limit on sampling rate for Bluetooth

Support questions for Neutron Player only (http://neutroncode.com/apps/player).
WitzyZed
Posts: 244
Joined: Fri Nov 22, 2019 8:49 pm

Re: limit on sampling rate for Bluetooth

Post by WitzyZed » Sat Feb 20, 2021 9:13 am

1- mp3 320kbps > neutron(24 bit at 96khz) > OS > downsampling to 16 bit at 44.1 khz (quality 1)
2-flac 1.4Mbps > neutron (24 bit at 96khz) > OS > downsampling to 16 bit at 44.1 khz (quality 2)
Why are you set on including 24bit/96kHz in this hypothetical at all? If the file is 16 bit, 44.1kHz, mp3 or flac, you should just output at 44.1kHz.

Eyes and ears are different tools. Sure it's 1s and 0s in digital domain but megapixel comparisons to audio are a complete misnomer.

blaubär
Posts: 3442
Joined: Tue Apr 02, 2019 6:48 am

Re: limit on sampling rate for Bluetooth

Post by blaubär » Sat Feb 20, 2021 9:50 am

A better fitting analogy could go like this :
  • song with CD quality <-> picture with a low resolution
  • flac <-> raw picture format
  • mp3 <-> lossy compressed picture format like jpg
  • audio decoding from flac or mp3 to pcm <-> retrieval of pixels from raw or jpg format image files
  • upsampling <-> extrapolation of the picture to a higher resolution
  • data processing in Neutron <-> processing of image in some picture editor
  • downsampling <-> extrapolation of the picture to a lower resolution
  • bluetooth <-> lossy picture transformation, transport and retrieval of pixels
  • loudspeakers, headphones <-> printer, monitor
  • ear <-> eye
And the answer probably would depend on the image-compression-algorithm, the extrapolations, the monitor, printer, paper, the picture editor and your eyesight.

tavrouss
Posts: 26
Joined: Sat Feb 13, 2021 7:58 pm

Re: limit on sampling rate for Bluetooth

Post by tavrouss » Sat Feb 20, 2021 5:22 pm

Which of the Bluetooth audio codes(SBC,AAC,APTX,APTX HD,ADAC) causes the quality of the .flac file(16 bit 44.1 khz with 1.4 Mbps bitrate) to decrease?

blaubär
Posts: 3442
Joined: Tue Apr 02, 2019 6:48 am

Re: limit on sampling rate for Bluetooth

Post by blaubär » Sat Feb 20, 2021 6:06 pm

tavrouss wrote:
Sat Feb 20, 2021 5:22 pm
Which of the Bluetooth audio codes(SBC,AAC,APTX,APTX HD,ADAC) causes the quality of the .flac file(16 bit 44.1 khz with 1.4 Mbps bitrate) to decrease?
All of them, see here . Although most people won't here this.

Farshad
Posts: 6
Joined: Fri Feb 12, 2021 9:08 pm

Re: limit on sampling rate for Bluetooth

Post by Farshad » Mon Feb 22, 2021 6:22 pm

I recently enconter that bluetooth connects with 16bit 48khz and can not change to hd bluetooth I need to close application and disconnect bluetooth for many times to let it switch to 24bit 96khz... Why ?

blaubär
Posts: 3442
Joined: Tue Apr 02, 2019 6:48 am

Re: limit on sampling rate for Bluetooth

Post by blaubär » Mon Feb 22, 2021 6:29 pm

Farshad wrote:
Mon Feb 22, 2021 6:22 pm
I recently enconter that bluetooth connects with 16bit 48khz and can not change to hd bluetooth I need to close application and disconnect bluetooth for many times to let it switch to 24bit 96khz... Why ?
That might be a problem of the operating system and the headphones (or whatever you've connected) to agree on a common bluetooth codec. Perhaps you can check the Android Developer Options to see what codec is active in the two cases ?

