Learn
Bluetooth codecs and latency: SBC, AAC, aptX, LDAC, LC3
Bluetooth doesn't have enough bandwidth to carry uncompressed audio. So it needs a codec, a process that slims the signal down before sending it. Manufacturers turn codecs into a selling point; the reality is more nuanced, and the codec isn't always where quality is won or lost.
Why audio has to be compressed
CD-quality music amounts to 1,411 kilobits per second. A classic Bluetooth audio link offers a few hundred kilobits in good conditions, and far fewer in a subway car saturated with radio signals. A codec (coder-decoder) lowers the bitrate by discarding the information the ear perceives least, following the principles of psychoacoustics: a quiet sound masked by a louder one nearby, for example, is not transmitted.
The phone encodes; the headphones decode. So both devices have to speak the same codec. When they connect, they choose the best one they have in common; failing that, they fall back to SBC, which every Bluetooth audio device is required to support.
The codecs in one table
| Codec | Maximum bitrate | Compatibility | Key point |
|---|---|---|---|
| SBC | ≈ 328 kbps | Universal | Decent at full bitrate, often throttled |
| AAC | ≈ 256 kbps | Apple, most Android devices | Excellent on iPhone, uneven on Android |
| aptX | 352 kbps | Android, Windows | In practice, on par with a good SBC |
| aptX HD | 576 kbps | Android | Up to 24-bit/48 kHz |
| aptX Adaptive | 279 – 420 kbps, variable | Recent Android devices (Qualcomm chips) | Adapts to radio conditions, low latency |
| aptX Lossless | ≈ 1 Mbps | A few recent Android devices | Lossless CD quality if the signal allows |
| LDAC | 330 / 660 / 990 kbps | Android | Up to 24-bit/96 kHz, sensitive to interference |
| LC3 | Variable | LE Audio devices | Better than SBC at the same bitrate, energy-efficient |
Can you hear the difference?
Less than the spec sheets suggest. Blind listening tests have shown it for a long time: well-encoded AAC at 256 kbps is indistinguishable from the original for the vast majority of listeners, on the vast majority of music. SBC at full bitrate isn't far behind.
Audible differences mostly arise in three situations:
- A collapsing bitrate. When the radio signal is poor, the codec lowers its bitrate. LDAC that has dropped to 330 kbps does no better than AAC.
- A mediocre encoder. The quality of AAC depends heavily on its implementation: remarkable from Apple, variable from brand to brand on Android.
- Double compression. Streamed music is already compressed; the Bluetooth codec compresses it again. Two successive rounds of compression add up, which argues for a good-quality source.
The real hierarchy is clear: the headphones (their drivers, their tuning, their fit) matter vastly more than the codec. Excellent headphones over AAC beat average headphones over LDAC.
Which codec with which phone
- iPhone, iPad: AAC, and nothing better. aptX and LDAC are useless in this ecosystem.
- Android with a Qualcomm chip: aptX and its variants, plus LDAC on most models.
- Other Android devices: SBC, AAC and usually LDAC, built into the system since Android 8.
- Windows: SBC, AAC and aptX, depending on the version and the adapter.
On Android, the developer options show the codec actually in use: it's the only way to check that the promised "high-resolution" audio is really active.
Latency, where the codec really matters
Encoding, transmitting, buffering and decoding take time. You can't hear that delay when listening to music. For video, apps compensate by delaying the picture. In a game, or when playing an instrument, nothing can compensate for it.
SBC and AAC commonly run 150 to 250 ms. aptX Adaptive and LC3 get down to around 50 to 90 ms in their low-latency mode. Only proprietary 2.4 GHz links and a cable come in under 30 ms. The consequences for gaming are covered in gaming audio.
LE Audio, LC3 and Auracast: the new generation
The "classic" Bluetooth used for audio dates back to the early 2000s. Its successor, LE Audio, is built on the low-energy variant of Bluetooth and on a new mandatory codec, LC3. What it brings:
- Better quality at the same bitrate, which means more battery life for the same quality, or the other way around.
- A good-quality mic while you listen. Classic Bluetooth switches to a telephone mode, mono and muffled, the moment the mic turns on; LE Audio maintains decent sound in both directions.
- Auracast: broadcasting a single stream to an unlimited number of receivers. Sharing your music with a friend, or hearing the TV at the gym or the announcements at an airport in your own headphones.
- Support for hearing aids on the same footing as ordinary earbuds.
LE Audio is becoming standard on recent phones and headphones, but it requires both devices to support it. In the meantime, classic Bluetooth remains the common denominator.
What matters more than the codec
- Multipoint: staying connected to your computer and your phone at the same time. Invaluable for remote work.
- Connection stability: a modest codec that never drops out beats an ambitious one that makes the sound stutter.
- The headphones' internal processing: equalization, noise canceling and amplification weigh more heavily on the result than the way the signal is transported.
- A wired input: whether 3.5 mm or USB-C, it sidesteps the whole question, and saves a trip when the battery is dead.
Sources and references
Frequently Asked Questions
What is the best Bluetooth codec?
On paper, LDAC at 990 kbps and aptX Lossless offer the highest bitrates. In practice, AAC on iPhone and aptX Adaptive or LDAC on Android all deliver excellent results. The best codec is the one your phone and your headphones both support and that stays stable where you listen.
Does the iPhone support aptX or LDAC?
No. iPhones and iPads use only the SBC and AAC codecs. Headphones that support aptX or LDAC will work with an iPhone, but over AAC. Apple's AAC is very well implemented and is all you need for high-quality listening.
Does Bluetooth degrade sound quality?
It compresses the audio, with a theoretical loss. With a modern codec at a decent bitrate, that loss is inaudible to most listeners under normal conditions. The quality of the headphones, their tuning and their fit affect the result far more than Bluetooth compression does.