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Thread: Procyon - USB+AS=Noise

  1. #1
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    Default Procyon - USB+AS=Noise

    Hi,

    I just received my new Procyon yesterday (8 days to New Zealand - not too bad).

    Apart from one problem everything is just fine - it is everything I expected.

    The problem I have has been reported here by a number of people, but I have not seen any satisfactory solution posted.

    When using the Procyon to provide visuals using AudioStrobe from NeuroProgrammer 2 while also powering the Procyon by USB there is unnacceptable noise synchronous with the LED operation.

    Details:

    Laptop PC running NeuroProgrammer Pro (latest version as at yesterday).
    The Procyon arrived with the latest firmware (2.1.0)
    Headphone output connected to Procyon Aux.
    Headphones plugged into Procyon output.
    USB cable plugged into Laptop USB/Procyon USB.
    Procyon set to AS Mode.

    It all works perfectly - AS levels can be controlled from NP, volume controls on PC and Procyon do exactly what you expect - except for what could best be described as dirty white noise that corresponds exactly to the flashing LEDs.

    Turning the LED brightness control on the Procyon until the LEDs extinguish stops the noise.

    Unplugging the glasses stops the noise.

    Unplugging the USB cable (running Procyon on batteries) stops the noise.

    Using a powered USB hub betwen PC and Procyon makes no difference.

    Running the Laptop off battery instead of mains makes no difference.

    Changing to a high quality USB cable makes no difference.

    The problems relates exclusively to AS+USB - all other variations are fine.

    There is no noise when running the glasses from a Procyon session while powering the Procyon from the USB and listening to NP directly from the laptop (no AS connection), so I don't believe the Procyon is creating electrical noise on the USB.

    I am a computer engineer of many years experience and after the numerous connection permutations I have tried I am convinced that the noise is generated within the Procyon.

    This is rather unfortunate, as I have particular reason to require this combination, and the featureset of the Procyon that made it appear workable is a key reason for choosing the Procyon.

    I would appreciate confirmation that this is a Procyon problem and advice of anything that can be done to correct it. As I'm in New Zealand sending the unit back is not a good option and I am willing to 'work around' the problem (i.e. use batteries or a separate USB power adaptor).

    Kind Regards,
    Craig

  2. #2
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    Default Re: Procyon - USB+AS=Noise

    Hi Craig;

    The problem I mentioned here, http://www.mindplacesupport.com/foru...read.php?t=476 is what's called a "ground loop". It is actually an issue with laptop computers that has been around for years. It's due to the fact that the wiring in laptop computers has the digital and audio grounds connected. The problem is not with the Procyon, but with the computer.

    I am an audio technician by profession, and it's a widely known problem with using laptops in professional audio. What is done is typically an isolation transformer is used. In the audio industry these are common items that are used to fix ground loops. This problem also exists in car audio where you get engine noise in the audio system.

    Obviously the home user is not going to have isolation transfomers lying around, so the easiest solution is to run the Procyon on batteries. Alternately, you could purchase a USB power supply and run the Procyon on that. Or you could purchase a cheap isolation transformer from someplace like Radio Shack. It might be possible that removing the ground connection on the audio cable connecting the Laptop to the Procyon would also eliminate the noise. I may test that idea when I return back in May.

    Thank you for doing such detailed troubleshooting. If you would like more information on isolation transformers or anything else regarding this issue, please let me know.

    -Andy.
    Last edited by Andy; 04-30-2008 at 02:38 AM.

  3. #3
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    Default Re: Procyon - USB+AS=Noise

    Hi Andy,

    Thank you for your prompt reply.

    I had read the post you referred to, but it didn't quite seem right to me. I should add that I was trained in audio and RF before I deserted and went into computers and the problem I'm experiencing sounds more like a high frequency decoupling issue than a loop problem.

    I don't have any audio transformers lying around (I assume you meant to isolate the audio as I had eliminated mains issues by running the laptop off its batteries) however, based on the understanding that the digital and audio grounds are common within the laptop, I just used a 3.5mm stereo to 3.5mm stereo extension cable and cut the ground connection at one end, connecting only the two signal wires - a strategy common in audio applications. It works exactly the same - AudioStrobe present, NP audio present plus exactly the same noise. Under these circumstances it is clearly not a 'ground loop' as such.

    I have used all sorts of audio mixers and amplifiers, along with USB midi equipment with this laptop and while I have had to deal with mains ground induced hum, this is unlike anything I have encountered before.

    Please understand that I'm not wanting to make an issue of this - I am actually quite intrigued by this problem - it just doesn't quite make sense to me. I might have a play around with an oscilloscope when I've got some time over the weekend. Needless to say, I won't be doing anything to void the Procyon warranty.

    Cheers,
    Craig

  4. #4
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    Default Re: Procyon - USB+AS=Noise

    Just as a by-the-way, lest this be seen as a 'laptop' problem, exactly the same thing occurs on my relatively new, relatively high-end desktop machine.

    Cheers,
    Craig

  5. #5
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    Default Re: Procyon - USB+AS=Noise

    Quote Originally Posted by CraigT View Post
    Hi Andy,

    Thank you for your prompt reply.

