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Author Topic: Bit perfect or direct audio not possible?  (Read 4715 times)

JBassett

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Bit perfect or direct audio not possible?
« on: September 24, 2016, 03:00:08 am »

I'm running Media Center 22 on Linux Mint into a USB DAC.

I was hoping that JRiver would be able to provide bit perfect audio ro the DAC but it looks as if there is always some sort of processing being done.

The input file is 24 bit 96 kHz flac and I want that decoded 24 bit 96 kHz file to be sent to the DAC without any other "improvements".  However I try to use the options available, the audio path always indicates that there is some processing happening and in particular a 32 bit file is being sent to the DAC.  The DAC is only 24 bit capable and the response seems to be to drop the sample rate down to 48 kHz.

Is there any way to make sure there is absolutely no audio processing being applied (other then decoding the flac file - I even tried a WAV file but with the same result.

Thanks
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JimH

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Re: Bit perfect or direct audio not possible?
« Reply #1 on: September 24, 2016, 07:16:11 am »

Your DAC may be requesting 32 bit data.

What is the DAC?  How is it connected?
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JBassett

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Re: Bit perfect or direct audio not possible?
« Reply #2 on: September 24, 2016, 11:35:49 am »

It's a Devialet 200 being fed via USB.

Other playback software such as GBrowser seem to get the sampling frequency correct and send 96 kHz data to the DAC from a 96 kHz file, 88.2 kHz data from an 88.2 kHz original as I would expect.

I prefer the JRiver interface and would like to get it working.  If it's not going to be possible then I'll just have to stick with what seems to work.
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mwillems

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Re: Bit perfect or direct audio not possible?
« Reply #3 on: September 24, 2016, 11:49:52 am »

What output device setting are you using in MC for Linux (Tools-->Options-->Audio-->Audio Device)?  There's usually a long list of devices there (various alsa devices, pulse, etc.).

I would bet even money that you have the pulse audio or the default alsa output selected as both of those system mixers default to 48KHz on Linux and MC would need to resample to output to them.  Try instead selecting one of the hardware outputs (they have names that start with "front:" or "surround:"  That's what you need to get a direct connection.
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JBassett

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Re: Bit perfect or direct audio not possible?
« Reply #4 on: September 25, 2016, 02:03:58 am »

I was using what I assumed was the output specific to the DAC I was using close to the top of the list "dmix:CARD=D20.DEV=0 [ALSA].  I didn't look any down to the other options.

I have tried the equivalent "front:" device and all now seems to be working as I would like with no changes reported in the audio path.

I haven't tried other options yet but is there any difference or advantage in using one of the other options e.g. hw:

Thanks for you help!
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Hendrik

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Re: Bit perfect or direct audio not possible?
« Reply #5 on: September 25, 2016, 02:12:03 am »

The "dmix" devices are a software mixer from ALSA, they don't give direct hardware access - so that explains this, then! :)
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geier22

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Re: Bit perfect or direct audio not possible?
« Reply #6 on: September 25, 2016, 10:35:08 am »

Did you set the correct values in the DSP Studio- Settings?

 
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mwillems

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Re: Bit perfect or direct audio not possible?
« Reply #7 on: September 25, 2016, 11:15:37 am »

I was using what I assumed was the output specific to the DAC I was using close to the top of the list "dmix:CARD=D20.DEV=0 [ALSA].  I didn't look any down to the other options.

I have tried the equivalent "front:" device and all now seems to be working as I would like with no changes reported in the audio path.

I haven't tried other options yet but is there any difference or advantage in using one of the other options e.g. hw:

Thanks for you help!

Devices starting with "front:" are the stereo output hardware device (as distinct from the surround hardware devices, etc.), so assuming you want a direct 2-channel output "front:" is as direct as it's going to get.  Glad to hear it's sorted, happy listening!
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