I got the AUNE X1 last year as a "portable" headphone amp / DAC. I did an AB test using this with a friend's Weiss DAC202 (massive price differential) and it sounded pretty good in comparison :-).
14334 The USB implementation is the bog standard BB PCM2707 (adaptive isochronous, only up to 16/48 sampling rate USB 1). The internal DAC is the BB PCM1793. Supposedly, these non-asynchronous USB DAC's are prone to jitter so I wanted to see what happens with the USB hub + external HD file copy condition: 14339 So using the 7-port USB hub, I plugged in the E-MU 0404, the AUNE X1, and the USB hard drive (LaCie, about 3 years old). On the left is the quiet USB hub - no activity other than the test being run - audio played with the AUNE X1 --> 0404 for measuring. Not bad; pretty ideal 16-bit numbers. In the middle column - I started a massive file copy from the USB HD --> internal HD while recording the test (avg transfer rate ~25MB/sec). No difference. On the right, I tortured the hard drive with a file copy to itself - ie. both read and write to the same USB HD (avg transfer rate ~12MB/sec). Notice there IS a rise in the noise floor by 3 dB. Frequency response: 14340 Flat. No difference. Noise level: 14341 As you can see, in the USB HD "self copy" condition, there is an increase in the noise floor. Notice that the noise hits the lower frequencies primarily. THD: 14342 Finally for the THD measures, again, the deviation is primarily in the lower frequencies although there are some distortions around the 1kHz signal as well. Conclusion: Not exactly sure what to make of this really, but I'll give a suggestion. I guess the bottom line is not to have excessive data transfer through the USB bus when listening with a USB DAC (no kidding...). Having said this, I think what I'm seeing here is noise from the external USB HD polluting the DAC rather than any kind of jitter explanation. I suspect that when the HD is used for writing, the electrical noise level goes up and that's all I'm seeing. This would explain the noise floor increasing in the lower frequencies. So, perhaps the better conclusion is to make sure noisy peripherals are not plugged into the USB system when you're listening to the DAC. In case you're wondering, I did this test 3 times in each condition and the rise in noise with the HD 'self copy' case was consistent. Hmmm, if I can find some time tonight, will give the Touch TT3 software mod a try :-). I just don't want to brick my precious Touch! +-------------------------------------------------------------------+ |Filename: AUNE_X1_THD.jpg | |Download: http://forums.slimdevices.com/attachment.php?attachmentid=14342| +-------------------------------------------------------------------+ ------------------------------------------------------------------------ Archimago's Profile: http://forums.slimdevices.com/member.php?userid=2207 View this thread: http://forums.slimdevices.com/showthread.php?t=97950 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
