Audio quality via a Bluetooth device can be a great mystery, partly because Bluetooth only mandates in its basic audio standard, A2DP (Advanced Audio Distribution Profile), a low-quality audio encoding algorithm. An audio encoder takes a data stream and transforms it into whatever the best or agreed-upon quality both sides can take, often limited by the particular chips on each device and bandwidth available.
That means that the lowest-common denominator may prevail, even when both the sending and receiving devices have a variety of higher-quality options available that don’t match up or aren’t correctly invoked.
Depending on a host of factors, both a Bluetooth streaming device (sending or receiving audio) and a Mac may agree on an encoder that makes music sound like it’s playing over a landline telephone call.
That shouldn’t happen, because iPhones, iPads, and Macs have offered high-quality encoders for many years that are compatible with a wide range of Bluetooth audio equipment from third parties, as well as Apple and Beats hardware. But we’ve heard from readers and found discussed repeatedly online problems getting the best results on a Mac. This happened in my house just the other day, when my trombone-playing older kid was having a Bluetooth mic peak out—the sound overwhelmed the mic—when he was trying to record himself.
The answer is complex. So much so that someone with the handle ValdikSS had to devote thousands of words in a well-illustrated article at Habr to do justice to the details.
The long and the short is that some integrated devices that couple a mic with a speaker or earphones—as in earbuds, headphones with mic input, a headset with a projecting mic, or a speakerphone—can force audio quality way down when paired with a Mac and with some other hosts.
As ValdikSS notes, this duplex mode of sending and transmitting simultaneously is a problem. “When this mode is used, both the voice from the microphone and the audio are transmitted to the headphones with the same quality…Unfortunately, as of 2019, the quality of voice transmission via Bluetooth is still poor, and it is not clear why Bluetooth SIG is not doing anything about it.” (The SIG is the trade organization that sets standards and runs certification problems.)
Not all Bluetooth audio in/out combinations drop in quality, though. So you may not have encountered this with a device you use. Or you may not know, as the sound you hear from others could be higher quality than the compressed sound they hear from your mic. You might need to record sound from your device or have someone record it on their end to see how good or bad it sounds.
Unfortunately, the only solution in most cases is to switch to a USB-based headset or USB mic and headphone combination. That ensures the best quality audio is used on your Mac. Some devices may have both Bluetooth and USB options, in which case you can use the USB connection when you need to get higher-quality audio input. That’s what my kid did: the same mic input connected via Bluetooth captured the whole dynamic range of his trombone piece.
If you’re having trouble with the quality when playing sound back, whether your Bluetooth device has a mic or not, you can try these tricks.
Select a different audio input device in the Sound preference pane’s Input tab and in any software you may be using that lets you select audio input. This may prevent a poorer audio encoder from being used.
Check whether your device when connected is using a lower-quality encoder by pressing Option while selecting the Bluetooth menu in the system menu bar and viewing the menu for that device. This article at How-To Geek provides the extensive steps to use a developer app from Apple to force a higher-quality encoder.
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