The Bluetooth codec your headphones use has a significant impact on sound quality. Unfortunately, macOS sometimes uses the below-average SBC codec instead of the superior aptX or AAC codecs. Here's how to force macOS to use one of these codecs.
What is a Bluetooth codec?
The word "codec" stands for "codec decoder". That's exactly what a codec does. In this case, the codec is used to compress the audio file at one end (code) and decompress it at the other end (decode). This allows the file to be transferred quickly. Some codecs can compress audio better than others without affecting quality, so choosing the right codec is crucial.
SBC is the codec that macOS sometimes uses by default, while aptX and AAC offer better sound quality. All three codecs compress the audio before you send it to your headphones, but aptX and AAC do so without dramatically affecting overall audio quality. SBC is designed to be efficient and ensure compatibility rather than providing the best possible sound quality. Latency also plays a role in SBC, and there is an audio delay when watching video content. Neither aptX nor AAC show this behavior.
If you want to learn more about how aptX and AAC work, we have a good introduction to this topic.
In short, aptX promises a "CD-like" sound quality that SBC can not offer. Similarly, AAC's improved compression algorithms provide better sound quality, though the maximum bitrate of 250 Kbps is lower compared to the 328 Kbps of SBC. However, the aptX codec surpasses both with 352 Kbit / s.
Unfortunately, not all Bluetooth headsets support aptX or AAC, though most newer models do. If you force your Mac to use one of the two codecs but your headphones do not support it, it automatically switches to SBC.
RELATED: What is the difference between Bluetooth A2DP? and aptX?
How to check which codec to use
To determine which codec to use, connect your Bluetooth headphones to your Mac and play some audio. Hold down the Option key and click on the "Bluetooth" icon in the menu bar.
Highlight your headphones and make a note of the active codec.
This is the currently used codec. You're fine if it's aptX or AAC. Otherwise, read on.
How to Force aptX or AAC
Download additional tools for Xcode from the Apple Developer Site. You will need to create a free Apple Developer account. After downloading, double-click the DMG Additional Tools file to attach it.
Double-click Additional Tools on your desktop.
Click the Hardware folder.
Drag "Bluetooth Explorer.app" to your Applications folder.
Double-click Open the Bluetooth Explorer app and on the menu bar, click Tools> Audio Options.
Select the Force aptX and Enable AAC check boxes. Make sure the Disable AAC and Disable aptX check boxes are cleared. (Yes, for some reason, you can use the app to enable both the Enable and Disable check boxes.)
Click the Close button to save the changes.
Disconnect and reconnect to your headphones. Then make sure you are using the previously described aptX or AAC codecs. In this case, you should notice an improvement in sound quality. If not, you may want to treat yourself to some new headphones.