LDAC vs aptX vs AAC: how Bluetooth audio codecs compare

Why Bluetooth audio is compressed

Uncompressed CD-quality stereo needs about 1,411 kbps of steady throughput, more than a Bluetooth audio link can hold reliably. So the phone encodes the music, nearly always with a lossy codec, sends the smaller stream, and the headphones decode it before their own DAC and amplifier play it. Everything you hear from a wireless headphone has passed through that encoder, whatever the file you started with.

Two rules decide what you get. Both ends must support a codec for it to be used, so the connection settles on the best one the phone and the headphones have in common. And the higher-bitrate modes need a strong, clean radio link. When the signal weakens, an adaptive codec drops to a lower bitrate, and a fixed one starts to break up.

SBC, the codec every device shares

SBC, or Sub-Band Coding, is mandatory in every Bluetooth audio device, so it is what you get when the two ends share nothing better. At its highest standard setting it runs at about 328 kbps and sounds reasonable. Many devices use lower settings, where its compression becomes easier to hear.

Cheap devices often stop at SBC because other codecs carry license fees. The review of the $29 SMSL PS100 counts its Bluetooth input's lack of better codecs as a con, and puts it down to exactly those licensing costs.

AAC and the iPhone

AAC is the codec family behind Apple Music and several streaming services, standardized by ISO/IEC. iPhones and iPads send AAC over Bluetooth at around 256 kbps, and Apple's encoder is good enough that most listeners find it hard to tell from the source on most music. On Android, results vary more with the phone's encoder.

iPhones support neither aptX nor LDAC. Pair one with an LDAC or aptX headphone and the link runs on AAC, so for iPhone owners the AAC support matters more than the headline codec. The HIFIMAN Svanar Wireless, for example, supports LDAC, AAC and SBC, and would run AAC from an iPhone.

The aptX family and its versions

Qualcomm's aptX codecs are common on Android phones, headphones and receivers. Standard aptX carries 16-bit audio at 384 kbps at 48 kHz. aptX HD raises that to 24-bit at 576 kbps. aptX Adaptive changes its bitrate with radio conditions and adds a low-latency mode for video and games, and the newest Snapdragon Sound devices can carry CD-quality lossless audio when the link allows.

The family is only as good as the chips at both ends, so "aptX" on a box needs checking against which version. The Fosi Audio ZD3 DAC lists aptX HD on its Bluetooth input, and the SMSL RAW-MDA1 takes LDAC, aptX and aptX HD, SBC and AAC. Its review points out that none of them is lossless.

LDAC and its three bitrates

LDAC was developed by Sony and has shipped with Android since version 8. It runs at 330, 660 or 990 kbps, and at 990 kbps it has the highest bitrate of the lossy codecs here, carrying up to 24-bit/96 kHz. It is still lossy at every setting. The Svanar Wireless review makes that point and judges it unlikely to be a significant concern with wireless in-ears.

Many phones default to an adaptive mode that picks the bitrate for connection stability, so LDAC headphones in a busy street often run far below 990 kbps. Developer settings on most Android phones let you force the highest rate, at some cost in range and battery. The OneOdio Max 1 is a €179 over-ear with LDAC over Bluetooth 5.3, and its review found the wired connection a touch cleaner still. A headphone's wired and wireless modes can run through different electronics, though, so the codec isn't the only thing that changes.

When the codec makes a difference

Less often than the marketing suggests. The gap between a good AAC or aptX stream and LDAC is small, and it shows mainly on a resolving headphone, with a good recording, in a quiet place. The tuning of the headphone, its fit and seal, and the processing inside it (EQ, noise canceling, the built-in DAC and amplifier) change the sound more than the codec does.

The codec matters most in three cases. The first is when you're stuck on SBC because your phone and headphones share nothing better. The second is latency for video, games or performance, where some products skip Bluetooth: the Max 1's DJ mode runs through a separate M1 transmitter at 20 ms. The third is a Bluetooth input on a hi-fi DAC, where the wireless link can be the weakest part of an otherwise good chain. For critical listening a cable remains the only path that is always lossless. The IEM guide ranks wired and wireless in-ears side by side, and the IEM explainer covers how the designs differ.