Bluetooth has been a blessing to the world as technology has pushed the world towards the wireless connection of electronic devices. Bluetooth connectivity is a regular thing now in music devices such as headphones. The constant advancement in Bluetooth versions, as well as audio compression codecs, has made it possible to transmit the audio signal without losing quality in the way.
In recent times, several audio codecs have flooded the market. While purchasing a Bluetooth audio device, the choice of audio codec is extremely important. This is because it literally determines the audio quality you can expect from the device. We will explain everything you need to know about Bluetooth audio codecs starting from the technical terminologies to different audio codecs.
What Is Bluetooth Codec?
A codec is basically a technology that compresses and decompresses data for faster and easier transmission. A codec has two components – an encoder to compress data and a decoder to decompress data. A Bluetooth codec decides how the data will be transmitted from the source, such as your smartphone, to the destination, such as your headphones via Bluetooth technology.
The main goal of a Bluetooth codec is to transmit high-fidelity audio signals at a minimum bit rate. This will help to transmit audio signals with minimum bandwidth and hence, at a faster speed. Similarly, the storage space and memory requirement for playback will be minimal as well.
Note: A low bit rate ensures greater compression with reduced audio quality. On the contrary, a high bit rate ensures lesser compression with better audio quality.
Why Do You Need A Codec In Bluetooth Audio Transmission?
In Bluetooth connectivity, you need a transmitter and a receiver. In this case, the Bluetooth audio transmitter is your smartphone, and the Bluetooth audio receiver is your headphone. The job of the transmitter is not just to send the audio file to the receiver. This is because sending the audio file in raw form wirelessly will exceed the bandwidth of Bluetooth connectivity.
Depending on the quality of the recorded audio, the file size is determined. High quality audio will end up as a large file size. On top of that, popular lossless audio file formats such as WAV and AIFF will ensure that file size stays large. Since Bluetooth connection has a limited bandwidth, the audio connection established through Bluetooth will start to stutter, and the audio quality will suffer. That is why there is the need for encoding and decoding, and that is where a codec comes into play.
How Does Bluetooth Wireless Audio Transmission Work?
A Bluetooth transmitter reduces the audio file size using an algorithm, and the audio file turns into a compressed file. This process is called encoding and is performed by an encoder of the codec. The compressed file is sent over to the Bluetooth receiver.
The compressed file is not a viable audio file, and hence, it needs to be decompressed. This decompression action is performed by a decoder of the codec. After decompression, the audio file becomes playable.
The codec is an algorithm that takes audio data, compresses them to reduce the size, encodes in a format for transmission. The same codec decodes the format on the receiver and makes the data playable for the user.
Every codec has its unique algorithm to compress audio data. Compression involves reducing audio data without reducing quality significantly. That is why there are various Bluetooth audio codecs available in the market. We will discuss them in detail in the following sections.
Terminology For Bluetooth Audio Codec
Before going into the different Bluetooth audio codecs, we need to discuss the related terminologies for your better understanding.
1. Sample Rate
This refers to the number of data points present in an audio file per second. In simple words, it refers to the frequency of the analog signal that is transmitted. It is measured in Hz.
2. Bit Depth
This refers to the number of bits per audio sample. It is a measurement of the audio resolution and quality. It is represented in bits. You will see DVDs giving 24-bit while CDs giving 16-bit.
3. Bit Rate
This refers to the number of bits processed per second. It is represented by the kilobits per second(kbps) or megabits per second(mbps).
4. Data Rate
It refers to the data transmitted per second.
5. Sampling Depth
It refers to the resolution of the audio data in the file.
It refers to the lag between the transmission and reception of the audio signal.
Different Types of Bluetooth Audio Codecs
1. SBC (Sub-Band Codec)
It is the most common codec you will find in almost all wireless headphones. However, its compression leads to heavy loss of audio quality. Its bit rate reaches a maximum of 345 kbps while its sample rate reaches a maximum of 45KHz.
The reason for the wide usage of SBC is that it is suitable for transmitting good enough audio quality at medium bit rate. Therefore, there will be no streaming issues, and the transfer rates will be easily manageable. The bottom line is that if a headphone comes with SBC only, the audio quality will not be superior.
