Null Difference Testing

[fdegrove]

Hi,

But interconects in audio and speakers cables don't work as transmission lines(if they work they will need matched impedances at the sending and receiving end)...

Matched impedances is not a requirement for a transmissionline to exist.
This is precisely one of the problems with audio design, you don't have a fixed standard for impedances other than a digital line as you point out.

A simplification of a model:

Cheers,

[Tube_Dude]

Matched impedances is not a requirement for a transmissionline to exist.

The rule for transmission lines is that the load (and possibly the source) should present an impedance equal to the characteristic impedance of the line...
The line is then "matched"...

This is precisely one of the problems with audio design, you don't have a fixed standard for impedances

No itsn't ...because for audio the signal source should have a source impedance small compared with the impedance of the load being driven and that the load should present an input impedance large compared with the source impedance driving it!!!

Anyway...what have transmission line theory to do with a null test for audio???

[phase_accurate]

A transmissionline is a transmissionline and stays a transmissionline independant of source or load impedance. Though the proberties of the whole arrangement will change.

It works best however if it's own impedance (I don't have the correct expression on hand, in German it is "Wellenwiderstand"), the source impedance and the load are matched.

For our audio equipment it is indeed usual to have low source and high load impedances, wich is handled more easily by the electronics but is nonideal regarding signal transmission in cables.

If you want to compare cables then you HAVE to take the effects, generated by said cable's properties as transmissionline, into account.

Regards

Charles

[nw_avphile]

Originally posted by phase_accurate
If you want to compare cables then you HAVE to take the effects, generated by said cable's properties as transmissionline, into account.

Except Tube_Dude is correct, the transmission line issues don't matter below 20khz! I challenge someone to show me a measurement of any cable artifact that can be reproduced with typical cables and equipment AND can be argued is audible (i.e. it's amplitude is greater than -70db below the signal).

I also challenge anyone to a blind listening test comparing any reasonable cables to the Radio Shack variety. You'll fail just like everyone else has.

[nw_avphile]

Originally posted by janneman
Yes, but on the other hand, if you cannot hear any differences even with the imperfect nulling test, as has been stated by some, what are the chances that there is a real difference, masked by the residual nulling error, that you CAN hear (the subtle cable differences) in a normal listening session?

My own tests show that a null of -50db is sufficient for most people not to hear a difference in blind listening tests. I extend that to -60db to allow for people with really exceptional hearing/listening skills. Bob Carver claimed he managed a -70db null in the Carver Challenge which fooled the ears of the Stereophile editors.

So somewhere between -50db and -70db null I believe we can safely say there are no audible differences to be heard. So, yes, if the amplifier is only managing -40db or -50db by itself, it may well mask differences in the cables. If it's closer to -70db, however, I'd have to say the null is sufficiently deep to argue the two things being compared will be indistinguishable in a blind listening test.

As was discussed a bit in the other thread, the more accurate way to do this would be to "weight" the null results (something like A weighting for S/N measurements) according to human hearing sensitivity. A poor null at 20khz is less likely to be audible than a poor null at 500hz.

[fdegrove]

Hi,

Except Tube_Dude is correct, the transmission line issues don't matter below 20khz!

If I recall correctly:

Weren't you the one claiming that some cable manufacturers were deliberately introducing cables that were "distorting" the signal by introducing a filter that made them roll off at 20KHz?

If you need to make such bold claims, can't you at least TRY to be consistant?

And transmissionline anomalies do cause havoc in even your audible range unless phase delays and other deviations from linearity are inaudible to you.

No offense, but please refrain from spreading nonsense.

Cheers,

Cheers,

[Tube_Dude]

And transmissionline anomalies do cause havoc in even your audible range unless phase delays and other deviations from linearity are inaudible to you.

So for you interconects must be considered transmission lines ...so for a load impedance of 47k the cable feeding it must be a 47kOhms intrinsec impedance...

What about a digital cable for interconect??...it was built for to work as a transmission line...well...but only with 75 Ohms load!!!

It's amazing!!!

No offense, but please refrain from spreading nonsense.

But who is in reality spreading nonsense here???

[nw_avphile]

Originally posted by fdegrove
If I recall correctly:

Weren't you the one claiming that some cable manufacturers were deliberately introducing cables that were "distorting" the signal by introducing a filter that made them roll off at 20KHz?

If you need to make such bold claims, can't you at least TRY to be consistant?

And transmissionline anomalies do cause havoc in even your audible range unless phase delays and other deviations from linearity are inaudible to you.

No offense, but please refrain from spreading nonsense.

Fdegrove: Show me the proof of the "nonsense"? You've yet to do that despite the question being posed several times. So I could just as easily request you refrain from spreading unproven myth. At least the objective facts and many well documented references support my statements.

As for being consistent, the sorts of transmission line effects being discussed here (reflections, impedance matching, etc.) have nothing to do with the simple RC network roll-off I referred to earlier. They're apples and oranges. If you don't understand the difference, you might want to read up on the subject.

As for my "bold claims", I'd suggest those with an open mind check out the information at this link:

http://www.svconline.com/ar/avinstal...bles_critical/

The link above discusses the very issues we're talking about. Please take particular note of the references at the end--something the subjectivists here like fdegrove are entirely lacking to support their arguments.

So... do we believe the opinions of non-blind listeners clouded with psychological bias and those who have a vested interest in maintaining the status quo in high-end audio (fdegrove appears to be one of them as he claims to be a high-end cable "designer"), OR do we believe the results of carefully run, documented and published blind listening studies and other objective evidence?

It's your choice.

[fdegrove]

Hi,

If you must insist on the topic:

Anyway...what have transmission line theory to do with a null test for audio???

I'll repeat it for the last time:

You don't need matched source and receiver impedances to have a transmission line.

And yes you could use a cable designed for digital transmission as an audio cable.
Whether is would sound good is another matter, but work it will.

FWIW, a digital cable is nothing more than a constant impedance coax.
When hooked up in a digital system the termination is done inside the gear involved, a transport and a DAC for example.
If I'm not mistaken the impedance standard is 50 Ohm, I am not really into digital design so I may be off.

Ciao,

[fdegrove]

Hi,

NW,

The link you inserted points to a commercial website which does not constitute scientific proof in my book.

Systems designed to produce subjectively pleasing and distinctive coloration appropriately belong in the recording studio where, like musical instruments, they can be manipulated by artists and producers to generate the desired effects.

These cables don't even belong in a studio either, an musician may use those if it pleases him.

I believe, however, that the ultimate goal of a music reproduction system is as much transparency and neutrality as science will allow.

Now here I fully agree.

Why you insist on labelling people as subjectivist is beyond me for I strongly believe audio is a science and the listening to it is a subjective experience.

Unfortunately a lot of the science that goes into it is not widely, or even not understood at all.

Cheers,

P.S. There is nothing artistic about designing good cables, unfortunately a lot of so called designers jumped on the bandwagon hoping to make a quick one.