This soundcard's analog section is truly a P.O.S. The output sections, although, if glowingly described by high-end audio wanks "all discrete"... is unfortunately exactly that. Each output consists of a single transistor, resistor, coupling capacitor, and perhaps a rfi-decoupling inductor (?). Basically a class-A stage ( http://sound.westhost.com/jlh_fig1.gif fig a) with no negative feedback to compensate for the transistor's nonlinear transfer function. For the "high quality headphone out" they splurged and used 100uF coupling caps, instead of 47uF!! (woo!). I don't know about you but if i have to listen to a devices transfer function, without negative feedback, I'll take a vacuum-tube: http://ixbtlabs.com/articles2/aopentube/index.html (this has got to be the stupidest mobo i've ever seen -- has a vacuum tube onboard!) FYI, to revel in this $0.99 design, ogle photos of the "mediatek 1723" which is the same card: http://www.pcresource.co.th/html/product/karaoke/images/mediatek_1723/1723_gal_800_2.jpg http://www.pcresource.co.th/html/product/karaoke/images/mediatek_1723/1723_gal_800_4.jpg http://www.9final.com/computer/mediatek-1723-sound-51-channel-with-wavetable-connector-p-2084.html All in all the analog section is crap, and they use a low-end vt1616g codec despite the 24 bit capabilities of the Via 1723.... (which should be fine for re-A/D-ing the sound of the db50xg. which also has a 18bit DAC... but it sounds less good than it could). Fortunately, this $0.99 ebay soundcard has a working SPDIF output, and a solid-click to it's TOSLINK plug, and a bright LED that has no problem going through a $10.00 mechanical optical cable switch unlike the ASUS toslink output module from the motherboard (which unfortunately cost a lot more than the damn $0.99 soundcard). Also the mobo toslink means snd_hda_intel versus snd_ice1724 -- the $0.99 option wins for using this as a TOSlink output card. On Tue, Jun 8, 2010 at 6:13 AM, Monty Montgomery <xiphmont@xxxxxxxxx> wrote: >> The stuff around 14 kHz in R is strange. It's noise, not a >> single frequency interference. No idea where it comes from. > > Last time I saw a random peak that strong, it turned out to be a > byproduct from an opamp that was underdamped and self-oscillating at > about 10MHz... It moved around just a little bit as the oscillation > wasn't itself entirely stable. Complete shot in the dark, I do't > expect to ever see it again (except in homebrew designs that are > slapped together without alot of design analysis). The real mystery is that peak happens when all "capture" inputs are "off" -- I would would have expected that "off" to actually mean the A/D converters aren't listening to the input at all. All the different inputs pass through a resistor and 10uF 25v electrolytic cap and go directly into the vt1616g codec, other than the 1/8" microphone input which uses a single op-amp (tda-1308). If I wanted to waste more time on this (which i don't, I've moved on to a different consumer soundcard), I'd try using shorting-plugs on all the analog ins, as well as shorting on the cd/video analog connectors on the card. And by the way, when using the onboard digital mixer as the input source (as opposed to selecting the specific source to turn on "capture") the noise of the various inputs seems additive making this mode of using the card even worse. Niels http://nielsmayer.com PS: this is interesting: http://stephan.win31.de/soundk.htm _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