2. AAC (Advanced Audio Codec)
You will find this codec on iPhones and iPads. It is compatible with Android as well. The codec supports 320 kbps bit rate at 24-bit depth and 96Khz sample rate. It uses a psychoacoustic model in its compression algorithm.
iOS device owners are recommended to purchase AAC-supported headphones for the best audio quality. The popular Bose Noise Cancelling Headphones 720 has this advanced audio codec and you know how powerful and high-quality audio output it produces.
3. AptX (Audio Processing Technology)
The codec is designed by Qualcomm, and it ensures better audio quality. You will find it under different labels such as AptX, AptX HD, AptX LL. They have different bit rate, sample rate, and bit depth.
In AptX HD, the maximum bit rate is 567 kbps with sample rate of 48 Khz and bit depth of 24-bit. In AptX, the maximum bit rate is 384 kbps with sample rate of 48 Khz and bit depth of 16-bit. However, both of them have latency of 170 and 270 milliseconds, respectively.
This latency problem is solved in AptX LL where the latency is reduced to 40 milliseconds only. If you opt for a gaming headset, you should have low latency and hence, AptX LL is a better codec choice. However, Apple does not support AptX LL.
4. AptX Lossless
AptX Lossless is one of the latest codecs designed by Qualcomm. It was released in the second half of 2021. It offers a sample rate of 44.1KHz at 16-bit depth. It is perfectly suitable for premium audio streaming as the loss of audio quality is minimal. However, the source and the destination need to support the codec to make it function properly.
5. AptX Adaptive
AptX Adaptive came out as the successor of AptX, but it has not achieved the popularity as expected. You will find the codec in selected headphones only. It is better than AptX, and you have various advantages over the other AptX versions.
The latency is relatively low, and hence, it is suitable for gamers and movie watchers. It can achieve a maximum bit rate of 420 kbps, and the latency is around 80 milliseconds. The codec has backward compatibility as well.
6. LDAC (Lossless Digital to Analog Converter)
The codec is designed by Sony, and they are a pioneer in the audio device industry. The codec focuses on reducing the loss of audio quality during transmission and streaming. The maximum bit rate is 990 kbps with a sample rate of 48KHz and a bit depth of 16 bits.
There are loads of devices that support LDAC codec, and you get true HD audio quality. However, if you use it on an Apple device, you will not notice the quality differences because the bit rate is toned down automatically.
There are three different modes available – 990 kbps, 660 kbps, and 330 kbps. By default, smartphones use 330 kbps, but you can upgrade it to the other two options. You have to use high-end headphones to get the best of LDAC.
7. LHDC (Low-Latency and High-Definition Audio Codec)
This codec is present in some high-end headphones, such as the OnePlus Buds Pro. The maximum bit rate is 900 kbps with a sample rate of 96KHz and bit depth of 24 bits. Even though it has very low latency, it is yet to make a widespread application except for flagship headphones.
The latest Bluetooth version comes with LC3 codec, which ensures superior audio quality at a low sample rate. It is a dream come true codec for audio geeks. You can consider this to be the latest Bluetooth audio codec in the market.
The codec will be delivering audio to people using hearing aids that are Bluetooth-enabled. They can stream any audio and still be aware of their surroundings. You can stream audio to multiple Bluetooth devices from a single source.
Comparison Among Different Codecs
|Codec||Max Bitrate||Bit Depth||Sample Rate||Introduced Year|
|SBC||320 kbps||16 bit||48.0 kHz||2003|
|AAC||264 kbps||16 bit||44.1 kHz||2015|
|aptX||352 kbps||16 bit||48.0 kHz||2009|
|aptX HD||576 kbps||24 bit||48.0 kHz||2016|
|aptX LL||352 kbps||16 bit||44.1 kHz||2016|
|LDAC||990 kbps||24 bit||96.0 kHz||2015|
Buying a Bluetooth-enabled audio device with the latest codec may not always be the right choice. This is because compatibility is important, and the source device should not tone down the audio parameters automatically. Therefore, you should always aim for optimal audio quality with less important parameters for your understanding and easy decision-making.