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sampling frequency confusion
#1
Hi,
I'm on latest moode, my source is on a NAS wav files with 32 bit pre-convolved with ConvoFS.

If I resample everything in ConvoFS to eg. 176400Hz, I'm getting under audio information:
encoded at: 32bit 176,4kHz Stereo PCM
decoded to: 32bit 176,4kHz Stereo
Output rate: 32bit 176,4kHz Stereo

So everything fine.

When then resampling with SOX on the Pi 3B+ 64bit kernel to 352,8kHz I get Output rate: 32bit 192kHz Stereo.
Why?


Other game:
If I resample everything in ConvoFS to eg. 352800Hz, I'm getting under audio information:
encoded at: 32bit 352,8kHz Stereo PCM
decoded to: 32bit 352,8kHz Stereo
Output rate: 32bit 192kHz Stereo
Why?

My goal is to set everything in ConvoFS to 32bit wav, 352,8kHz and my moode rpi is doning nothing expect playback.
This is because my DAC is internally upsampling everything to 8x samplingfrequency - but with SOX it sounds better then with the upsampling from the DAC.

A worse but also possible solution would be to set ConvoFS to 176,4kHz and let the moode RPI SOX do the step to 354,8kHz.

But none of the 2 possibilities is working at the moment from the audio information tab info.

Audio device is generic-1, I use an allo isolator, allo Kali reclocker, 3 more Hardware reclocker and then with I2S direct into my AK4497 DAC chip.
It does not change anything when switched to 24 bit wav or flac files, also 32 bit kernel no change.

Hope you can help.

Thanks,
Erich
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#2
"generic-1"  driver works with the HiFiBerry DAC and clones which only handle up to 192kHz

See the moode list of audio devices here...
http://moodeaudio.org/

What does generic-2 or RPI-DAC do ?
----------
bob
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#3
Right, 192K is the max for the generic I2S drivers and also the Allo Isolator limits the rate to 192K. Anything over 192K will sound like white noise.

Regarding AK4497, according to the data sheet there is no way to bypass the oversampling stage.
Enjoy the Music!
moodeaudio.org | Mastodon Feed | GitHub
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#4
Hi,

from the manual of the allo isolator:
"Sampling Frequency ranges from 8 kHz to 384 kHz"

Is there an I2S driver which supports 352,8/384kHz without any chip communication necessary?
A "bare metal" I2S out?

The generic-2 has only 24bits output, I want to use 32bit full chain, because I need the digital volume control.
It sounds dull if you lower volume a lot in 24bit compared to the 32bit chain (I have an full active high end audio system, here I can hear this differences easily).

RPI-DAC I have not tested, thought this is some kind of internal analog audio out, will test it next time I switch the system on.
The descriptions of the different drivers is ...

Yes, no way to disable the oversampling stage, but if you feed in the 8x sampling frequency there is nothing to do for this stage.

BR and happy new year,
Erich
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#5
192K only for Allo Isolator board
https://www.allo.com/sparky/isolator-1-2.html

No such I2S driver in stock Linux kernel. Maybe there is some sort of hacked Linux kernel where someone has compiled the hifiberry and rpi dac drivers with patches that enable higher rates.

Since there is no option to bypass the oversampling stage in the chip it will re-oversample the already externally oversampled input.
Enjoy the Music!
moodeaudio.org | Mastodon Feed | GitHub
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#6
Hi,
I have this isolator:
https://www.allo.com/sparky/isolator.html

Which driver can play 352/384 over I2S?

What should be re-oversample?
If the right data format comes in it should do nothing with the data, only take the current data and put it 1:1 in the output buffer.

BR
Erich
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#7
I2S drivers for the PCM5xxx chips and certain ESS Sabre chips support PCM rates > 192K for example the Allo driver for PCM5122 based Boss DAC or the driver for the ESS Sabre based Katana DAC.

Regarding the oversampling filter in AK4497 and whether it can be disabled you might want to browse or post to the thread at diyAudio https://www.diyaudio.com/forums/digital-...ost5737184

-Tim
Enjoy the Music!
moodeaudio.org | Mastodon Feed | GitHub
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#8
Hello Tim,

thanks for the link, but I know this link - no more information on the internet fount to this topic :-(
Documentation from AKM to this topic is really bad.

But audiophonics ESS9028/... driver is working with 352/384kHz!!!
Thanks for your help!

BR
Erich
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#9
Nice :-)
Enjoy the Music!
moodeaudio.org | Mastodon Feed | GitHub
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