HBS-700 sound quality on Mac OS X

I was recently looking for a pair of Bluetooth headphones to isolate myself from the world without a cord tethering me to my laptop. I ended up settling on LG’s HBS-700 headphones due to spectacular reviews on Amazon. The cost of selecting the HBS-700, rather than its newer cousin, the HBS-730, was missing out on the apt-X codec, which is reportedly much better than the standard SBC codec that most Bluetooth devices use. But the HBS-730 noted terrible range and poor reliability, which really doesn’t work for me when I’m shipping these headphones 12 timezones away from the retailer. So I chose the HBS-700.

Despite the occasional typo in the user manual (yes, I do read user manuals for fun), first impressions of the device were pretty good. The device is light, well-built, and comes with a charge. The only problem I noticed was that sound quality was substantially lower than my cheapo Acoustic Research ARE-09s. Turns out that there is an easy fix for this; disconnect the headset, open Terminal and run this:

defaults write com.apple.BluetoothAudioAgent "Apple Bitpool Min (editable)" 53

For the HBS-700, 53 is the highest bitpool supported. By default my headset had previously negotiated a much lower bitpool, which corresponds a much lower bitrate. Interestingly, setting the minimum bitpool to 51 actually resulted in worse performance, because of the mismatch of sampling rates between the encoded audio I was listening to (at 48 kHz) and the SBC encoding (at 44.1 kHz). You can examine the negotiated bitrate using this command:

defaults read com.apple.BluetoothAudioAgent

According to the A2DP specs you can get a rough idea of how bitpools correspond to bitrates using the following table:

Table 4.7: Recommended sets of SBC parameters in the SRC device
SBC encoder settings* Middle Quality High Quality
Mono Joint Stereo Mono Joint Stereo
Sampling frequency (kHz)
44.1 48 44.1 48 44.1 48 44.1 48
Bitpool value
19 18 35 33 31 29 53 51
Resulting frame length (bytes)
46 44 83 79 70 66 119 115
Resulting bit rate (kb/s)
127 132 229 237 193 198 328 345
*Other settings: Block length = 16, Allocation method = Loudness, Subbands = 8

Happy listening!

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