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Topic: Bluetooth A2DP question and Apple W1 chip. (Read 1963 times) previous topic - next topic
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Bluetooth A2DP question and Apple W1 chip.

I have had this question about A2DP audio that no one seems to be able to answer.

Apple's W1 chip is able to use AAC compression for A2DP streaming to bluetooth headphones and speakers.  Since Apple sells music in AAC format, this seems like an ideal way to avoid the "double compression" problem, where a lossy compressed file such as an MP3, is recompressd using SBC.

But, having combed through various sources on the Internet, and reading the white papers at bluetooth.com, I can't get a good answer to my question.

If I have an AAC file, and both sides of an A2DP connection can handle AAC and do the proper handshake for it, will the file be passed untouched to the speaker/headphones, or will the file first be converted to some uncompressed PCM audio format and then compressed again using AAC?
 

Re: Bluetooth A2DP question and Apple W1 chip.

Reply #1 –
Sender and sink can agree on using a certain codec like SBC, AAC, APT-X, etc.
How they do this and what priority is used, is a bit unclear to me.

What we do is using a media player and choosing an audio device e.g. USB DAC, Bluetooth, etc.
We can apply some DSP like EQ or volume control.
As far as I know this always means the file is decoded to PCM, then the DSP is applied and send to the audio device.
I doubt is one can apply DSP directly on any compressed format like AAC, MP3, FLAC, etc.
Even if possible this would require all DSP to be implemented differently for each supported Codec.
A scenario I do think highly unlikely when using a PC.

The only scenario I can conjecture up to avoid the double compression would be that the media player knows that the file format is AAC (trivial) and the Bluetooth is using AAC as well and send the AAC file directly to the Bluetooth radio without touching is.
Of course in a specific environment this is possible.
Here we use Bluetooth as a streaming protocol.
De sender simply sends the file as is to the streamer and the sink does the decoding and the needed DSP like volume control.

In general the answer to your question will be no.
You have to dive in to the specs of the specific product to find out how it implements this.
As Apple in general talks lifestyle instead of specs you will probably having a hard time to find out.

TheWellTemperedComputer.com