Cable Distortion Measurements: Part Deux
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 11th January 2004, 07:46 AM #261 mrfeedback   diyAudio Member     Join Date: Feb 2002 Location: Perth, Australia. This thread is named 'Cable Distortion Measurements'......... There are multiple differences between those graphs, and saying "Again, no signs of the high-order harmonics that John says he saw in the set that I sent him." is simply not true. One thing that GLARES at me out of those graphs is WHY are the 4 kHz and 6 kHz harmonics not present when there is harmonic activity at 2kHz, 3kHz, 5 kHz and 7 kHz an all the 13V graphs ???? I this to be expected for a perfect piece of wire ????, or is this an artifact of the measurement sytem ????. Eric. __________________ I believe not to believe in any fixed belief system.
Steve Eddy
diyAudio Member

Join Date: Sep 2002
Location: Sacramento, CA
Re: This thread is named 'Cable Distortion Measurements'.........

Quote:
 Originally posted by mrfeedback There are multiple differences between those graphs, and saying "Again, no signs of the high-order harmonics that John says he saw in the set that I sent him." is simply not true.
It is true. The level of the high order harmonics that John has been measuring have been above -125dB relative to the fundamental. The AP measurements are measuring some 20dB below that (around -145dB) and there's no sign of any high order harmonics at -125dB.

Quote:
 One thing that GLARES at me out of those graphs is WHY are the 4 kHz and 6 kHz harmonics not present when there is harmonic activity at 2kHz, 3kHz, 5 kHz and 7 kHz an all the 13V graphs ????
There's 4th harmonic visible in the 13 volt plots. Not as evident in the jpgs as in the pdf though.

This behavior is rather characteristic of complimentary circuits which cancel even order distortion. You're just seeing the even order distortion products disappear into the noise before the odd order distortion products.

Quote:
 I this to be expected for a perfect piece of wire ????, or is this an artifact of the measurement sytem ????.
It's just the residual distortion of the AP's generator.

se

 11th January 2004, 09:21 AM #263 Christer   diyAudio Member   Join Date: Sep 2002 Location: Sweden Morning guys, last night I posted late and was tired. Now it's morning and I am tired, so maybe I am still wrong. I am not sure what the supposed problem with my comment on cable direction was. I don't believe the direction matters but I cannot really know, so if we want to be scientific about this then direction is a variable which should be controlled, whether we believe it makes a difference or not. On the other hand, if we want to be scientific there is a lot more that would have to be done, having more people repeat the measurements etc. etc. I am not saying we should or have to do that, only that we cannot really know in a scientific manner what the answer to the original question is. What we believe is another thing. Although I don't know anything about the test equipment used, the AP2 seems to be accepted as a reliable piece of equipment so it seems reasonable to me to assume that Brunos measurements are correct and John has some measurement error, but that is a belief not a claim or a truth. Anyway, let's hope SY gets a chance to do his scaling experiments on Johns setup, then we will know more. Eric, correct me if I am wrong but it seems to me you are talking about the audibility of an 0.5dB deviation in frequency response. I don't think that has anything to do with audibility of 0.5dB variations in the distorsion products. I am not claiming anything about what is or isn't audible, just that there is no obvious connection between audibility of the two things. It seems like apples and pears to me.
jan.didden
diyAudio Member

Join Date: May 2002
Location: The great city of Turnhout, BE
Re: Who Listens To Sinewaves ?...............

Quote:
 Originally posted by mrfeedback "Where has it been established that changing the level by 0.5dB over a 1/3 octave bandwidth is clearly audible? And please, no amusing anecdotes." The other night I did exactly this to the FOH 31 Hz graphic eq fader, and my colleage responded immediately by asking what I did - " That's sitting much better now ! - What did you just move ?"[snip] janneman: Wait a minute! We are talking about real minuscule, if at all, cable distortion. Even if your FOH stuff is objectively true, which is not proven, what does that have to do with cable distortion audibility, if any etc? [snip]"And what has the fact that no one to date has yet demonstrated actual audibility of cable direction lead you to think?" This leads me to believe that the appropriate tests have not been performed correctly yet. janneman: Believe is the right operative word here. Another possibility, that I believe, if you will, is that nobody has demonstrated it because it isn't there. [snip] The AP test set is showing load dependency according to the graphs. janneman: this is expected, as different levels and termination affects the noise level and therefor the dynamic range. If we would not see this, we would conclude that something is really wrong or the cables do have distortion and/or noise. [snip]

Jan Didden

(Hope I haven't messed up this text...)

