file USB Audio Signal Question

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ArthurDaniels Posted 1 year 3 months ago
#22310
It is my understanding that USB Audio is a digital signal in format. The term USB Audio typically refers to the signal in a PC or MAC resulting from playing WAV, FLAC, MP3, or other digital format signals with a software music player resident within the computer. Instead of allowing the computer's DAC to translate the signal to audio, the USB Audio is still a digital signal that is sent directly to the computer's output and is available at any one of the computer's USB ports.

Typically, this USB Audio signal is transported via USB cable to an external DAC for D/A conversion. My question is: Is there a difference between the USB Audio digital signal and a standard PCM digital signal which is present at the output of a CD or DVD player? If so, what is the difference?

Thanks,

Art
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GDHAL Posted 1 year 3 months ago
#22333
Hi Art. I'm definitely no expert in terms of being able to answer your question, however, I believe the operative word in your write up is *typically*. To my understanding, typically the USB data stream will in fact be "PCM", the exact same PCM format as if you were to play from a CD and not use USB. However, USB data transfer can also support other formats besides PCM. This (example) article contains the details (yes, the document is 1998 but note the contributors and URL) www.usb.org/developers/docs/devclass_docs/frmts10.pdf
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ArthurDaniels Posted 1 year 3 months ago
#22335
HI GDHAL,

Thanks for your reply. The article confirms that the most likely format would be PCM and I am confident now that the data stream from my music PC is PCM.

I can send this data stream directly to my Denon AV Receiver and it is properly handled. My transport method is to send the data stream via USB Audio to my external DAC. The DAC has both optical and coaxial digital outputs and will transport the stream without modifications via these outputs.

A curious discovery from my experiments is that, if I send the data stream from the DAC to my Denon via coaxial, the Denon does not recognize the data. But, if I send the data via optical, the Denon happily processes the data.

It appears that my Denon does not recognize the stream as digital when received via a coaxial input. This may be a Denon setup problem, but if so, I have not yet figured out what to change. It does not matter since I can use the optical transport and I don't plan to spend any more time on that issue at present.

Thanks again for your reply.

Best,

Art
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