Noise/jitter in system, help?

[MaloS]

So I one day plugged in my headphone amp into a guitar just to test the guitar pick-ups (needed to make sure they work), and suddenly realized what i thought was tube noise is not there anymore. ?!
So when I finished testing I plugged the amp back into the Micro DAC I normally use, and hello, the noise is back. Hmm. Pulled it out, plugged it into the computer audio card thinking the issue is with the DAC...same noise. Plugged into mp3 player - only minor hiss that I know is typical of this player cause of the UM2 I use with it.
Back into the comp - jittery noise, annoying. Gaaah.

So how do I get rid of this? I think the source is the computer circuitry, but to be heard from the DAC it must then travel up the USB cord I am using. If that is possible, and is true, than I need some kind of a card with optical output to feed into the DAC, assuming that would resolve the issue. Would it?

Any thoughts?

(I use a power conditioner by the way and I know the noise from the laptop audio output was the same before I had the conditioner).

 

[abs@nilenet.com]

Yes, the noise is more than likely coming from your PC over the USB cable. I had the same issue with my Micro Dac and switching to optical fixed it. The AV710 is a nice inexpensive sound card that works well for me.

Happy Listening!

 

[EnOYiN]

I have never experienced such things, but I think you would want to check it with some other PC's instead of buying a soundcard to use spdif straight away. Since USB is actually better than spdif as far as jitter is concerned I would really think about the spdif option twice.

Aside from these options I just can't imagine that a product like this would not be able to use USB without cracks. It could be that there is something going wrong with the transition from USB to spdif to DAC. Some DACs convert USB signals to spdif first, before going to the DAC. I don't know for sure that that is what the MicroDAC does.

You can always contact Headroom. Maybe they've got a solution.

Edit: USB cables can't really create hiss as far as I know. Here is a post about the USB technology. You will have to scroll down a bit in the thread.

 

[craiglester]

Sounds like a grounding or sheilding issue. Try a different usb cable, a good one, witha choke on it. That may help. Then again it could be the amp, or the interconnect. Test each component by changing only one of the items at a time. when it goes away, you've found the bad one. just make sure you do it one item at a time.

 

[x99]

You sure about that? Most USB products have jitter levels that are much worse than their "regular" counterparts. See, e.g. the review of the HeadRoom Total BitHead done by Stereophile a few years ago. I don't know if the jitter performance is necessarily due to the USB, but it's pretty terrible by modern standards. Even Emu's latests products claim figures that are less than stellar, although I haven't seen any tests yet.

SP/DIF has been around so long that most people have figured out how to do it right. USB is often quite a mess, and to my knowledge, comprehensive jitter tests haven't been done on enough devices to give a clear picture of how well the manufacturers are doing.



Quote:

Originally Posted by EnOYiN /img/forum/go_quote.gif I have never experienced such things, but I think you would want to check it with some other PC's instead of buying a soundcard to use spdif straight away. Since USB is actually better than spdif as far as jitter is concerned I would really think about the spdif option twice.

 

[MaloS]

Well it is definitely not any of the interconnects, I could test that but thats like checking if a cat is going to chase a mouse or not, especially given that all the ICs in use come from Headroom. Also the noise is the same as the laptop itself so its from the laptop like others are suggesting.

My options are not very wild, I am going to try TBAAM with optical out into the Micro DAC in hopes of that doing that trick as it seems to have done it for some. If not I might have to get a transport. (At least Squeezebox is nice =])

 

[Gatticus]

http://www.positive-feedback.com/Issue22/nugent.htm

Contributors to Jitter

There are a number of key components in typical digital audio systems where contributions to jitter is significant, including:

1.

The pits in the CD
2.

Reading of the pits by the optical read-head of the transport
3.

Jitter in the master clock in the transport and Jitter in the asynchronous re-clocking in an upsampling DAC
4.

Transmission of the S/PDIF signal
5.

Dispersion of the signal in the S/PDIF or AES/EBU cable
6.

The electrical-optical-electrical conversions in a Toslink interface
7.

Conversion of S/PDIF to extract clock and data
8.

Noisy power supplies and ground-loop noise

USB and Firewire converters have the disadvantage that they are obviously wired and the wires have length limitations. The advantages include dedicated bandwidth, 24-bit/96 kHz data support, and isolation from the computer and separate power supplies, including batteries. These converters currently allow the highest quality playback.

 

[x99]

Yeah, but you're listening to someone who is about the only human being on earth claiming that USB is a low jitter medium.

Most USB soundcards stink. It's why I originally went with an Audiophile 2496 instead of the USB model four years ago. Perhaps his cards are low jitter, as he appears to use an external masterclock with a TAS1020A or TUSB3200 USB receiver. At least, that's what I assume, or else those $500+ cards aren't much more than a prettied up Transit. Most USB external soundcards don't do that, including, AFAIK, M-Audio's.

And this whole bit about noisy computer arguments is total hogwash. When you can pull 116dB+ SNR with some of the 24/192 internal cards like the Lynx L22, noise isn't much of a factor.




