Author Topic: Audio over Bluetooth  (Read 143 times)

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Offline YU7C

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Audio over Bluetooth
« on: August 02, 2019, 05:42:01 am »
Hi,

I need to transfer full audio signal (16bit 20Hz - 20kHz) from Microphone to Windows PC application over Bluetooth, and have selected Microchip BM62 Wireless module.
At the  begining everthing goes flawless: BM62 paired with BT adapter, connected and got BT microphone in Sound.
I got several BT services: Audio Sink, Handsfree Telephony, Headset,...

But audio BW is imited to about 4kHz which told me that only HFP/HSP works, not A2DP.
If I select only A2DP on BM62, then Audio Sink service is only avaliabled but  there is no sound from micropne.

I have connected elecret capsule on the microphone input of BM62.
Perhaps I need line input on BM62 for A2DP audio quality signal?

Does anyone has experinces with BM62?

Thanks,
Vojislav
 

Offline blueskull

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Re: Audio over Bluetooth
« Reply #1 on: August 02, 2019, 05:50:19 am »
A2DP doesn't work with microphone inputs. A2DP is for high quality playback only.
 
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Offline YU7C

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Re: Audio over Bluetooth
« Reply #2 on: August 02, 2019, 02:51:41 pm »
A2DP doesn't work with microphone inputs. A2DP is for high quality playback only.

Can I use a line input for audio streaming and A2DP profile?

Thanks,

Vojislav
 

Offline blueskull

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Re: Audio over Bluetooth
« Reply #3 on: August 02, 2019, 03:14:20 pm »
Can I use a line input for audio streaming and A2DP profile?

It's not about mic or line in, it's about bandwidth.

Standard A2DP consumes 352kbps per data stream, and in the old days, Bluetooth can't support more bandwidth than 1 stream, thus A2DP standard allows only one stereo stream at a time.

To enforce this, each A2DP device must choose from one role, be it a source or a sink, but not both. Thus A2DP can only be unidirectional. Theoretically A2DP can be used for mic or line in, but then you lose playback capability.

To allow playback and record at the same time, other profiles, such as SFP and HPS exist, but those use lower quality codec and thus occupies lower bandwidth.

A device can implement multiple profiles to allow A2DP and HFP/SFP coexistence, to allow a headset/handset to take phone calls, and when not taking a phone call, play high quality music.

But only one profile can be active at a time, so HFP/SFP recording while A2DP playback concurrently is not possible.
 

Offline YU7C

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Re: Audio over Bluetooth
« Reply #4 on: August 02, 2019, 03:51:43 pm »
Ok, but anyway I need only one way path, from the device to PC. If it is not possible have to looking for other solution.

Thanks,
Vojislav
 

Online Jeroen3

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Re: Audio over Bluetooth
« Reply #5 on: August 02, 2019, 04:06:16 pm »
Not only that. A2DP is also compressed, and receiving a2dp is not possible on Windows.
 


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