Farshad
Posts: 6
Joined: Fri Feb 12, 2021 9:08 pm

Re: limit on sampling rate for Bluetooth

Post by Farshad » Mon Feb 22, 2021 7:05 pm

blaubär wrote:
Mon Feb 22, 2021 6:29 pm
Farshad wrote:
Mon Feb 22, 2021 6:22 pm
I recently enconter that bluetooth connects with 16bit 48khz and can not change to hd bluetooth I need to close application and disconnect bluetooth for many times to let it switch to 24bit 96khz... Why ?
That might be a problem of the operating system and the headphones (or whatever you've connected) to agree on a common bluetooth codec. Perhaps you can check the Android Developer Options to see what codec is active in the two cases ?
In developer options it is showing AAC codecs enabled and sampling rate 44.1khz and 16bit . But I am able and was able to get 32bit 192khz with neutron . But after update I am left with 24 bit and 96khz sample rate my device is xiaomi redmi note 9s and bluetooth device is haylou t15 which uses latest bluetooth 5 with realtek 8763VXP chipset . In the list of sampling I can choose between 44.1 to 96khz. But also when I disconnect bluetooth neutron switches to 16bit 44.1khz even with hi-res speaker enabled

Farshad
Posts: 6
Joined: Fri Feb 12, 2021 9:08 pm

Re: limit on sampling rate for Bluetooth

Post by Farshad » Mon Feb 22, 2021 7:21 pm

I found out I have to switch high res speaker off and on to let it enabled and let bluetooth to hi res too.

blaubär
Posts: 3442
Joined: Tue Apr 02, 2019 6:48 am

Re: limit on sampling rate for Bluetooth

Post by blaubär » Mon Feb 22, 2021 7:49 pm

Bluetooth won't support a sampling rate higher than 96 kHz, as has ben said by the developer before :
dmitrykos wrote:
Mon Feb 15, 2021 8:01 am
Farshad wrote:
Fri Feb 12, 2021 9:24 pm
After recent update we are limited to Bt 24 bit 96khz sampling rate . Why ?
I was. Able to get 32bit 192khz sampling over generic driver with haylou t15 and sounded really good why. Are we going backward ? At least leave us an option to unlimit with our risk of anything ?
Bluetooth A2DP does not support anything higher than 24/96 format (https://en.wikipedia.org/wiki/List_of_codecs#Bluetooth), therefore this limit prevents users to misuse the format that will cause double re-sampling: Neutron upsamples -> OS downsamples to some supported frequency.

blaubär is correct with comment how it works: Neutron provides possibility to the OS to use hi-res format and send it as is. For example if OS supports LDAC (it became a part of AOSP Android source by the way by the decision of Sony) then it can transfer 24-bit with 44100 - 96000 frequencies to your LDAC headphones.

There is no guarantee though that it will happen for sure because Android's audio API is limited in this sense and there is no reliable feedback from it, so you need to re-check the result using indication of headphones or BT DAC (for example Qudelix 5K has companion app which shows the format in which device is receiving the signal).
If you somehow confound Neutron so that is uses more than 96 kHz the operating system will downsample.

blaubär
Posts: 3442
Joined: Tue Apr 02, 2019 6:48 am

Re: limit on sampling rate for Bluetooth

Post by blaubär » Sun Feb 28, 2021 9:06 am

In the next version there will come another minor change : Neutron will use 32-bit-floating-point for output to Bluetooth to avoid compatibility issues with the Bluetooth Adapters .
Neutron calculates with 32 or 64 bit integer and then transforms to floating point because that gives less trouble with the bt adapters ?
Yes exactly, because Android allows to use either 16-bit Integer format or 32-bit Floating, there is no 24-bit Integer when using the public Android audio API when working directly with device entity (like BT A2DP). Using 24-bit Integer resulted in a silence bug for some users, so 32-bit Floating is the safest and also hi-res format which allows 24-bit data for BT A2DP.
what about dithering ? If Neutron transforms to 32 fp then itnees not dither ... but if the bt adapter only takes 16 bit it had better done ?
BT protocol will do lossy encoding for the transmission, so dithering will not play any role here as lossy conversion will modify data anyway. So for this given case it makes no sense.
Also see What is 32 bit floating?
So… 32 bit floating is a 24 bit recording with 8 extra bits for volume.

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