Quote:

Originally Posted by Gatticus /img/forum/go_quote.gif http://www.positive-feedback.com/Issue22/nugent.htm Contributors to Jitter There are a number of key components in typical digital audio systems where contributions to jitter is significant, including: 1. The pits in the CD 2. Reading of the pits by the optical read-head of the transport 3. Jitter in the master clock in the transport and Jitter in the asynchronous re-clocking in an upsampling DAC 4. Transmission of the S/PDIF signal 5. Dispersion of the signal in the S/PDIF or AES/EBU cable 6. The electrical-optical-electrical conversions in a Toslink interface 7. Conversion of S/PDIF to extract clock and data 8. Noisy power supplies and ground-loop noise USB and Firewire converters have the disadvantage that they are obviously wired and the wires have length limitations. The advantages include dedicated bandwidth, 24-bit/96 kHz data support, and isolation from the computer and separate power supplies, including batteries. These converters currently allow the highest quality playback.

 

[Gatticus]

I've used my EMU 0404 as a USB audio device and as an external DAC via SPDIF and can't hear a difference so I beg to differ that USB audio is junk. The computer is electrically noisy so it is always best to use external audio device if you can. That's why external TV tuners are better too.

http://www.audioasylum.com/forums/pc...ages/7719.html

http://forum.stereophile.com/forum/s...48&an=0&page=0

Yes, jitter is a very serious matter with USB. In fact, one interesting piece of information we found (though we did not confirm) is that computer manufacturers will ADD JITTER to their clocks for the purpose of spreading the energy across a wider bandwidth to pass emissions testing. Apparently the spike at the fundamental clock frequency was causing interference of some sort.

The DAC1 USB is well suited to handle this jitter utilizing the same clocking technology that made the DAC1 so successful...UltraLock. With this clocking system, the DAC1 will perform exactly the same no matter how much jitter is on the clock...quite literally. There aren't too many converters that can make that claim, but we encourage you to compare.

---------------------------------------------
I don't know if EMU 0404 has something similar to counter jitter over USB but I would hope so.

Ultra-low jitter clock subsystem: < 500ps RMS in PLL mode (48kHz, Coaxial S/PDIF Sync)

 

[x99]

I said "most" stink..

The EMU's might be an exception, but I don't think they're using asynchrous data transfer with a separate clock either. Presumably they're using a PLL, and while that isn't awful, it isn't great. That said, I'm just guessing. 1st gen USB devices wouldn't do 192, and I have no idea which USB receiver Creative stuck in this thing. Still, they would have to beat the published jitter spec by half to be a real reference-grade device.

As for the Benchmark, I believe it probably reclocks with its own separate master clock. Most USB DACs don't do that, because you have to write your own software and it's rather complex. If they're doing async with USB, that's also why they charge like $400 for the upgrade.

Quote:

Originally Posted by Gatticus /img/forum/go_quote.gif I've used my EMU 0404 as a USB audio device and as an external DAC via SPDIF and can't hear a difference so I beg to differ that USB audio is junk. The computer is electrically noisy so it is always best to use external audio device if you can. That's why external TV tuners are better too. I don't know if EMU 0404 has something similar to counter jitter over USB but I would hope so. Ultra-low jitter clock subsystem: < 500ps RMS in PLL mode (48kHz, Coaxial S/PDIF Sync)

 

[Gatticus]

Maybe I should go back to using my EMU 0404 over SPDIF instead of USB. USB is more convenient for me though.

 

[uraflit]

the emu 0404usb had too many problems for me when used through the usb port, the spidf optical out saved everything.

but to be on topic, if the noise is transferred through the USB port, would a TBAAM eliminate the noise? it's still going through the usb port... but maybe the optical out will get rid of it.. ?_?

 

[regal]

x99 is correct. USB is a poor audio transmission vehicle. The measurements I have seen show huge spikes at 1khz due to this being the frerquency the packets of data are transferred via USB. Note that the overall jitter measurements aren't to bad the problem is its all concentrated right where are ears are most sensitive (1khz).

If you want a good cheap clean digital connection to a computer use Toslink, no ground loops. The jitter is still relatively high due to the noisy powersupply your computer but it is spread evenly across the audio spectrum and not anoying.

If you want low jitter from a computer your only answer is ethernet where the clock is derived separate from the computer's SMPS.

 

[Crowbar]

USB is only poor if your DAC is synchronous with the PC source (and thus analog information, the clock timing signal, gets transmitted over it as well, resulting in jitter problems). That need not be so, though, unfortunately, it's the common implementation. Moreover, plentiful RF noise from the PC gets coupled through pretty much any connection, though can be minimized if you use coax with pulse transformers on both ends. As for Toslink... no. There are measurements at diyhifi and diyaudio that show the optical transmitter and receiver devices used for Toslink have significant intrinsic jitter and are far worse than coax. Even though a PC is very RF noisy, the coax and transformer version is better than this. Pulse transformers are cheap and work very well. If you really want optical, use a laser over glass fiber like some high end transport/DAC systems do, instead of the crappy LED over plastic fiber of Toslink. The jitter of such systems is much lower, and of course they are much more expensive. Not worth it; stick with the coax.

Of course, the alternative is to have a fully asynchronous system, and then the interface jitter becomes irrelevant. I'll post schematics later in the summer as the prototype design gets finalized. USB is perfect for this since, unlike S/PDIF, it's bidirectional (and no, I'm not talking about a reclocking system; all one is sending back is requests for more data).

 

[Euphoria]

Maybe your system is wanna watt more than current PSU