On 10.06.2019 17:53, Pali Rohár wrote:
> On Wednesday 05 June 2019 22:42:49 ValdikSS wrote:
>> On 02.06.2019 18:25, Pali Rohár wrote:
>>> Specify configuration for Low, Middle, High and Ultra High Quality of SBC
>>> codec. SBC codec in Ultra High Quality has higher quality than aptX.
>>>
>>> Automatic Quality mode matches configuration of SBC codec which was used
>>> before this change. Which means that it accept configuration between Low
>>> and High quality.
>>>
>>> Current SBC code was extended to allow definitions of arbitrary
>>> configuration variants of SBC codec parameters.
>>> ---
>> ...
>>> +
>>> +/* SBC Ultra High Quality, calculated to minimize wasted bytes and to be
>>> below max possible 512 kbps */
>>> +static const a2dp_sbc_t sbc_uhq1_caps_table[] = {
>>> + FIXED_SBC_CAPS(SBC_CHANNEL_MODE_JOINT_STEREO, SBC_SAMPLING_FREQ_44100,
>>> 76), /* 454.8 kbps */
>>> + FIXED_SBC_CAPS(SBC_CHANNEL_MODE_JOINT_STEREO, SBC_SAMPLING_FREQ_48000,
>>> 76), /* 495 kbps */
>>> + FIXED_SBC_CAPS(SBC_CHANNEL_MODE_STEREO, SBC_SAMPLING_FREQ_44100,
>>> 76), /* 452 kbps */
>>> + FIXED_SBC_CAPS(SBC_CHANNEL_MODE_STEREO, SBC_SAMPLING_FREQ_48000,
>>> 76), /* 492 kbps */
>>> +};
>>> +static const a2dp_sbc_t sbc_uhq2_caps_table[] = {
>>> + FIXED_SBC_CAPS(SBC_CHANNEL_MODE_DUAL_CHANNEL, SBC_SAMPLING_FREQ_44100,
>>> 38), /* 452 kbps */
>>> + FIXED_SBC_CAPS(SBC_CHANNEL_MODE_DUAL_CHANNEL, SBC_SAMPLING_FREQ_48000,
>>> 38), /* 492 kbps */
>>> + FIXED_SBC_CAPS(SBC_CHANNEL_MODE_MONO, SBC_SAMPLING_FREQ_44100,
>>> 37), /* 226 kbps */
>>> + FIXED_SBC_CAPS(SBC_CHANNEL_MODE_MONO, SBC_SAMPLING_FREQ_48000,
>>> 37), /* 246 kbps */
>>> +};
>> ...
>>
>> While working on Android SBC HD patch, allowing bitpools higher than 53
>> unfortunately introduced problems with some headphones. All major OS have
>> maximum bitpool locked to 53, and it seems there's a reason for that:
>> compatibility with broken devices. I had to revert bitpool increasing patch
>> in the final release and implement only Dual Channel patch.
> It is a problem if pulseaudio/bluez exports one SEP with fixed SBC
> bitpool 76 (min = max = 76) and another SEP with dynamic SBC bitpool
> range 2-53?
Probably not a problem, I'm not sure.
>
>> Some notes regarding UHQ profiles:
>> 1. It would be great to use bitpool 38 for Dual Channel 2-DH5 (EDR 2 mbit/s)
>> and bitpool 47 for Dual Channel 3-DH5 (edr 3 mbit/s), automatically
>> detecting link speed. It pushes bitrate even further for 3-DH5 compatible
>> devices (551 kbit/s for 44.1 kHz, 5 audio frames) and makes SBC on par with
>> aptX HD. That's what I did for Android patch.
> How can be detect link speed? Is there some kernel API for it? Or deduce
> it from socket send buffer size?
Android exports EDR speed into media encoder, I don't know of Linux BlueZ stack
much. Can you determine link MTU from inside the PulseAudio? If you can, you
can use that: if MTU is more than 679, than it's most probably 3-DH5 mode (EDR
3mbit/s with 5 slots).
>
>> 2. It's possible to introduce another "extreme quality" profile for 2-DH5
>> (EDR 2 mbit/s) Dual Channel, with 648 kbps @ 48 khz, 595.4 kbps @ 44.1 khz
>> (Up to 3 frames for 2DH5).
>>
>> By the way, SBC HD patch has been merged into LineageOS 15.1 (Android 8) and
>> LineageOS 16.0 (Android 9). If you use LineageOS, you can now enable Dual
>> Channel in Bluetooth device settings (it's called HD Audio: SBC HD).
>>
>> Besides my old SBC HD bitrate calculator
>> (https://btcodecs.valdikss.org.ru/sbc-bitrate-calculator/), I made
>> in-browser realtime SBC and aptX/HD encoder, with frequency spectrum
>> analyzer. You can now easily experiment with Bluetooth codecs quality:
>> https://btcodecs.valdikss.org.ru/sbc-encoder/
>>
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