Under ideal conditions (no transmission errors/retransmissions), Bluetooth can theoretically transmit up to ~1.5Mbps of streaming data (assuming all time slots are filled with 2-DH5 packets). In reality, however, radio signals are distorted by interference and data needs to be retransmitted. As a result, the effective bitrate is much lower. If you try to use high bitrate CODEC settings (such as SBC with a bitpool higher than the device's maximum bitpool, aptX-HD, LDAC with HQ/SQ quality), you may be sending more packets than your setup can handle. As a result, you may experience the following problems:
- Choppy sound.
- Audio latency increases over time.
- Connection may be lost unexpectedly.
- The right/left sound of the TWS headphones may be out of sync.
- Volume control stops working.
In addition, if you are using the aptX Low Latency CODEC, your headphones will operate with very little buffering, and despite its relatively low bitrate usage, it can be very sensitive to delays in radio packet transmission, and you may hear pop noise or choppy sound when packet transmission is delayed.
If you are experiencing these symptoms, you may need to check the following factors:
- Minimize radio interference to reduce the retransmission
- Do not use 2.4GHz radio, such as 2.4GHz WiFi
Use 5/6GHz WiFi or wired Ethernet instead.
- If you have to use 2.4GHz WiFi, consider using a WiFi/Bluetooth combo adapter instead of separate adapters
WiFi and Bluetooth adapters communicate with each other and minimize interference in a combo adapter. They do not communicate with each other if you use separate adapters and cause more interference.
- Use high transmission power Bluetooth adapter
Bluetooth devices are classified into three power classes. Most Bluetooth adapters used for PC are either Class 1 (high power) or Class 2 (medium power). A Class 1 adapter gives you a more stable connection at a high bitrate. As of this writing, there is no easy way to tell if your adapter is Class 1 or Class 2, but here is a rule of thumb:
- Maximize the time slot used by other Bluetooth devices
If you connect other Bluetooth devices, such as a keyboard, mouse, and touchpad, they eat up the time slots that can be used for audio streaming. The amount of data those devices send is relatively small, but their impact is not negligible as they send the data frequently.
Those devices may need to be turned off while high-bitrate audio streaming is happening to free up the time slots usable for audio streaming. (Or, if you use the high-bitrate audio streaming regularly, you may want to consider switching to the mouse/keyboard that uses non-Bluetooth wireless technologies.) Please note that those devices still consume timeslots while they are idle as long as they are connected to your PC.
- TWS specific issues
Last but not least, TWS headphones are not good at receiving high-bitrate streams. You usually start hearing choppy sounds at a lower bitrate compared to regular headphones. This is because:
- Due to their smaller size, they don't have good antennas. It causes more data corruption and ends up with more re-transmission.
- Earbuds need to communicate with each other, and that is done using the Bluetooth time slots otherwise used to receive the streaming packets.
For example, LDAC HQ (990kbps) with TWS is not impossible, but for that to work without choppy noise, you need to clear all other issues listed above.
- Multipoint
If multipoint is properly implemented, the connection of another device should have little effect on the stability of the streaming. However, some headphones do not properly implement multipoint, and the activity between the headphones and another device (even if it is a seemingly small activity) can significantly limit the maximum bitrate of the streaming. You may not notice this problem if you are streaming at a low bitrate (such as ~300kbps), but it can be a significant problem if you are streaming at a high bitrate. To see if this is the case, please do the following:
- If the phone app for your headphones has an enable/disable control for the multipoint feature, disable it. (preferred method)
- Otherwise, turn off the Bluetooth radio on the other device.
and see if this improves streaming stability. If it does, it means that your headphones' multipoint implementation is not optimal. Your choice is to either avoid multipoint or reduce the bitrate/encode quality mode (manually or automatically by enabling ABR).
- Device driver for the Bluetooth adapter (dongle)
Sometimes the device driver of the Bluetooth adapter can affect the streaming stability. Apparently, because the standard Windows A2DP driver only uses up to ~300kbps bitrate, adapter drivers are only tested with such low bitrates. They may have problems with higher bitrates like 990kbps. And in our experience, newer versions aren't always better than older ones.
So please start with the latest driver version. If it doesn't work well, please try some older versions. Please also note that Bluetooth adapter drivers are often automatically updated by the Windows Update. So if you find a driver version that works well for you, please keep it. You may want to reinstall it later.
If the problem persists after checking all of the above, you probably need to change the CODEC settings to lower the bitrate.