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In Reply to: Measurements performed by a friend. posted by Al Sekela on April 12, 2006 at 13:33:25:
I've seen this used to test long lines, you return a "blip" wherever there is an impedence mismatch... so sya you have a two mile run of communications wire, you originate a pulse and then watch the echos, you should only get one echo at the termination, if there are other minor blips returning before the end blip you may have cable flaws.... it's pretty much a clear demonstration of termination and cable length effects...here's a jave applet so you can play with this concept:
http://www.eecircle.com/applets/018/TDR.html
Anyway.... the ONLY way TDR could work is that conductive materials are subject to internal reflections... the practical issue is that audio cables are too short for most testing arrangments...
I think that the TDR phenomena clearly show that energy reflections between impedence shifts (termination, solder joints) are a real phenomenon that few manufacturers confront directly, except perhaps MIT and Transparent...
Follow Ups:
all of the possible resonant modes of the stuff at either end of the cable, and how audio frequencies may be modulating this mess, nor how modern devices may be capable of amplifying the residues... isn't that a large part of why Spectral engineered super high bandwidth gain circuits, effectively so they would pass through whatever HF-RF crap rather than acting as a selectively reflective wall... the entire Spectral philosophy appers to be that it is better to allow energy at all scales to freely move from one end of the sytem to the other rather that have local reflective effects... then it became MIT's engineering problem to very carefully manage impedence shifts at the end of the chain and on the ICs, something that would be a disaster with a simplistic ferrite deflector. Others, incuding HP, have claimed that Spectral actually sounds much better with network-less conductors like Nordost... my hunch here is that maybe the Z-cable products that use the ERS RF couple-and-drain method may work as well or better... less junk sitting on the line itself.
I had not thought of that before, and I don't have insight into Spectral's design philosophy, but it makes sense that circuits with LINEAR behavior in the RF will not be mixing RF noise with the audio signal.You are right that electrical noise is either reflected or absorbed. Reflecting the RF noise, whether from shielding or a low-pass filter, only sends it to where it may do unexpected harm.
besides being crystal boundary free, the van den huls by far have the nicest "deep inner voice" of any IC I have ever owned or heard... yes they have other limitations, but having lived with the killer midrange of carbon it is hard to listen to any other material, except the Cerious... I also am now suspecting that carbon has much lower HF/RF ringing and accomplishes this with much greater elegance than any network solution possibly can.... all metals sound zingy and obscured now....
The self-resonance fundamental frequency of a meter of audio cable is around 50 MHz, which is well within the capabilities of even old HP (before Agilent) gear.
The best equipment in the world can be used incorrectly by anyone, test results can be misinterpreted.Articles can be written by "names", and yet be pure garbage.
It would have been nice to have peer review of this "data".
Nothing is learned otherwise..that's my issue here Al..not you. Sorry if I come across strong, but your actions and those of your "friend" are sub standard, shall we say?
Cheers, John
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