    I had read the post you referred to, but it didn't quite seem right to me. I should add that I was trained in audio and RF before I deserted and went into computers and the problem I'm experiencing sounds more like a high frequency decoupling issue than a loop problem.
    It's deceptive, but I assure you that's the way a ground loop sounds with a PC. Nothing like the sort of sound you get with an AC ground loop. A car audio ground loop also sounds nothing like an AC ground loop. First time I heard it I didn't believe it was a ground loop either, but when I used an isolation transformer and it got rid of the problem, I knew that was the only possibility. There are now even specialized "PC" interfaces made specifically to deal with the problem of interfacing PCs with audio systems. Like: http://www.interspaceind.co.uk/produ...oduct.php?id=7 and the "pcDI" from Whirlwind: http://www.whirlwindusa.com/dirbox.html (scroll down) also: http://www.radialeng.com/di-jpc.htm.
    Another solution which may work is to use an external soundcard.

    I don't have any audio transformers lying around (I assume you meant to isolate the audio as I had eliminated mains issues by running the laptop off its batteries) however, based on the understanding that the digital and audio grounds are common within the laptop, I just used a 3.5mm stereo to 3.5mm stereo extension cable and cut the ground connection at one end, connecting only the two signal wires - a strategy common in audio applications. It works exactly the same - AudioStrobe present, NP audio present plus exactly the same noise. Under these circumstances it is clearly not a 'ground loop' as such.
    Yeah, for some reason lifting the ground on the signal line sometimes does not work. In these cases an isolation (signal) transformer is the only solution to fix the ground loop.

    I have used all sorts of audio mixers and amplifiers, along with USB midi equipment with this laptop and while I have had to deal with mains ground induced hum, this is unlike anything I have encountered before.
    I understand. It does sound different.

    Please understand that I'm not wanting to make an issue of this - I am actually quite intrigued by this problem - it just doesn't quite make sense to me. I might have a play around with an oscilloscope when I've got some time over the weekend. Needless to say, I won't be doing anything to void the Procyon warranty.
    I'd be interested to hear what you find.

    I just did a little test of my own. Using a USB power supply instead of plugging the USB into my laptop fixes any noise issues. BTW - in my case the noise that followed the lights is extremely low. It was only audible when I plugged the Procyon output into an amplifier and boosted the signal considerably. Adding any audio to the signal completely masked it. But, even that little noise completely disappeared once I unplugged the USB connection from my Laptop and connected it to a USB power supply.

    -Andy.
    Last edited by Andy; 04-30-2008 at 04:59 AM.

  6. #6
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    Default Re: Procyon - USB+AS=Noise

    Again, thank you for a quick and detailed response.

    I have also confirmed that a separate USB power supply solves the problem.

    For now I'll just use that as a workaround, but I'm not happy - this problem is just begging for an elegant solution and I will persevere in finding it.

    Cheers,
    Craig

  7. #7
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    Default Re: Procyon - USB+AS=Noise

    Hi Craig;

    I fear you may not be able to find a simple solution... but this will work: http://www.radioshack.com/product/in...entPage=search

    Replacing the RCAs with TRS 1/8" connectors will do the trick. That may or may not be an easier solution if you don't want to use a separate USB PSU or batteries.

    As I mentioned, this is not a new issue and has been around as long as there have been PCs interfacing with audio equipment. I hope you don't spend too much time on this. I'm sure you have more interesting things to do!



    -Andy.

  8. #8
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    Default Re: Procyon - USB+AS=Noise

    Thank you for that link - that looks like a good, low-cost solution that would almost certainly do the trick.

    However, I have found another solution - a simple LC filter built into an old USB hub - cleaning up the USB 5V, removing the noise created by the rapid switching of the Procyon works just fine too.

    Thanks heaps for your assistance.

    I'll now get on with enjoying the little beasty.

    Cheers,
    Craig

  9. #9
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    Default Re: Procyon - USB+AS=Noise

    Filtering the USB power is not a good idea - there is a reason why the USB specification sets a limit for capacitance on the load. Unfortunately my filter causes the laptop to reboot occasionally.

    What I have now done is make up a USB Y-cable that allows me to connect USB data to the laptop while taking power from an external adaptor.

    This allows me to run sessions directly from the editor and avoid all power issues without having to chew up batteries.

    Cheers,
    Craig

  10. #10
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    Default Re: Procyon - USB+AS=Noise

    I think these will be my last words on this subject as I think I've exhausted all reasonable possibilities.

    I have now tried a low cost audio transfomer similar to the Radioshack one in one of the links above. It gets rid of the noise alright, unfortunately it does this by preventing AudioStrobe from working at all - it doesn't have a high enough frequency response to let the AS signal pass. A better quality unit may do better but...

    I have had a good look at where the noise lives with an oscilloscope - everywhere! It is created on the USB power by the high speed switching of the LEDs. It is differential, not common mode (both on the power and audio) so I wouldn't expect audio transformer isolation to be effective, and why filtering the USB power does work, although at the cost of exceeding USB load specifications, with associated risks of rebooting or damaging the laptop's USB port. While some potential difference can be measured between different ground points the 'ground loop' potential is insignificant compared to the differential noise.

    As it is load induced noise it would seem that a separate power supply is the only viable option, with the Y-cable described above being a good solution that allows convenient use without having to swap data and power connections back and forth.

    Naturally, I only know this to be the case for my problem with my configuration - noise is an insidious beast and may well arise in other ways, with other solutions for other people.

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