When you buy new wireless headphones, the specifications table may contain abbreviations that are unknown to many people. For example, AAC or aptX. They are needed to transmit sound «over the air» from your smartphone or laptop to potential headphones. In this article, we will analyze the most common audio codecs.
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An audio codec is a software application that encodes and decodes audio data. In simple terms: «opens and closes the doors of» audio information received from your device or application (e.g. Poweramp, Spotify, or Youtube). You need to be careful here, because this codec does not directly transmit data from your device to wireless or wired headphones.
Kodek is an acronym for the words coblowing and deckairing.
Sound wave: analog and digital.
There are two types of audio codecs: software and hardware. In most cases, software codecs are built into the applications we are used to listening to audio and watching videos: Winamp, K-Lite Codec Pack, and others.
Back in the old days of Windows 98 and earlier, when common standards for video and audio were just being established and introduced, a user could easily encounter an audio file and not hear what was playing in it. There were even more problems with video: the inability to play the audio track, the video itself, or even both components. Nowadays, such problems are almost non-existent.
A hardware audio codec is a separate chip inside your device that encodes and decodes an analog signal into a digital signal and vice versa, using a DAC (digital-to-analog converter) and an ADC (analog-to-digital converter). A common example of such a codec is the — High Definition Audio motherboard from Realtek.
The characteristics of codecs are: Frequency Range and Sampling, Bit Rate, Bit Rate. So let’s talk about each of them separately.
The frequency range is perhaps the most understandable of all the above characteristics. As the name implies, these are the supported frequencies for audio playback. The human ear can hear within the range of 20-20000 Hz. Therefore, codecs can remove «unnecessary» recorded data (before and after 20 kHz) not only to reduce headphone power consumption, but also to reduce file size.
The Sample Rate is a bit more complicated, as its main task is to convert a continuous signal into a discrete (divided) one. The higher the frequency, the better. For example, 16 kHz sampling is used for voice calls, while 192 kHz is used for movies on Blu-ray discs.
Audio Bit Depth is quite simple to explain: how many bits are used to record one sample after the signal is sampled. For obvious reasons, the higher the bit depth, the better the sound. There are 8 (28 = 256 values within one sample), 16 (216 = 65536) and 24 bit (224 = 16 777 216).
Bitrate reflects the data flow — how many bits are transmitted per second of time. It is measured in kbps. It is a combination of the previous characteristics. For example, a bitrate of 128 kbps means that 128 thousand bits are required to encode one second of a melody. The higher the bitrate, the better. That’s why you need 246 kbps and higher to listen to music, although for podcasts, 128-196 kbps will be enough.
After receiving the audio data, the main work of codecs is to compress the information for processing and further listening to music or podcasts. Codecs are divided into two types according to the type of compression:
As you can see from the simple translation of the words, for codecs with the Lossless compression principle, audio information is stored without loss of quality. That’s why audiophiles love it. Because of this, tunes can take up a lot of space on a disk/phone. For example, audio in FLAC format will take up approximately 45-60 MB of memory. Ordinary people may be intimidated by the size of just one song. Therefore, using Lossy compression in the mp3 format (5-10 MB) will allow you to save more disk space.
The main problem with Bluetooth codecs is that they cannot transmit the full recorded quality. Even if you open songs on your smartphone/PC in FLAC (Free Lossless Audio Codec), the quality of the transmitted sound in the headphones will be lower.
Of course, we would like to always have perfect sound at any time and on any device. Progress is not stagnant, but it is still not enough to deliver «perfect sound» for one reason — it is technically difficult to process 96 kHz, 32 bit at 6144 kbps. Even if you take a 44.1 kHz, 16-bit, 1200 kbps FLAC file, it will weigh 40 MB. This may seem like a lot. But if you take the same song at 96 kHz, 32 bits, you’ll get more than 200 megabytes!
To transmit sound over the air, TWS headphones use the familiar Bluetooth of various versions. However, its maximum bandwidth may not be enough even for FLAC:
| Bluetooth version | Maximum throughput |
| Bluetooth 4.0 | up to 1 Mbps (1024 kbps) |
| Bluetooth 5.4 | up to 2 Mbps (2048 kbps) |
| Bluetooth 6.0 | up to 3 Mbps (3072 kbps) |
And this is data from tests in a «ideal world». In the real world, this data will be less. Although with the release of Bluetooth 6.0, there is already a chance of full use of FLAC (about 1400 kbps) without any problems for transmission. It remains to wait a few years for the appropriate devices to support it. Just don’t forget about the delays that occur at various points in audio processing or transmission. This is especially true when used in gaming.
Let’s move on to popular codecs that can be found in most TWS headsets.However, withTo begin with, here is a general comparison table of codecs.
| Codex | Type | Bitrate (kbps) | Frequency (kHz) | Bit depth (bits) | Delay (ms) |
| SBC | Lossy | up to 345 | 44.1 / 48 | 16 | 200-250 |
| AAC | Lossy | 128-256 | 44.1 / 48 | 16 | 150-200 |
| aptX | Lossy | 352 | 48 | 16 | 100-150 |
| aptX HD | Lossy | 576 | 48 | 24 | 150-200 |
| aptX Adaptive | Lossy | 276-420 | 44.1 / 48 | up to 24 | 50-80 |
| aptX Low Latency | Lossy | 352 | 44.1 / 48 | 16 | 40 |
| aptX Lossless | Lossless | up to 1200 | 44.1 | 16 | 80-100 |
| LDAC | Lossless | up to 900 | 44.1 / 48 / 96 | up to 24 | 100-200 |
First, let’s talk about codecs with «loss» (Lossy). Codec SBC (Subband Codec) is one of the most common codecs for TWS headsets. Not the best sound quality at high frequencies. This codec is often used to transmit the user’s voice during a voice call.
Codex AAC (Advanced Audio Codec) provides better sound quality at the same bitrate than SBC. This codec is used by Apple for all its devices. The main disadvantage is the increased power consumption of the processor for the operation of this codec.
Codex aptX is an average option with no obvious disadvantages or advantages. It was developed by Qualcomm. There are many implementations of this codec for different needs:
As you can see, there are many Lossy standards. But what about codecs «Lossless» Lossless. And here there are only two standards:
Codec LDAC (Lossless Digital Audio Codec), although it contains the word Lossless, is not exactly that. The bitrate can be between 330, 660, and 990 kbps. A stable Bluetooth connection is required to unlock the potential. In addition, you need to have Sony devices, as it is the developer of this codec.
Codec aptX Lossless with support for 1200 kbps bitrate, i.e. CD-quality (16 bit/ 44.1 kHz). Bluetooth version 5.2 or higher is required.
Nowadays, there are a lot of codecs available. However, you don’t need to worry about this when buying Bluetooth headphones or headsets. They support the same audio standards as smartphones or PCs. Therefore, most users do not need this information. But for those who want to better unleash their audio potential, it is necessary to wait for the next iteration of technological progress to fully utilize wireless headphones.