SBC, AAC, LDAC & AptX: HD Bluetooth audio codecs explained

 SBC, AAC, LDAC & AptX: HD Bluetooth audio codecs explained

When your phone sends music wirelessly to your headphones or speakers, it compresses the audio for transmission over Bluetooth. A few years ago, this meant a notable reduction in audio quality, but today, newer compression techniques are available which allow lossless CD-quality sound to be sent wirelessly. These compression techniques are known as codecs.

The first Bluetooth headphones used the SBC codec, which is still universally supported by all devices and often delivers acceptable quality. If you’re using some decent quality speakers though you’ll notice the improvement in quality offered by the AptX codec, and if you’ve got some really high-end kit you’ll definitely want to use AptX HD or LDAC for the best possible sound.


SBC

SBC, short for low complexity sub-band codec, is the standard audio codec supported by all Bluetooth audio devices. It’s what ensures pretty much any Bluetooth speaker or headphones will work with any phone regardless of the which of the codecs below are available, as the devices will automatically fall back to SBC if no other codecs are mutually supported.

The quality is good enough for many uses, and even for music, on low-end headphones or speakers, or in a noisy environment, you might not notice any improvement from using a higher quality codec.

SBC bitrates over Bluetooth vary from 192Kbps to 320Kbps.

Advantages

  • Universally supported by all A2DP Bluetooth audio devices

Disadvantages

  • All other codecs offer better quality, with the exception of AAC on some Android phones

AptX

AptX was developed by Qualcomm and is supported by most modern Android devices, in addition to Windows 10 and Macs computers. It’s widely supported by loads of audio devices, including low-end wireless headphones, so unlike some other codecs, you don’t need to purchase expensive equipment to take advantage. It’s been around a while and was the first widely supported codec to improve on the standard SBC quality.

AptX has a maximum bitrate of 352Kbps and supports audio up to 48Khz at 16-bit quality.

Advantages

  • Higher quality audio than the SBC or AAC codecs
  • Widely supported by inexpensive audio equipment and Android devices

Disadvantages

  • Not supported by Apple iPhones or iPads
  • Newer codecs like AptX HD and LDAC offer better quality and HD audio

LDAC

LDAC was developed by Sony and is the only codec which promises to transmit 16-bit 44.1Khz CD-quality audio completely untouched, in addition to supporting a maximum quality of 24-bit 96Khz. This is higher than any other Bluetooth audio codec, and it also has the highest maximum bitrate at 990Kbps. It’ll also function at 660Kbps and 330Kbps depending on signal quality.

LDAC features extensively in Sony’s high-end audio equipment, like their popular WM-100XM3 headphones. Most modern Android devices offer native LDAC support. The quality offered makes it the codec of choice for many audiophiles and high-end users.

Advantages

  • The best quality and highest bitrate of any Bluetooth audio codec
  • Supported by most modern Android devices
  • Supports high-resolution sound up to 96Khz at 24-bit

Disadvantages

  • Not supported by Apple iPhones or iPads
  • Only works on Windows with an external DAC
  • Generally only supported by high-end Sony headphones

AAC

AAC, short for advanced audio coding, is probably the most widely-supported Bluetooth codec other than the standard SBC, thanks to Apple’s decision to include support for the codec in all their modern iPhone and iPad devices.

Most devices support bitrates up to 250Kbps when using AAC over Bluetooth, streaming 16-bit quality audio at 24Khz.

It’s been suggested that music streamed or downloaded in AAC format can be sent via an AAC Bluetooth connection without being recompressed, preserving quality. However, this has never been shown to happen in the real world.

Advantages

  • Higher quality than the standard SBC codec
  • Supported by iPhones, iPads and Macs, in addition to all modern Android devices
  • Widely supported by audio devices, including the popular Bose QuietComfort 35 II

Disadvantages

  • No support for CD-quality or HD audio, unlike other Bluetooth codecs
  • More CPU-intensive than SBC or AptX, leading to higher battery usage and increased latency/delay.
Bluetooth audio codec AAC headphones
The Bose QuietComfort QC II notably support no codecs better than AAC

AptX HD

An updated version of AptX was released by Qualcomm in 2016, called AptX HD. This ups the bandwidth to 576Kbps from the 352Kbps used by classic AptX. It also adds support for 24-bit, 48Khz high-resolution sound.

