruments
• Recording lectures, podcasts and interviews
• Fixing Mac audio recording problems
• Choosing a Mac audio recorder