Bluetooth and AirPods: what actually reaches your ears

The path from file to ear

More happens with wireless headphones than you see from the outside. Simplified, your music passes through these stages:

• Decoding: the app reads the file, whether FLAC, AAC or MP3, and turns it into uncompressed PCM data.
• Mixing: the system applies volume, equalizer and other sounds such as notifications.
• Re-encoding: for the radio link the result is compressed again with a Bluetooth codec.
• Transmission: the data travels in the 2.4 GHz band, which it shares with Wi-Fi, other Bluetooth devices and microwave ovens.
• In the headphones: a dedicated chip decodes, applies sound correction, noise cancellation and possibly spatial audio, and a built-in converter and amplifier drive the speaker.

Two consequences are often overlooked. First, with Bluetooth the codec determines quality on the radio link, not the file format. Second, the converter in your phone no longer matters, because the conversion to analogue happens in the headphones. Buying a phone for its audio chip and then listening wirelessly gains you nothing.

Bluetooth codecs at a glance

For comparison: uncompressed CD quality needs 1,411 kbps. Even the fastest lossy Bluetooth codecs sit below that, and the rate actually achieved fluctuates with the radio link.

SBC

The baseline codec every Bluetooth audio device must support. With the usual settings SBC reaches about 330 kbps. Its reputation is worse than it needs to be: implemented well, SBC sounds decent, but many cheap devices use lower settings. When a better connection fails, every device falls back here.

AAC

Apple uses AAC for all its own headphones. iPhone and iPad also talk to other brands' headphones only via AAC or SBC; aptX and LDAC aren't supported. Independent measurements usually put the iPhone at around 256 kbps. AAC is an efficient codec and at that bitrate transparent in blind tests for almost all listeners, meaning indistinguishable from the original. On Android, AAC is a gamble: depending on manufacturer and device, the encoder varies a lot in quality.

The aptX family

Qualcomm's codecs are widespread on Android. Classic aptX delivers 352 to 384 kbps with low latency, aptX HD 576 kbps at 24-bit. aptX Adaptive continuously adjusts its bitrate to the connection. aptX Lossless extends it and can transmit CD quality truly losslessly, but only if both phone and headphones support Snapdragon Sound and the radio link is stable. Under interference it falls back to lossy levels, reportedly down to 140 kbps.

LDAC

Sony's codec has been part of Android since version 8. With up to 990 kbps and up to 24-bit/96 kHz it's on paper the most capable lossy codec. In practice LDAC often runs at 330 or 660 kbps, because 990 kbps needs a very stable connection, such as the phone in your hand rather than your back pocket. A hi-res logo on the box doesn't mean hi-res arrives.

LE Audio and LC3

The newer Bluetooth LE Audio standard brings the LC3 codec, which sounds better than SBC at the same bitrate and uses less power. It also enables Auracast, broadcasting to many receivers at once. For music on the iPhone, LE Audio plays no role so far, as far as is publicly known. Apple continues to use AAC for AirPods.

iPhone and AirPods in detail

Apple states plainly in its support article on lossless audio that Bluetooth connections aren't lossless. AirPods and most Beats headphones use Apple's AAC codec. In practice:

• On iPhone, iPad and Mac all AirPods play via AAC. That includes AirPods Pro 3 and AirPods 4.
• With Apple Vision Pro, AirPods 4, AirPods Pro 3 and AirPods Pro 2 with the USB-C case play lossless. For AirPods Pro 2, Apple quotes 20-bit/48 kHz over its own wireless link in the 5 GHz band. That isn't available on the iPhone.
• AirPods Max with USB-C have played lossless 24-bit/48 kHz since an update in spring 2025, when connected with the USB-C cable. Over the analogue 3.5 mm cable it isn't lossless, because the signal is digitised again inside the headphones.

Then there's the processing in the headphones: Adaptive EQ continuously adjusts the sound to the fit, and spatial audio with head tracking renders a virtual room. Both change the signal far more than any codec. That's not a flaw; it's what the headphones are tuned for. But it shows that "bit-perfect" isn't a meaningful yardstick for wireless headphones.

Double compression

If the file on your iPhone is AAC, it's still decoded and re-encoded for the AirPods, because the system has to apply volume and mix in other sounds. The signal has then been lossily encoded twice. At 256 kbps in both stages that's practically inaudible, going by what blind tests show. With heavily compressed files, such as 128 kbps MP3, artefacts are more likely to add up. A good reason not to skimp on the bitrate of your phone copy.

Android: more choice, more pitfalls

On Android, phone and headphones negotiate the best common codec when they connect. The developer options show, and partly let you choose, which codec is active. A few things worth knowing:

• Both ends count. An LDAC phone with aptX headphones ends up on SBC or AAC if there's no common denominator.
• Higher bitrate has a cost. LDAC at 990 kbps uses more battery, shortens range and tends to drop out in crowded places like train stations. Many headphone apps therefore let you choose between sound quality and a stable connection.
• Hi-res over Bluetooth stays lossy. Squeezing a 24-bit/96 kHz signal into 990 kbps takes far more compression than a CD signal.