AptX HD also supports what Qualcomm calls ‘CD-like’ audio quality streamed at 16-bit, 44.1Khz. It was sometimes called ‘AptX Lossless’ but the term has now pretty much dropped out of usage.

Advantages

  • Supported by a wide range of audio devices and most modern Android phones
  • Offers ‘CD-like’ audio quality when streaming 16-bit, 44.1Khz audio
  • Supports 24-bit high-resolution audio at up to 48Khz

Disadvantages

  • LDAC offers slightly better quality and a higher maximum sampling rate of 96Khz
  • Not supported by iPhones or iPads

AptX LL

AptX LL, short for AptX Low Latency, is a specialist version of the AptX codec with minimal latency or delay. This makes it perfect for using wireless headphones to watch TV or movies, as the delay incurred by other codecs can throw the lip-sync totally out to the point it’s unwatchable.

Other Bluetooth audio codecs can experience well over 300ms of latency, well beyond the 40ms limit recommend for seamless TV viewing. AptX LL reduces the latency of the Bluetooth transmission to just 32ms

You’ll need to make sure your headphones specifically support AptX LL, as not all AptX devices do, and you’ll probably also need to pick up an AptX LL Bluetooth transmitter and plug it into your TV.

Advantages

  • Massively reduced latency (around 90% lower than other codecs) makes AptX LL suitable for TV, movies and gaming
  • Supported by a wide range of inexpensive Bluetooth transmitters

Disadvantages

  • Rarely supported by phones or computers
  • Limited headphone support
  • Lower sound quality than AptX HD, AptX Adaptive or LDAC

AptX Adaptive

The latest version of AptX, dubbed AptX Adaptive, combines the best features of AptX HD and AptX LL. It uses a variable bitrate between 280Kbps and 420Kbps depending on signal conditions and claims compression improvements mean it matches the quality of 576Kbps AptX HD despite the reduction in maximum bitrate.

AptX Adaptive can also switch into a low latency mode, like AptX LL, when required, making it suitable for use watching TV or movies. It’s not quite at fast as AptX LL’s 32ms and clocks in at about 50ms, but it’s unlikely you’d notice the difference.

Advantages

  • Matches the quality of AptX HD
  • Automatically switches to low-latency mode for watching TV or similar
  • Automatically reduces quality/bandwidth when conditions demand to avoid interruptions
  • Supports high-resolution audio up to 96Khz at 24-bit

Disadvantages

  • New codec with limited device support, though expect this to improve
  • No sign of iPhone or iPad support
  • Slightly higher latency than AptX LL with limited availability of Bluetooth transmitters for TVs etc
  • LDAC offers improved audio quality

LDHC / HWA

LDHC, also known as HWA, is similar to Sony’s LDAC. It’s only recently been introduced and was mostly supported by Huawei phones, but has been included in Android by default since Android 10. Like LDAC, it offers support for 24-bit sound at 96Khz and operates on three different bandwidths depending on conditions; 400Kbps, 560Kbps and 900Kbps.

Some LDHC devices also support LLAC or LDHC LL, a low-latency mode with a claimed delay of around 30ms. This would make it marginally faster than the 32ms of AptX LL. The HWA association certify devices that meet minimum performance standards when implementing LDHC.

Advantages

  • Supported by recent Android devices
  • Could match the quality of LDAC
  • Auto-switches to very fast low-latency mode

Disadvantages

  • Limited audio device support
  • No sign of iPhone or iPad support

CVSD & mSBC

CVSD and mBSC are used for phone calls. When you’re using headphones or a speaker to play music, and a phone call comes in, devices that also allow you to take calls will switch from Bluetooth’s audio playback mode, A2DP, to the hands-free calls mode known as HFP.

CVSD and mSBC can only be used with HFP, while all the other codecs above are used within A2DP for music and other audio playback.

Sam Warrenger

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