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To optimize the sound quality of an USB-DAC (including CORDA ARIA)

Discussion in 'Headphone Amps (full-size)' started by jan meier, Mar 17, 2006.
  1. Jan Meier Contributor
    Dear headfellows,

    It is now 3 months ago that the CORDA ARIA hit the market and the amp has shown to be a tremendous success. Especially the sound quality through the analog inputs the amp has received many positive comments.

    The comments on the sound quality of the USB-DAC were not all that unanimous. Whereas some people attested a sound quality superior to that of a decent CD-player other people found the sound flat and liveless. However, going into more detail with the new owners it was found most of the negative comments were caused by non-optimal settings of their PC.

    If therefore feel it’s a good idea to make a list of “possible errors” that allow people to check whether their system is working optimal. I have to admit that I’m not an expert in PC-Audio so my comments will be rather limited. I hope people with more expertise will join this thread and add their own ideas, experiences, comments, ….

    Of course this thread is not limited to experiences with the CORDA ARIA only. Any USB-DAC will react very similar to such optimisation efforts.

    **
    While using an USB-DAC like the ARIA it is possible to control the sound volume in three ways.
    1.Change the analog amplification factor by the volume control on the ARIA.
    2.Change the digital amplification factor in the media-player.
    3.Change the digital amplification factor in the sound card device settings in the operating system.

    The problem with digital volume control is, that the effective resolution of 16 bit is strongly reduced. Consider a sample that is digitally lowered to 25% of its maximum value. Mathematically this implies the removal of the two right bits and adding two zero bits to the left.

    Original sample

    0 1 1 0 0 1 1 1 0 1 0 1 1 0 1 1

    Image sample send to the USB DAC

    0 0 0 1 1 0 0 1 1 1 0 1 0 1 1 0

    The effective resolution now has become 14 bit!!

    Therefore always set any digital volume control to maximum! Volume should only be controlled by the analog control on the ARIA / sound card.

    In this connection it should be noted that the default volume value of the standard USB-DAC driver in Windows is 50% and that it does not keep its value in memory. Everytime your computer is restarted (or if you change your sound device) will this value be reset to 50%. Before you start an application always check this value first!!

    **
    The standard Window programs use a sound-mixer that blends together the signals of various sources to one output signal. This mixer is known to effect sound quality, even if only one single source is active. The output of the mixer is not a one-to-one bitcopy of the input signal. ASIO and FOOBAR are said to solve this problem but not all versions seem to work. I’m not knowledged with these programs so people with more expertise are asked to add their comments.

    **
    In a few situations, using inefficient headphones and a very soft recording people feel the need to have a slightly higher gain factor than offered by the standard version of the ARIA. Of course it’s possible to increase the gain factor of the amp by a hardware modification but this may result in poor volume control using high efficient low impedance headphones. A better solution is to change Foobar's replaygain. It allows to boost the gain on quiet tracks.

    **
    Sometimes pops and clicks are audible. Most of the time this results from timing problems in the computer.

    One comment of an user:
    “The first solution was the rather drastic step of changing operating system! I installed Ubuntu (a distribution of Linux) and the issue vanished. Windows is still my main OS however so I was pleased when I installed my new Dell 2405FPW, 24" widescreen monitor. This monitor has two conveniently located USB ports located on the side. Using this USB socket seems have improved things greatly.
    Anyway, if people have the same issue as me, you might want to suggest using a powered USB hub, high end monitors often have them built in, or switching to Linux!”

    **
    Digital equalizer can be very helpful with certain recordings and/or setups. However not all equalizers are of the same high quality. This was written by another customer:

    “After I made sure that no programmatic frequency adjustments were applied on the digital audio, I was able to get very equivalent result out of both audio sources. However, even a tiny adjustment using a digital equalizer on the laptop resulted in a dramatic loss in sound quality.”

    **
    Cables do make a difference. One customer reported that the standard USB-cable placed close to his monitor (non-TFT!) resulted in clear background noises. Using a different cable cleared most of the problems.

    **
    As for ground loops, the ARIA has a built-in ground loop breaker. If only one source is connected this effectively prevents humm. However, if both an analog source and a PC (through USB) are connected then still a ground loop may result. If humm exists you may try disconnecting one of the sources. Even with no humm present this may well improve sound quality!


    **
    Various customers have reported that background noise heard through the USB-DAC can be reduced by deactivating the microphone in the K-Mixer.

    **
    A few links:

    http://www.head-fi.org/forums/showth...ight=pops+aria

    http://m-pulse.m-audio.com/articles/...mization2.html

    http://www.aqvox.de/Asio-USB-Audio-installation.htm


    **
    Your comments are welcomed!

    Cheers

    Jan
     
  2. JaZZ Contributor
    [Bump]

    Thanks for the advices, Jan!

    Quote:

    Originally Posted by Jan Meier
    ...Especially the sound quality through the analog inputs the amp has received many positive comments.



    ...and justifiedly so. The Aria is a very special amp -- exemplarily honest and lively -- and one of the great bargains.
    .
     
  3. JaZZ Contributor
    And you know what? After this experience I'm looking forward to an even more «high-end» Corda with similar sonic virtues and increased refinement... [​IMG]
    .
     
  4. ronniekn
    Thanks for your take on things Jan, I'll definately be looking into that when my Aria Corda arrives [​IMG]
     

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