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> In the common case for Apple users (listening to iTunes), the AirPods will have the same quality as wired headphones, since they play back with the same codec

by 394549 8y ago

> In the common case for Apple users (listening to iTunes), the AirPods will have the same quality as wired headphones, since they play back with the same codec/bitrate either way (256kbps AAC). Are they literally piping the AAC-encoded bitstream as it appears in the iTune files straight to the AirPods with no manipulation? Because if they're decoding then re-encoding (e.g. decoding the file to raw to pass to the OS, then re-encoding to sent to the AirPods), there will be quality loss even if both codecs are exactly the same, since you'll have generation loss.

rusk 8y ago
> they're decoding then re-encoding That’s what’s happening. It’s not like Bluetooth uses the AAC codec, it must be decoded and reencoded. I’ve done a direct comparison and the deifference is clearly audible.
- empthought 8y ago
  This is inaccurate when applied to AirPods or other good Bluetooth audio products manufactured in the last couple years. It is accurate for products that only support SBC, though. Bluetooth A2DP supports AAC and AirPods support AAC. Apple would never have released them if this were not the case, because they would sound awful.
empthought 8y ago
Yes, they are literally piping the AAC-encoded bitstream as it appears in the iTunes files with no manipulation. Why would they decode it only to re-encode it?
- 394549 8y ago
  > Why would they decode it only to re-encode it? Because it's more generic and easier to implement. I would imagine to support streaming AAC from the file to the AirPods, they'd need to create a special channel for it in the OS's sound system. Even with that, I don't think it'd work in all cases. Sometimes you have to manipulate the audio. What happens when you need to mix in audio from an app, like an alert sound? The AirPods can't keep using the file's unmodified AAC stream, so you'd have to temporarily stop streaming that to them, decode it, mix in the app audio, re-encode that, and ship the modified stream to the AirPods. All the while you have to keep the timing prefect throughout all the changes or it will be even worse-sounding due to the skips. It's a lot easier to just decode-mix-reencode all the time, since that's a pretty straightforward pipeline, instead of having to switch back and forth between different audio streaming methods, and deal with loads of extra complexity.
  - philjohn 8y ago
    That's exactly what they do - when a call comes in it switches to bluetooth voice codec and it all gets mixed. You notice the reduction in quality, but sync remains rock solid.

by 394549 8y ago

rusk 8y ago

> they're decoding then re-encoding That’s what’s happening. It’s not like Bluetooth uses the AAC codec, it must be decoded and reencoded. I’ve done a direct comparison and the deifference is clearly audible.

empthought 8y ago
This is inaccurate when applied to AirPods or other good Bluetooth audio products manufactured in the last couple years. It is accurate for products that only support SBC, though. Bluetooth A2DP supports AAC and AirPods support AAC. Apple would never have released them if this were not the case, because they would sound awful.

empthought 8y ago

Yes, they are literally piping the AAC-encoded bitstream as it appears in the iTunes files with no manipulation. Why would they decode it only to re-encode it?

394549 8y ago
> Why would they decode it only to re-encode it? Because it's more generic and easier to implement. I would imagine to support streaming AAC from the file to the AirPods, they'd need to create a special channel for it in the OS's sound system. Even with that, I don't think it'd work in all cases. Sometimes you have to manipulate the audio. What happens when you need to mix in audio from an app, like an alert sound? The AirPods can't keep using the file's unmodified AAC stream, so you'd have to temporarily stop streaming that to them, decode it, mix in the app audio, re-encode that, and ship the modified stream to the AirPods. All the while you have to keep the timing prefect throughout all the changes or it will be even worse-sounding due to the skips. It's a lot easier to just decode-mix-reencode all the time, since that's a pretty straightforward pipeline, instead of having to switch back and forth between different audio streaming methods, and deal with loads of extra complexity.
- philjohn 8y ago
  That's exactly what they do - when a call comes in it switches to bluetooth voice codec and it all gets mixed. You notice the reduction in quality, but sync remains rock solid.