 11th January 2004, 02:02 PM #265 johnferrier   diyAudio Member     Join Date: Sep 2003 Location: WA Of course, this won't satisfy the scientific community... ...but then beyond the possibility that John was always measuring in the wrong direction and Bruno was always measuring in the right direction, you've then got temperature, relative humidity, phase of moon, and you name it. This isn't a government funded "scientific" investigation. And in that case, the results sometimes become forever inconclusive. Maybe people think we are there (but then why waste more time and effort?). However, for a diyAudio investigation, this seems to be as thoroughly investigated phenomena that I've seen (in my brief interaction with diyAudio). Maybe the topic of another thread, but if there are other examples of very thoroughly investigated subjects at diyAudio, I'd be most interested in a link or two... One thing to remember is that, beyond the recent batch of four cables, there was also the batch of three cables in the prior thread. So the possibility of the all right/all wrong directionality goes down even further. Further, neither Bruno nor John make mention that they are aware of any directionality in there use of the equipment. Certainly, if John, Bruno, Charles, anyone else with an analyzer, a cable mfg, etc. has distortion measurements indicating directionality, then a new thread on measured directionality would swipe interest from Steve's thread here. And as others state, I do agree that these measurements are separate from whether people perceive audible differences (again another thread). There may be other measurements that better flush out such phenomena. However, that is up to the people with a vested interest in directionality to show. JF *EDIT: errors*
 13th January 2004, 12:50 AM #266 john curl   diyAudio Member     Join Date: Jul 2003 Location: berkeley ca Folks, let's not quibble here. If Bruno is correct, perhaps there is something wrong with my measurement. I don't know what it is, but Sy is welcome to come by and advise me, or just check out what I do measure. If this is indeed correct then I would branch into another direction as to why the test equipment itself is sensitive to different cables. This would be just as important as the wires themselves, because the input stage of the ST is very much like any analog input stage. This would make many audio input stages suspect of being susceptible to the wire they are connected to. For the record, and to reduce some speculation: I have recently put a .033 RT styrene cap at the output of the audio oscillator to ground, before the cable. This shorts out the 600 ohm source at high frequencies, and reduces the harmonic distortion contribution from the oscillator. It helps a little, but not much. The cable differences still remain.
 13th January 2004, 08:58 AM #267 mrfeedback   diyAudio Member     Join Date: Feb 2002 Location: Perth, Australia. Keep Going John........... Originally posted by john curl Folks, let's not quibble here. If Bruno is correct, perhaps there is something wrong with my measurement. I don't know what it is, but Sy is welcome to come by and advise me, or just check out what I do measure. Hi John, Yes, it seems that a closer look is needed to work out what is going on, and causing these experimental differences. If this is indeed correct then I would branch into another direction as to why the test equipment itself is sensitive to different cables. This would be just as important as the wires themselves, because the input stage of the ST is very much like any analog input stage. This would make many audio input stages suspect of being susceptible to the wire they are connected to. SE excepted, there are a whole bunch of us (millions?) who observe audible differences according to cable type on typical systems. Cable electrical parameters differences are accepted as the explanation, but I agree that output and input stages are part of this equation, and require closer investigation of their behavioral changes according to cable type. I still feel that there is more than just this going on based upon experimentation with the modified cables that I have cooked up - I get the same sonic signature regardless of the cable type (different makes of balanced and unbalanced) that I am using, and the equipment connected. Curiously this applies to power cables and audio multi-core cables also. The magnitude of sonic difference may change acccording to cable or systems, but not the nature of the sonic difference. For the record, and to reduce some speculation: I have recently put a .033 RT styrene cap at the output of the audio oscillator to ground, before the cable. This shorts out the 600 ohm source at high frequencies, and reduces the harmonic distortion contribution from the oscillator. It helps a little, but not much. The cable differences still remain. So you at least have consistent measurement results. I am interested to get to the bottom of this also. Eric. __________________ I believe not to believe in any fixed belief system.

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