On Wed, Jun 9, 2010 at 12:37 PM, <fons@xxxxxxxxxxxxxxx> wrote: > Looks decent. If some of the small peaks in the LF plots are > mains related, you grid frequency seems to be 115 Hz... I actually checked that peak at 116hz and figured it couldn't be the rectified result of the US-grid 60hz AC. That means we'd be running at 58Hz. ?? Since that's unlikely, what's the likelyhood of a 2hz frequency error in jaaa?? > 'Canonical' settings for this chip are 0x7F (127) for input and > output. The range 128-163 is used by some cards to control additional > input gain. 127 causes clipping. [[side-annoyance: why do some cards clearly light up the red "overload" LED on the external DAC, and this Terratec DMXFire doesn't? I end up using 'qarecord --jack' as a meter w/ a clear red overload indicator that i can actually see, but I wish there was a simple Qt notification-area gadget that would just turn red when you overloaded an input or hit 0db]]. > Changing the caps (if they are indeed that old) could help. Indeed. The card has stickers on it indicating it was produced in 2003. How old is too old for a decoupling electrolytic?? Have any suggestions in place of the no-longer available http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=ECE-A1CN221S ?? And having to resort to something like this seems pretty wanky for a $20.00 soundcard: http://www.tnt-audio.com/accessories/auricap_e.html >> Perhaps the input op-amps on the Dmx6fire are "slew limiting" > Could be, but that would be quite bad design. In particular if > that card can do 96 kHz as well, as I assume it does. It's not really an issue of "bad design" it's an issue of compromise at a given price point. How much bandwidth does the op-amp have, and how much negative feedback is being applied? But a wide-bandwidth op-amp is going to be intrinsically noisier.... and a quiet op-amp is going to be intrinsically slower, and improving either makes them expensive. Actually, one of the improvements people get out of replacing op-amps is IMHO the output slew-rate and overall bandwidth spec. Thus the stock JRC4580 opamps on the Audiotrak Prodigy HD2 are socketed, and upgradeable: http://www.head-fi.org/forum/thread/322497/audiotrak-prodigy-hd2-opamp-configurations-list has a lot of mention of bass "punch" and "control" improvements from replacing the op-amps as well as making the highs less shrill. If you really want to go overboard, they have discrete replacements for these op-amps: http://www.itemaudio.co.uk/prodigy_hd2.html http://bursonaudio.com/burson_opamp.htm > I can't really comment on 'subjective' descriptions. Since you > are quite emotionally involved, and this is not a blind test, > chances are 99.99% that 'it's all in your head'. Or you prefer > lower quality sound :-) Here's the "before" : http://nielsmayer.com/DjColtraneRexx-qchord-salsa.flac (sorry, there's some overs, this is before i learned of the dynex dx-sc51's easily overloaded waveblaster input, combined with potential for large outputs from the Yamaha db50xg (actually NEC XR385)). At some point I'll have both soundcards installed in two difft computers and two different NEC XR385 synths (got a second one for my son coming over from china for $13.00 + 5.50 shipping) and I'll have two files to listen to incase you want to hear what "punch" versus "lack of punch" sounds like. I don't have time right now to go find the section of MIDI I used earlier and re-render using the new soundcard.... eventually I'll post a followup to this thread w/ more results. > If an electronic circuit does things like 'removing (or adding) > punch', that must be explained. There is a limit to what simple > circuits can do, and whatever they do can and should be measured. I agree that when it comes to measuring electrical signals (as opposed to human perception of sound, or any human interpretation of the world around them) there is no place for handwaving, mysticism, etc. Unfortunately, the science of perception is wholly unfounded and mostly bogus if not outright scientific fraud, thus leaving plenty of room for every kind of interpretation. [[ please read and understand this book before having too much of a knee-jerk reaction to my statement http://books.google.com/books?id=2sRC8vcDYNEC&printsec=frontcover&source=gbs_v2_summary_r&cad=0 // http://books.google.com/books?id=2sRC8vcDYNEC&dq=understanding+computers+and+cognition ]] However in this case, my hypothesis is simple. No handwaving, hermeneutics or mysticism is needed. Coupling capacitors induce a low frequency phase shift that is usually ignored because "engineers" incorrectly care only about real-plane/power information; it is misguided to think that humans cannot perceive phase information and "imaginary plane" information. More simply put, in reproducing a picked electric bass, you expect the the "pick noise" (high frequency) to arrive at the exact same time as the the onset of the low-frequency fundamental of the note. The coupling capacitors delay this onset. The simultaneous overlay of fundamental "attack" and "high frequency pick/plucking" onset is what gives a bass it's "snap" and "pop". If you delay the attack of the low-frequency fundamental, you get two sequential softer attacks, and you get a bass sound that is "muffled" "round" or "anemic"... A feeble analog output circuit might not be able to dump enough current out of , or into, the coupling capacitor to allow it to quickly transition from the lowest to highest voltages within the output swing. And there may be stray inductances on the circuitboard or in the capacitor itself that induce oscillations. In which case the output impedance of the op-amp needs to be linear at both low and high frequencies in order to damp out oscillations. Those are precisely the characteristics lacking in low-cost op-amps. So, unless gain is needed, perhaps the cheaper soundcard gets the best sound since it has no op-amps, no bandwidth limitations crossed with negative feedback, no output slew rate limitations, etc. Just a capacitor and resistor in front of an 18 bit ADC. Since a single device inches away is driving the Codec, there really is no need for the op-amp electrically -- there's already an output op-amp and coupling cap on the db50xg (probably a JRC4580) after its 18bit DAC. > If subjective claims turn out to be reliable (and this can be > verified only by blind tests), there will be something that > can be confirmed by measurement. More interestingly, since I'd rather get away from the subjective and back towards the measurable, what kind of tests would be an appropriate predictor for the "bass punch" of a soundcard? Certainly not the frequency response or noise characteristics. More likely it would involve something like reproducing a low-frequency full-voltage squarewave, and observing the slew rate and ringing response caused by bandwidth limitations in the op-amp combined with it's own negative feedback.... -- Niels http://nielsmayer.com _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
