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TOPIC: AC3 input pass-thru for the UDIO-8

AC3 input pass-thru for the UDIO-8 7 months 4 weeks ago #41760

  • minifred
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Can any the input ports of the UDIO-8 pass-thru AC3?
I have the SPDIF version. Up to now I have only succeeded in inputting PCM.

If not, any chance of this being an option in the future?
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AC3 input pass-thru for the UDIO-8 7 months 1 week ago #42068

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@minifred

Unfortunately I'm afraid that it won't support AC3.. :-( Only PCM feeds are supported with the UDIO8.

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AC3 input pass-thru for the UDIO-8 6 months 1 week ago #42446

  • laavu
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I would be interested in ac-3 passthrough as well, since I just purchased a UDIO-8. Can you tell if this is a limitation by the HW or SW/firmware?
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AC3 input pass-thru for the UDIO-8 2 months 4 weeks ago #43951

  • Alikris
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The UDIO-8 has AC3 and DTS passthough, that's why I bought it. Decoding is done by my Meridian Digital Pre-amp (you just need to have the ch1+2 SP/DIF plugged in as ac3 and DTS are passed over two channels. Obviously though the decoder must be able to output multiple channels.)

Here's my test findings which i posted to the Meridian User group:

https://www.meridianunplugged.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=275521&page=2

A photo of my Meridian Display clearly showing it decoding an AC3 stream



(3 front channels / 2 rear and the .1 is the sub output)

The same display but decoding a DTS track:





The DTS or AC3 stream will only be correctly sensed and decoded by the external decoder / pre-amp / multichannel DAC if the computer doesn't alter the stream - even changing the volume slightly on the PC will stop the decoding on the external decoder and you'll just get noise. So you have to make sure all audio "enhancements", tone controls, equaliser etc and volume is bypassed and the USB audio device output is set to exclusive.

Obviously this will only work if your decoder will accept DTS and AC3 streams via its digital inputs. The UDIO-8 is also transparent to B format and Ambisonic UHJ encoded audio. Probably also a few more encoded formats as well. In other words, the UDIO-8 successfully passes through an audio stream without changing it in any way, it is fully transparent.

If you play a DTS or AC3 encoded music track and are only getting a white noise sound then either your decoder is incapable of decoding a DTS or AC3 stream or the stream is being altered somewhere on your computer or decoder before the decoding stage.

It would help to know how you've setup the UDIO-8, what decoder you've plugged it into and what you are using to play the stream on your computer, for example, it took me absolutly ages to figure out how to get VLC player to output the AC3 audio stream from a movie without messing it up and just getting noise.

Ali.

Note to MiniDSP: If you wish to confirm the AC3 and DTS passthrough ability of the UDIO-8 from someone far more authoritative than myself, please contact Kal Rubinson, Senior Contributing Editor, Stereophile.

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Last Edit: 2 months 4 weeks ago by Alikris.
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AC3 input pass-thru for the UDIO-8 2 months 4 weeks ago #43953

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Alikris, this is really an interesting finding. Any idea if it works the other way round? I mean would it be possible to use a UDIO-8 input to feed AC-3 (or DTS) bitstream into HTPC and decode that into individual PCM streams (and then output them from UDIO-8 outputs)? For example, using JRiver in the PC.
Last Edit: 2 months 4 weeks ago by laavu.
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AC3 input pass-thru for the UDIO-8 2 months 4 weeks ago #43970

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laavu wrote:
Alikris, this is really an interesting finding. Any idea if it works the other way round? I mean would it be possible to use a UDIO-8 input to feed AC-3 (or DTS) bitstream into HTPC and decode that into individual PCM streams (and then output them from UDIO-8 outputs)? For example, using JRiver in the PC.
UDIO-8 data sheets says it contains SRC4382 sample rate converter(s) and in the SRC4382 data sheet it says it has automatic detection of non-PCM audio streams (DTS CD/LD or IEC61937 format) and corresponding readable status registers (Register 12: Non-PCM Audio Detection Status Register + PC and PD preamble registers). This sounds promising.
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AC3 input pass-thru for the UDIO-8 2 months 4 weeks ago #43972

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Using audio exclusive mode in the windows sound settings disables the sample rate converter for all streams. In other words it'll pass through whatever the source sample rate (and bit rate) is irrespective of the settings in the UDIO control window.

I think the problem most people have with AC3 and DTS passthrough is that for it to work the audio stream has to be bit perfect which may not be easy or even possible to achieve with some software.

I don't see any reason why the passthrough wouldn't work in the other direction. It'll be interesting to see what results you get.

One issue I've come across is that the inputs and outputs can't be split between different software, certainly not in exclusive mode. (on my computer non exclusive mode isn't bit perfect sadly). What I would want is two MiniDSP ASIO drivers, one input and one output, instead of just the one driver as at present. That way, the input and output could be split and be separately controllable and assignable. I've tried using Virtual Audio Cable to route inputs to a different software device but not had much success so far.

Ali.
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AC3 input pass-thru for the UDIO-8 2 months 2 weeks ago #44190

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@ Alikris

Brillant investigating work! Good job!
We indeed don't mention it as we'd easily open a can of worm of compatibility when it comes to other 3rd party issues (i.e. non miniDSP related) that could prevent the correct AC3/DTS passthrough... That's pretty much the main reason... Once it's on a datasheet/manual, we really assume that we've tested the heck out of it.. If there are variables out of our control that could affect that behavior, we prefer to be safe than sorry..

We appreciate your effort in showing how to put it together. Great work once again!

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