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External USB sound card, digital out

post #1 of 27
7/1/04 at 11:52pm
Thread Starter 
I have a Yamaha DP-U50 external USB soundcard. There is an optical out. So when I use the optical out on the soundcard, does the data from the computer go through the Yamaha's DAC? Or is it bypassed?
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post #2 of 27
7/2/04 at 12:00am
should be bypassed
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post #3 of 27
7/2/04 at 12:54pm
Thread Starter 
Thanks.

Then if you use the digital out on the soundcard, and use an external DAC, is there a difference in sound quality amongst the different external usb soundcards?
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post #4 of 27
7/2/04 at 1:08pm
Yes. Some USB sound devices (e.g. Xitel) can only output signals at 48kHz, so the digital signal gets resampled before being output. There are other USB devices that can output a 44.1kHz signal but don't do it perfectly.
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post #5 of 27
7/2/04 at 1:15pm
Thread Starter 
The Grace 901 has a indicators indicating the input sampling rate. I was using foobar last night, looks like the Grace was getting 44.1khz input.

Any ideas on how good the Yamaha DP-U50 digital output is?
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post #6 of 27
7/2/04 at 1:46pm
That's very good to know. I don't have any more information about the U50's digital out. Do you have a home theatre receiver? If so, you can test the device to see if it's bit-perfect.
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post #7 of 27
7/2/04 at 2:13pm
Thread Starter 
No, I don't have a home theater receiver.

All I have are Benchmark DAC1, and the Grace 901.

How would you test to see if the optical output from the Yamaha soundcard is bit perfect?
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post #8 of 27
7/2/04 at 2:31pm
The easiest way is to download a 44.1kHz PCM encoded DTS/Dolby Digital test file and try playing it back through a digital link to a home theatre receiver that can decode DTS/Dolby Digital. If all the bits come through unchanged, the receiver will be able to decode it, and you'll hear music. Otherwise, you'll hear loud static. If you're concerned about the quality of your digital output, it's worth borrowing a friend's HT receiver for an evening just to try this out. If you do, please report back your findings to the forum, so we'll be able to help out others.

The other way to check for bit-perfectness is to connect the card's digital out to a sound card with a digital in, and record the output and compare it on a bit-by-bit basis with the source material, after adjusting for the initial offset. There is one guy on HydrogenAudio who does this.
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post #9 of 27
7/2/04 at 2:33pm
Thread Starter 
Thanks, I'll try to find someone that'll loan me his HT receiver

Where can you find those test files?
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post #10 of 27
7/2/04 at 2:34pm
Thread Starter 
Which reminds me, the Yamaha usb sound card has both digital in and digital out. Does that mean I can make a loop, connect a toslink cable from the digital out to the digital out, feed back to itself?

The Yamaha card supposedly can decode dolby digital and down mix to dolby surround but not DTS.
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post #11 of 27
7/2/04 at 2:47pm
Here are some links for test files (they might not all still work):
http://www.5dot1.com/articles/ac-3_5...to_a_cd-r.html
http://www.modernrecording.com/artic...6kbps_3min.ZIP
http://www.sr.se/multikanal/english/e_index.stm

Yes, if there is a digital in you can connect the output to the input (it in a loop) and then play something and record it. You'll probably have to use a hex editor to compare the resultant files (unless someone else has a good piece of software to recommend for this).
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post #12 of 27
7/2/04 at 2:57pm
Thread Starter 
Just tried it, it looks like the digital in and out cannot function at the same time, so the loop doesn't work. Have to borrow someone's HT receiver.
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post #13 of 27
7/3/04 at 2:12pm
Let us know when you've had a chance to do the test, ampgalore. I'm curious, since the digital out *does* appear to be at the mercy of the volume control knob, suggesting it might not be bit-perfect.
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post #14 of 27
7/3/04 at 2:20pm
Thread Starter 
The volume control knob does not affect the digital out. It only affects the analog out on the back.
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post #15 of 27
7/4/04 at 1:07am
Yep, you're right, my bad.
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