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#368405 - 24/02/2017 00:45 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30578
Loc: Seattle, WA
Bingo. After installing v3a11, both the 44.1k and 48k tracks sound just fine.

So the issue is that the player software 2.0 isn't very good at resampling the 48 down to 44.1, but 3.0 Alpha is great at it.

Mystery solved!
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Tony Fabris

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#368408 - 24/02/2017 22:05 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13498
Loc: Canada
Whew! Well done, Tony!

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#368409 - 24/02/2017 23:26 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30578
Loc: Seattle, WA
Thanks for all your help!

I still have remaining questions for the empeg guys if they ever see this:
- Is it true that the issue is that the Empeg's DAC is a CD-player DAC which can only accept 44.1khz properly, and that the player software has to do a sample-rate conversion to get it to play on that DAC?
- Does anyone know of any other hardware-based MP3 players that will have the same problem?
- Can anyone think of other situations where a 48khz MP3 file will play back poorly on other kinds of equipment?

By the way, the mixing session that brought all of this up in the first place, was for this video:
https://www.youtube.com/watch?v=_f1doSfY2pQ
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Tony Fabris

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#368412 - 25/02/2017 13:35 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13498
Loc: Canada
I suspect that the new audio engine in v3 (the whole point of v3) is responsible for the improvement.

The Bur-Brown DACs and the DSP chip all claim to handle 48KHz inputs/outputs, and the input to it all comes from the processor chip (software).

EDIT: Ah.. found it. empeg_audio3.c appears to do the actual audio-data output, and it seems to be fixed rate at 44.1 from the processor here. So any artifacts you were hearing must be from the empeg player software conversion to 44.1 before handing off to hardware. v3 appears to do it better.

Cheers

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#368413 - 25/02/2017 13:42 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: tfabris]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13498
Loc: Canada
It seems to be a purely software limit on the Mk2/Mk2a players at least. Perhaps the mk1 had a hardware limit that went away in later versions of the device.

So in theory, the player looks like it could output 48KHz without the software down conversion that currently happens. But the player code (closed source) would need to be modified for that, along with the kernel audio output code in empeg_audio3.c

Unless perhaps there's a bit rate/format limit within the SA1100 processor itself, on the pins used to actually send the digital audio out (?).

Cheers


Edited by mlord (25/02/2017 13:44)

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#368414 - 25/02/2017 16:23 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: tfabris]
peter
carpal tunnel

Registered: 13/07/2000
Posts: 4140
Loc: Cambridge, England
Changing the DAC frequency from track to track is a bit of a non-starter, because then you can't do things like cross-fade. So you have to pick one and stick with it -- and the overwhelming majority of MP3s are 44.1KHz. All sample rates other than 44.1KHz are resampled in software in all car-player versions. (I have a funny feeling that one of the Rio portables really did have a hardware-fixed DAC frequency, and actually resampled everything to 48KHz, but that might have been one of the ones that was never released.)

Peter

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#368415 - 25/02/2017 16:39 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: peter]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 13498
Loc: Canada
Originally Posted By: peter
.. you have to pick one and stick with it ..

Makes sense. Does it also make sense to you that v3 does this much better than v2 player software?


Edited by mlord (25/02/2017 16:40)

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#368417 - 26/02/2017 06:24 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: peter]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30578
Loc: Seattle, WA
Originally Posted By: peter
Changing the DAC frequency from track to track is a bit of a non-starter, because then you can't do things like cross-fade. So you have to pick one and stick with it -- and the overwhelming majority of MP3s are 44.1KHz. All sample rates other than 44.1KHz are resampled in software in all car-player versions.


Of course!!! That makes such total sense!
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Tony Fabris

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#368419 - 26/02/2017 19:00 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: mlord]
Roger
carpal tunnel

Registered: 18/01/2000
Posts: 5528
Loc: London, UK
Originally Posted By: mlord
Does it also make sense to you that v3 does this much better than v2 player software?


The audio path was completely re-written in v3, so ... maybe.
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-- roger

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#368423 - 26/02/2017 22:09 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: tfabris]
tfabris
carpal tunnel

Registered: 20/12/1999
Posts: 30578
Loc: Seattle, WA
Thanks so much for the details, Roger. smile

My friend at Apple has submitted an "enhancement request" for Logic Audio to allow the samplerate of exported MP3s to be selectable instead of hard-coded to the project default sample rate. smile
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Tony Fabris

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#368430 - 28/02/2017 00:34 Re: Empeg and Rio guys: question about 48khz sample rates on Empeg etc [Re: tfabris]
jmwking
addict

Registered: 27/02/2003
Posts: 649
Loc: Washington, DC metro
Another thread showing why I still feel compelled to hang out here!

Thanks for the edumacation...

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