Music from the phone is transmitted to the earbuds via Bluetooth.
In order for that transmission to work, and in order for the devices to understand each other, the phone and the earbuds must use the same language. That language is the codec that both sides use. Only then can the music be compressed, packaged from the phone to the earbuds, and then decompressed so it becomes sound that can actually be heard through the earbuds.
Besides phones and earbuds, there are music players, Bluetooth speakers, sound systems, and cars. But to keep this article short and clear, the phone is used as the music source and the earbuds as the receiving device.
For example:
- You play an MP3 file on your phone using Bluetooth earbuds that support LC3.
- The phone decodes the MP3 file into PCM (Pulse Code Modulation) data.
- The LC3 codec compresses the PCM data into an LC3 stream.
- The LC3 data is transmitted over Bluetooth to the earbuds.
- The earbuds decode LC3 back into PCM, then use a DAC to convert it into an analog signal to produce sound.
Bluetooth Codecs on iPhone: What Actually Happens
On iPhone, Bluetooth audio works in a very simple and controlled way. The system uses AAC as the default codec, and everything related to Bluetooth audio is handled automatically, without giving the user the option to choose or change codecs manually. Even if the earbuds support more advanced codecs like LDAC or aptX, the iPhone will still transmit audio using AAC or SBC, because Apple locks the experience in order to control stability, battery usage, and compatibility across devices.
AAC as the Default Codec
AAC is the default Bluetooth audio codec on iPhone.
This codec allows music, videos, and other audio to be transmitted with stable quality and relatively low power consumption. AAC is used as the main codec for Bluetooth audio on iOS devices.
Why There Is No LDAC or aptX
iPhone does not support LDAC or aptX codecs.
Even if the earbuds support these codecs, the iPhone will still use AAC or SBC. This means that advanced codecs available on the earbuds cannot be used on iPhone.
Why Apple “Locks” the Experience
Apple locks the Bluetooth audio experience so the system can control stability, battery usage, and compatibility. The user cannot manually select codecs or force higher-quality modes. Everything is handled automatically by the system.
Bluetooth Codecs on Android: More Options, More Variables
On Android, Bluetooth audio behaves differently and offers more options.
SBC as a Fallback Codec
SBC is the mandatory Bluetooth codec on Android.
When no higher-quality codec is available, or when the connection becomes unstable, the system falls back to SBC automatically.
AAC on Android Is Not Always the Same
AAC exists on Android, but it does not always behave the same way.
Depending on the phone, AAC can sound different because of system optimization, Bluetooth chip quality, and software implementation.
LDAC, aptX, and Adaptive Codecs
Android supports codecs like LDAC, aptX, aptX HD, and aptX Adaptive.
When both the phone and the earbuds support the same codec, higher-quality audio transmission is possible.
Why Two Android Phones Don’t Sound the Same
Even when using the same earbuds, two Android phones can sound different.
This happens because of differences in Bluetooth chips, audio processing, system tuning, and software layers.
Is It the Codec or the Phone That Changes the Sound?
Many people think that Bluetooth sound quality depends only on the codec. In reality, the codec only defines how audio data is compressed and transmitted, but before and after that there are other steps that affect the final sound.
When you play music on the phone, the phone first decodes the music file into PCM (Pulse Code Modulation). Only after that does the Bluetooth codec compress the PCM data into a codec stream that can be sent wirelessly to the earbuds.
That codec stream is transmitted over Bluetooth to the earbuds. On the earbuds side, the codec stream is decoded back into PCM, and then the DAC converts the PCM signal into an analog signal so sound can be played.
Because of this, sound quality does not depend only on the codec itself. The phone is part of the process, the decoding stage is part of the process, and the conversion back to analog sound is also part of the process.
Conclusion: the codec matters, but it is not the only thing that changes how Bluetooth audio sounds.
Why You Usually Can’t Choose the Bluetooth Codec
In real usage, users usually cannot choose which Bluetooth codec is being used. The system automatically selects the codec so the connection can work properly.
The system prioritizes stability over quality. If the signal is not stable, bitrate is reduced or the system switches to another codec to keep audio playing without interruptions.
On Android, developer options exist and allow users to see or select codecs. However, in practice this often does not help because the system can override that choice at any moment if it detects instability.
On iPhone, codec selection is fully automatic and hidden from the user. Users cannot choose codecs or change how Bluetooth audio is transmitted.
Latency, Stability, and Battery: iPhone vs Android
Latency is the time between when the phone sends audio and when the earbuds play sound. Latency is measured in milliseconds.
Lower latency improves audio and video synchronization, which is important for watching videos or playing games. When listening to music, latency is not important.
Different codecs have different latency values. Some codecs focus on sound quality, while others focus on reducing latency.
Battery usage is also affected by the codec. Higher bitrate and more complex codecs usually consume more power on both the phone and the earbuds.
In environments with many wireless signals, such as Wi-Fi networks and other Bluetooth devices, stability becomes more important than quality. In these situations, systems often lower bitrate to keep the connection stable.
So Which One Sounds Better in Real Life?
Different codecs are designed for different goals. Some aim for better sound quality, others aim for lower latency or better stability.
Understanding Bluetooth codecs helps users choose the right phone and earbuds for their needs. Choosing the wrong combination can result in poor experience and wasted money.
iPhone offers a stable and consistent Bluetooth audio experience.
Android offers more options, but results can vary.