Can you hear the difference?

For AAC at 256 kbps, aptX HD or LDAC at 660 to 990 kbps, the same applies as for well-compressed files: under controlled conditions, level-matched and without knowing what's playing, most people can't tell them from the original. The studies are covered in detail in music file formats explained.

Other things are clearly audible, though:

• Fit and seal: in-ear headphones only sound good when they seal the ear canal. An ear tip in the wrong size costs bass above all, more than any change of codec. AirPods Pro have an Ear Tip Fit Test in their settings for this.
• Tuning: two headphones with the same codec can sound completely different. The manufacturer's tuning shapes the sound most.
• Noise cancellation: on a train or plane, good noise cancellation lets you hear more detail than the best codec without it, because you can listen at lower volume and the noise doesn't mask anything.
• Volume: louder sounds better at first. Equal levels are the precondition for any fair comparison.
• Radio interference: dropouts and brief switches to lower levels are more noticeable than the difference between two codecs.

If you really want lossless

Then there's no way around a cable. The options on the iPhone:

• USB-C headphones or Apple's USB-C to 3.5 mm adapter. Without an additional converter the iPhone outputs up to 48 kHz according to Apple, and the little adapter measures well in independent tests despite its price. Older iPhones have the same with Lightning.
• External converter (DAC): for sample rates above 48 kHz the iPhone needs an external converter, says Apple. Small USB-C dongles with a headphone output come in every price range. They draw power from the iPhone; larger models with their own battery spare it.
• AirPods Max with USB-C on the USB-C cable, lossless at 24-bit/48 kHz.

On the Mac, Apple says the 14- and 16-inch MacBook Pro have a headphone jack that plays natively up to 96 kHz. Other Macs need an external converter for higher rates.

Whether it's worth it is an honest trade-off. With good wired headphones in a quiet room you get the full quality of your files. On the go, convenience and noise cancellation win for most people.

What this means for your collection

• If you listen almost only wirelessly, a 256 kbps AAC copy on the phone is enough. Over AirPods it sounds practically like FLAC and takes about a third of the space.
• Keep the archive lossless anyway. Any smaller copy can be made from FLAC at any time, and on a hi-fi system, a Mac or with a cable you hear the full quality. How to keep archive and copy apart is in organising a music library.
• Hi-res isn't worth it for wireless headphones. Over AirPods on an iPhone, a hi-res signal never arrives.

Luma plays both lossless and compressed files on iPhone, iPad and Mac. The equalizer and volume normalisation act before the Bluetooth transmission. If you listen wired and want the signal output unchanged, turn both off, along with cross-fade. More in the help center under Equalizer, volume and cross-fade.

Frequently asked questions

Do AirPods play lossless audio?

Not on iPhone, iPad or Mac. There all AirPods use the Bluetooth codec AAC, and Apple itself says Bluetooth connections aren't lossless. AirPods 4, AirPods Pro 3 and AirPods Pro 2 with the USB-C case play lossless only with Apple Vision Pro, and AirPods Max with USB-C on the USB-C cable.

Is FLAC on my iPhone worth it if I use AirPods?

Hardly. The iPhone re-encodes every file to AAC for the AirPods. A 256 kbps AAC copy sounds practically the same over AirPods and takes about a third of the space. For your archive and for wired listening, FLAC is still the right choice.

Does the iPhone support aptX or LDAC?

No. iPhone and iPad send audio to Bluetooth headphones only with AAC or SBC. Headphones with aptX or LDAC work with an iPhone, but they run on AAC there.

Which Bluetooth codec sounds best?

On paper aptX Lossless, which can transmit CD quality losslessly when phone and headphones support Snapdragon Sound. In blind tests, though, AAC at 256 kbps, aptX HD and LDAC are already indistinguishable from the original for most people. Fit and tuning of the headphones matter more.

Does a newer Bluetooth version improve sound quality?

Not directly. Newer versions mainly improve range, stability and power consumption. The quality that arrives is set by the codec phone and headphones agree on.

Sources

• Apple Support: About lossless audio in Apple Music (Bluetooth, AirPods, external converters). support.apple.com/en-us/118295
• AirPods Pro 2 with USB-C: 20-bit/48 kHz lossless audio with Vision Pro (UploadVR, September 2023). uploadvr.com
• Lossless audio for AirPods Max over USB-C (What Hi-Fi?, March 2025). whathifi.com
• aptX Lossless: how it works and what you need (What Hi-Fi?). whathifi.com
• Sony: LDAC, transmission rates and sample rates. sony.net/Products/LDAC
• SBC, the mandatory Bluetooth codec, and typical bitrates (Wikipedia). en.wikipedia.org/wiki/SBC_(codec)

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