Quote:
I do understand the problem here now.
I think the easiest fix is to use software. They can provide a checking and converting tool to the user and let the user decide whether or not the "format" the file into HDVD800 readable ones. (Pre applied low-pass filter or file re-formatting). Since it is a change done to the digital source, I do not think we need to do it in real time~~~~~
Just my guess, not sure it is easy as it sounds.
P.S.
Anyone try to adjust the gain switch while using the DAC? Does it do anything funny?
That would be really nice if possible, but the issue might go much deeper than that. Digital signal processing can require extremely fast processing speeds. That's why much of it is done on the big IC chips (e.g., the Burr-Brown converters used in the problem). Customizing ASICs and then retooling for manufacturing is not trivial. Any general software processing outside of the main chips is going to typically be limited in it's capabilities.
And as I've alluded to in my postings, I'm still not really sure exactly what the problem is other than the HDVD800 doesn't handle the excess ultrasonics in some data files. For example, in the spectrograms in post #1083 you can see that the ultrasonic noise on the St. Louis Blues soundtrack is at about -50 dB. Well the music in that track also runs about the same level. (in other words the "volume" of the ultrasonics that shouldn't be there is about the same as most of the music that is supposed to be there). This track created significant hiss. On the other hand the "Stank" soundtrack's ultrasonic data was at -85 db which is only -35 dB below the problem causing ultrasonics on the "St. Louis Blues" track. However it is still 30 db higher than it should be (around -115 dB). Why doesn't it create the hiss?
Maybe it does and it's just much quieter, You'd need instruments to tell. My point is that although I know that noise in the track that is above the Nyquist frequency can produce aliases in the audible range, I'm only posing as Inspector Gadget here. What if the Burr-Brown chips were already designed to handle this contingency? That would mean that something else isn't right.
Here's a great example that has existed occasionally over the years where people have been surprised that an expensive set of interconnects were needed for a fix. What if it is the
analog part of the Amplifier section that is going loopy in the presence of noise in the 85 kHz region? A lot of wide band amplifiers designed as audio amplifiers might have a bandwidth going up to 1 Mhz, however their distortion characteristics were are only monitored in the audible ranges (you're only going to put audio data through it, right?). If Radio Frequency noise picked up in ground loops gets into the front end of that amplifier, you can get audible artifacts. For example, if an RF signal at 900 kHz and one at 901 kHz (both of which are not audible) are present and the amp has a high intermodulation distortion in that range (and I know that many have over the years), one of the intermodulation products you will get is a 1 kHz tone which is DEFINITELY audible!
So there is even a possibility that isn't too extremely remote, that the problem could be in the headphone
amplifier section of the HDVD800. Does the HDVD800 have an extremely low set of distortion characteristics at the top end of the bandwidth? I would hope so but without any spec sheets on the product it is anyone's guess (which is what I'm doing here)
Hence here are a few reasons why I have so much fascination about the current issue. I know enough to be dangerous (as they say)
By the way, this latter issue has resulted in some fascinating design techniques in analog interconnects over the years, usually in how they do the sheilds. One way is the "telescoping" shield. this is where an inner shield carries the signal and a second outer shield carries any RF pickup. The difference is that the outer shield is only connected at the source (i.e., low impedance) end of the cable making it directional. The intent is that RF noise is carried to ground far away from sensitive input circuits. Another one is like Audioquest's approach to as many as 5 shields with a resistive layer of material between them (rather than carry the signal away to ground, just turn it to heat).
DACs are notorious for radiating digital RF noise. One common occurrence is for the noise to travel out along the power cable and re-radiate from there. If this gets onto the interconnect sheilds and then into your power amplifier (which of course is setting right then next to your DAC), you can get intermodulation and other distortion artifacts showing up. If you put a more expensive power cord (which has a shield on it), the radiation from the power cord is reduced significantly and anything that makes it to the wall socket is now too small and too far away to affect anything. So GUESS WHAT? Putting a more expensive power cable on your DAC can actually make your Power amplifier or preamp SOUND BETTER. Go Figure!
- Jeff
P.S. The gain control on the back of the HDVD800 only affects the RCA unbalanced inputs to the amplifier section.
