Bluetooth Headphones and all things codecs

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Ok, you knew life wouldn’t be simple, but now that Apple (and Google and everyone else) are eliminating that 3.5mm jack, it does seem like a push to Bluetooth wireless headphones is inevitable. Naturally, technology means that it is super complicated to get audiophile quality from these things. Here’s a short decoder ring:

Format available

There is a sea of codecs available with very different specifications.

  1. The default codec that works with all Bluetooth is called SBC and has mediocre quality. This is a lossy format, so most people play MP3 through SBC and it sounds pretty OK mainly because the original source material isn’t that great. Max rate is 320Kbps at 48KHz. It is also quite laggy, so sometimes, you get a lag between the time that someone speaks and you hear it on your headphones in a movie. It uses LPCM which is an older style of codec.
  2. Next up is AAC which is Apple’s proprietary codec which uses wavelet compression and is more advanced and is 250Kbps.
  3. Then QUALCOMM AptX at 320Kbps and then AptX HD at 520Kbps. This uses adaptive differential PCM, so it is supposed to be near CD quality.
  4. Finally Sony LDAC has a very high resolution lossless format at 1Mbps in high priority with two other modes at 330Kbps and 660Kbps

Source Devices

Both the headphone and the bluetooth transmitter have to support more advanced codecs. So starting with the typical devices:

  1. With Apple, there are really only two choices. With iPhones, they SBC and then their own AAC format, but not all headphones support ACC.
  2. With the Mac, you get SBC, AAC and also Qualcomm’s AptX, but it isn’t easy to figure out what you are using, you need to hold down the Option key and click on the Bluetooth icon and then you can see what Codec is being used. Most of the time, the negotiation is automatic, but if it doesn’t work, then you have to download the Bluetooth Explorer and force it.
  3. For Android, you get way more choices, there is the AptX, but for Android Oreo (the latest release), you get yet another choice, the high resolution Sony format.

Headphones

Well, before you buy a set of headphones, it’s good to figure out what they support as an example:

  1. V-Moda Crossfade. They are typical lower cost but higher quality. The original Crossfade only supported SBC. The new Crossfade 2 is more complicated. The regular Crossfade only supports SBC and AptX, but the Codex edition supports SBC, AptX and AAC.
  2. Sony WH-1000XM3. This is their third model and they support everything including AAC the apple format. For a $350 headphone, it had better. The older WH-1000XM2 is the same way.
  3. Apple AirPods, while the headphones are themselves pretty low fidelity, since it is an Apple product it supports SBC (this is actually required) and AAC.

Source Material and can you hear the difference?

  1. Now if you are using source material which is an MP3 or a compressed format, then it is not clear how much difference this makes, so for the best quality, you want to rip your own CDs (if you still have those) and encode them as FLAC (a loss less format). Even this only gives you 16-bit audio.
  2. So the very best thing to do is to subscribe to Tidal which sends things down in 24-bit at 96KHz.
  3. Finally if you are streaming then non of this really matters, most streaming is done at 128Kbps, so this doesn’t matter much.

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