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I downloaded an album from Hdtracks yesterday and had a listen...full 24/192. Two of the tracks give a huge amount of hissing when using the HDVD800. When I've loaded them all on my AK120 they're fine. It sounds like a deluge of rain in the background to the track. Confused as to why it's only doing it on 2 tracks out of 10...
That is exactly the issue that I've been trying to track down. The problem does seem to be in the DAC itself. Here is what seems to trigger the issue:
1) Full 24/192 tracks. If you pull away from that sample rate or down sample, the problem goes away. Also, the issue doesn't show up on all 24/192 tracks but the tracks it does show up on, will consistently repeat the problem (which is strange that the content of some tracks will trigger the issue and others won't. In fact, some tracks that I have, the hiss actually ramps up at the beginning of the track and will always do it the same way!)
2) Some kind of very fast source such as Bitperfect, Audirvana, or even WASAPI feeding a sound card in a particular mode (probably EVENT DRIVEN).
3) I'm becoming pretty sure that it only happens when the Asynchronous transfer mode over USB is being used. If you use a synchronous (i.e., adaptive mode) I don't think the problem occurs. For example, if you are using WASAPI in PUSH mode you probably won't see the issue as I think the PUSH mode is synchronous.
It is as though the DAC reaches a processing "overload" of some type and it triggers the rise in noise floor. The Asynchronous transfer mode probably does much more handshaking than the traditional synchronous (adaptive) modes adding to the overhead.
My big issues with this is that the Asynchronous mode normally eliminates all issues with jitter due to cabling, PC power supply, PC clock, and interrupt service routine overheads in the OS, basically providing some significant improvements in playback for systems capable of revealing that level of detail. Exactly what you would want on a new flagship DAC. If the Asynchronous mode is really contributing to this problem, I'm now forced to either down-sample my hi-rez files or use an older and inferior USB transfer mode (i.e., adaptive) in order to listen to them.
For what it's worth, my guess is that when the glitch happens, the PCM to SDM translation in the DAC might be getting messed up. Since the SDM stream is processed out of the PCM data, it might be sensitive to low volume data patterns in the initial PCM of the track. This could explain why some tracks trigger the issue and others don't. But these are nothing but guesses on my part. Without knowledge of the guts of this product and some logic analyzers to track what's happening in the HDVD800 and the USB connection, we are completely dependent on Sennheiser to tell us what is happening.
One way or the other, 24/192 USB for some Hi-rez files is unusable and I would like to know if this is fixable or not and whether or not it WILL be fixed. If Sennheiser takes no real interest in this, I'm dead in the water with a $2K DAC/amp combo that is limited to useful digital data rates of only up to 24/96 USB (and 24/88.2 for optical).
- Jeff