Opus decoding to BT (Android)

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student975
Posts: 22
Joined: Tue Nov 27, 2018 9:59 am

Opus decoding to BT (Android)

Post by student975 » Fri Jan 10, 2020 2:00 pm

Hi!

Just want to know is there some explicit downsampling at the case described below.
Opus@200kbps file is played to BT AAC@256kbps. On main window I see for input:

32-bit 48 kHz <variable>kbps OPUS

, and for output:

32-bit 48 kHz STEREO PCM

Hardware shows Bits 64 (out: 32 int), Frequency 48000.
Android "For developers" show 44100 Hz and 16 bit for BT.

So, I see two opportunities:

1. On Opus decoding output rate is set to 44100 (BTW source FLAC was 44100)
2. Somewhere in the chain 48000 to 44100 downsampling takes place

Whin one does take place in reality?

blaubär
Posts: 1313
Joined: Tue Apr 02, 2019 6:48 am

Re: Opus decoding to BT (Android)

Post by blaubär » Fri Jan 10, 2020 2:58 pm

It is rather unlikely that the decoder changes the sampling rate. From the messages you see I would think that everything works with 48 kHz including the delivery to the DAC. What do you mean with "Android For developers" ? The Android Developer Options ?

student975
Posts: 22
Joined: Tue Nov 27, 2018 9:59 am

Re: Opus decoding to BT (Android)

Post by student975 » Fri Jan 10, 2020 4:17 pm

Yes, you are right. It was my literal back translation :)

blaubär
Posts: 1313
Joined: Tue Apr 02, 2019 6:48 am

Re: Opus decoding to BT (Android)

Post by blaubär » Fri Jan 10, 2020 6:11 pm

So everything says 48 kHz ... and the Developer Options do mean what ? I'm not sure what that means, perhaps nothing.

student975
Posts: 22
Joined: Tue Nov 27, 2018 9:59 am

Re: Opus decoding to BT (Android)

Post by student975 » Fri Jan 10, 2020 6:44 pm

I mean these system settings BT-related options.
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blaubär
Posts: 1313
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Re: Opus decoding to BT (Android)

Post by blaubär » Fri Jan 10, 2020 7:26 pm

Okay ... so the preferred sampling rate for BT is 44.1 kHz ... so what do you think that means ? Do you think this implies that this sampling rate is forced rather than preferred ? ... and whatever you think, do you know rather than guess ? I suggest you ask in an android/google/samsung forum, they might know more. Or perhaps the developer here knows something, I don't.

student975
Posts: 22
Joined: Tue Nov 27, 2018 9:59 am

Re: Opus decoding to BT (Android)

Post by student975 » Fri Jan 10, 2020 8:13 pm

blaubär wrote:
Fri Jan 10, 2020 7:26 pm
Do you think this implies that this sampling rate is forced rather than preferred ?
Exactly! The thing is it's the only possible sampling rate in the list. So, I'd prefer NMP to downsample as having more accurate DSP. But output params still shows 48kHz, and I guess it results in using of system DSP to downsample.

The problem is, OPUS hasn't got 44100 sampling frequency.

blaubär
Posts: 1313
Joined: Tue Apr 02, 2019 6:48 am

Re: Opus decoding to BT (Android)

Post by blaubär » Fri Jan 10, 2020 8:37 pm

student975 wrote:
Fri Jan 10, 2020 8:13 pm
blaubär wrote:
Fri Jan 10, 2020 7:26 pm
Do you think this implies that this sampling rate is forced rather than preferred ?
Exactly! The thing is it's the only possible sampling rate in the list. So, I'd prefer NMP to downsample as having more accurate DSP. But output params still shows 48kHz, and I guess it results in using of system DSP to downsample.

The problem is, OPUS hasn't got 44100 sampling frequency.
So you think that because you cannot change the value ( that's what you mean by "only possible sampling rate" ? ) then sampling rate will be changed to 44.1 kHz by the os or the bt device after nmp delivered its output with 48 kHz . That would imply that Neutron doesn't succeed in finding out that only 44.1 kHz is valid. And you want neutron to downsample so that the os or the bt device don't have to.
Okay, as to the immediate action : set the sampling rate in the Audio Hardware Settings to 44.1 kHz.
And as to your suspicion about neutrons inability to correctly checking your device, you might tell us what that device and operating system is.

blaubär
Posts: 1313
Joined: Tue Apr 02, 2019 6:48 am

Re: Opus decoding to BT (Android)

Post by blaubär » Fri Jan 10, 2020 8:45 pm

Another thing you could do : change the bt-codec if it is possible on your devices, e.g. ldac can provide higher sampling rates.

student975
Posts: 22
Joined: Tue Nov 27, 2018 9:59 am

Re: Opus decoding to BT (Android)

Post by student975 » Fri Jan 10, 2020 9:20 pm

blaubär wrote:
Fri Jan 10, 2020 8:37 pm
So you think that because you cannot change the value ( that's what you mean by "only possible sampling rate" ? ) then sampling rate will be changed to 44.1 kHz by the os or the bt device after nmp delivered its output with 48 kHz . That would imply that Neutron doesn't succeed in finding out that only 44.1 kHz is valid. And you want neutron to downsample so that the os or the bt device don't have to.
Yes!
blaubär wrote:
Fri Jan 10, 2020 8:37 pm
Okay, as to the immediate action : set the sampling rate in the Audio Hardware Settings to 44.1 kHz.
Unfortunately, there are 48, 98, 192 and 384 only.
blaubär wrote:
Fri Jan 10, 2020 8:37 pm
And as to your suspicion about neutrons inability to correctly checking your device, you might tell us what that device and operating system is.
It's Huawei MediaPad M6 running Android 9. Intersection of earphones (DALI IO-4) and tablet BT codecs sets results in SBC and AAC only (it's relatively new Huawei device already under licensing limits).

Now I start to guess it is more appropriate to avoid demand from NPM too much and to re-encode files to m4a/aac instead of opus - the last one hasn't got 44100 sample rate by design (48kHz only).

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