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A way to record a USB digital audio signal?

garbulky

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#1
On the Emotiva forums, we've had a discussion regarding the Microrendu. The people that have used it have reported a better sound. The confusion is how can something that measures at best identical sound different especially considering its a digital stream.

Some have mentioned the MR may be changing the digital data somehow.
So is there a way to test just the digital output of the microrendu to compare it to just the USB stream from a laptop?

So basically I would like to know if the digital USB output of the Microrendu is "bit perfect" and identical to the USB output from say a laptop. Ideally I would like to know if the signals arrived at the same timing. But if not, if there was simply a way to figure out if the exact same bits arrived. Is there such a device that can measure this?
 

amirm

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#3
Timing capture will be beyond difficult, requiring a very expensive digital scope. And then you have to analyze what you are seeing (audio samples as opposed to USB protocol).

What @Soniclife suggests will work. Another alternative is to send a dolby digital stream to it to a DAC that has S/PDIF out and feed that to an Audio/Video Receiver to see if it can decode it.

Of you could be nice to me :), send me some cookies for holidays, and I will point you to my review of MicroRendu: https://www.audiosciencereview.com/...ts-of-sonore-microrendu-v1-4.1867/#post-48479
 

Pluto

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#4
I would like to know if the digital USB output of the Microrendu is "bit perfect" and identical to the USB output from say a laptop ....... if there was simply a way to figure out if the exact same bits arrived. Is there such a device that can measure this?
The easiest way is to use a DAC that includes such a test within its feature set. In principle, you put the DAC into its test mode, play a file provided by the manufacturer and within a few seconds you get an answer. There are no DACs, to my knowledge, that provide any kind of more quantitative result than simply OK or not.

Two DACs which include such a test are the Audiolab M-DAC and RME ADI-2 Pro.
 

amirm

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#5
Two DACs which include such a test are the Audiolab M-DAC and RME ADI-2 Pro.
Good suggestions. Berkeley Alpha DAC also has an HDCD decoder when fed with the right bits will light up its indicator.
 

somebodyelse

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#6
The Raspberry Pi Zero (among other similar boards) can be configured to present itself as a class compliant USB audio device, which should allow the audio data sent to be recorded and compared. I've not had cause to actually try it before, and I'm aware the method has changed a bit. Handy keywords 'otg' and 'g_audio'. Assuming it works it would be a cheaper 'test mode' option than those DACs.
 
OP
G

garbulky

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Thread Starter #7
Timing capture will be beyond difficult, requiring a very expensive digital scope. And then you have to analyze what you are seeing (audio samples as opposed to USB protocol).

What @Soniclife suggests will work. Another alternative is to send a dolby digital stream to it to a DAC that has S/PDIF out and feed that to an Audio/Video Receiver to see if it can decode it.

Of you could be nice to me :), send me some cookies for holidays, and I will point you to my review of MicroRendu: https://www.audiosciencereview.com/...ts-of-sonore-microrendu-v1-4.1867/#post-48479
Amir I read your review which is what started my questioning. Clearly there isn't a difference in appropriate power supplies.
So it looks like the timing capture will be too difficult. But is there a way to say capture the digital PCM data sent out of the USB output on the MR and compare it to the digital data that should be present on a wav file? I.e. does it transmit the exact same bits?
 

Blumlein 88

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#8
There are ways to test this. Maybe at this point an appropriate question is what other gear do you have to use for testing? Any AV receivers or preamps? DACs that have digital output of some form? Portable players?

I'd use soniclife's approach. Use an USB to SPDIF converter, feed the SPDIF result to the digital input of one of my recording interfaces which could record it. Compare with and without the rendu and to the original. If you don't have the recording interface or SPDIF converter you'll need another method.
 

amirm

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#9
So it looks like the timing capture will be too difficult. But is there a way to say capture the digital PCM data sent out of the USB output on the MR and compare it to the digital data that should be present on a wav file? I.e. does it transmit the exact same bits?
It transmits identical data.
 

mitchco

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#10
So is there a way to test just the digital output of the microrendu to compare it to just the USB stream from a laptop?

So basically I would like to know if the digital USB output of the Microrendu is "bit perfect" and identical to the USB output from say a laptop. Ideally I would like to know if the signals arrived at the same timing. But if not, if there was simply a way to figure out if the exact same bits arrived. Is there such a device that can measure this?
Yes, there are a couple of approaches and generally requires a multi-client ASIO driver, like the Lynx Hilo I am using. It allows you to run experiments like:

https://www.computeraudiophile.com/...c-vs-JRiver-Windows-Sound-Quality-Comparison/

https://www.computeraudiophile.com/...gital-Audio-–-Bit-Perfect-Audibility-Testing/

https://www.computeraudiophile.com/blogs/entry/161-1644-vs-24192-experiment/

https://www.computeraudiophile.com/blogs/entry/154-jriver-vs-jplay-test-results/

A couple of approaches using an ADC:

https://www.computeraudiophile.com/blogs/entry/153-flac-vs-wav-part-2-final-results/

http://archimago.blogspot.com/2013/05/protocol-diffmaker-audio-composite-dmac.html

Maybe some of that is useful... I hope you have fun! And share your results :)
 
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