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Old 3rd August 2012, 02:06 PM   #4751
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Ian, forgetting the hypothesis of contact bounce, do you have any direct experience comparing your 20 yr. old pot to anything? There is a wide audience for stepped attenuators, TVC and AVC volume controls, that extends well beyond this thread. Is the entire market for such things a hoax? I'm a parts supplier to high end audio OEMs. Through a fairly broad survey I've encountered more than a few OEM designers who believe that above a certain level of refinement, most of difference that can be heard between top preamps resides in the volume control.

It's disputable to assert that the properties of the volume control used in playback are undercut by the pot used in recording. For most audiophiles, through many tweaks and upgrades it becomes obvious that the "weakest link" theory doesn't really apply to high-end audio. The recording and playback chain is full of weak links and the gap between recorded and live music is large enough that an improvement in almost any area is perceptible.

It is certainly reasonable--and particularly reasonable to a EE-- to limit experiments to those that he considers reasonable.

Last edited by David Garretson; 3rd August 2012 at 02:35 PM.
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Old 3rd August 2012, 02:17 PM   #4752
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Originally Posted by DF96 View Post
I think I know why some people prefer LDR attenuators. It is for the opposite reason from what they think. Others may simply prefer what they regard as an 'anti-establishment' position: if EEs like it then they are against it. Each to their own.
That's barely even a hypothesis, just a guess for which you produce no evidence. Ian Miller BTW uses that most irritating of ploys, argument from authority [I'm a degree-qualified engineer (in?) and I want to see a paper with a long title because I KNOW you're wrong].

I use an LDR device for volume control because it sounds better than the stepped attenuator I was using previously; the difference is not trivial. I'm sorry if you can't replicate my results but I don't see how entitles you so carelessly to dismiss those who can. I'm not suggesting that the very best conventional devices would not knock spots of my Lightspeed-type device but, on cost grounds, I'll not be finding out any time soon. LDR devices can be had relatively cheap.

Without accepting much of the tosh put about by "audiophiles" and unscrupulous vendors, recall that the history of audio reproduction provides several examples of phenomena initially dismissed by engineers as absurd that later prove to have merit. The best known is perhaps that different capacitors sound different - no doubt you recall the scorn directed by engineers at those who first argued the point. The phenomenon has, of course, since been given a sound empirical basis by makers and designers of capacitors aimed at the audio sector. Thankfully, they eschewed pop psychology and focussed on what they do best.
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Old 3rd August 2012, 03:23 PM   #4753
DF96 is offline DF96  England
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Quote:
Originally Posted by Ryelands
That's barely even a hypothesis, just a guess for which you produce no evidence.
It is a hypothesis. An educated guess is the source of most hypotheses. I have produced as much evidence as those who claim that LDR attenuators are good.

Quote:
Originally Posted by Ryelands
Ian Miller BTW uses that most irritating of ploys, argument from authority [I'm a degree-qualified engineer (in?) and I want to see a paper with a long title because I KNOW you're wrong].
He did not. He simply asked for peer-reviewed evidence or reasonable explanation, the normal standard in science and technology. No length of title was specified. If I read him correctly he is saying "I think you are wrong but I am willing to be convinced otherwise so show me the evidence". As is often the case in 'high end' audio all he was offered was a mixture of anecdote and sneering.

Quote:
Originally Posted by Ryelands
I use an LDR device for volume control because it sounds better than the stepped attenuator I was using previously; the difference is not trivial.
You will accept, I am sure, that this does not refute my hypothesis. It could serve to confirm it. I would expect a small but non-trivial difference, measurable as low levels of low order distortion.

Quote:
Originally Posted by Ryelands
The phenomenon has, of course, since been given a sound empirical basis by makers and designers of capacitors aimed at the audio sector.
It might be more accurate to say that the phenomenon has been given a sound scientific basis by makers and designers of capacitors aimed at the precision industrial sector.
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Old 3rd August 2012, 05:09 PM   #4754
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Originally Posted by DF96 View Post
An educated guess is the source of most hypotheses . . . I have produced as much evidence as those who claim that LDR attenuators are good.
Sorry but it wasn't an "educated guess", it was two instances of run-of-the-mill pop psychology. Firstly, though I'm not exactly sure what you mean by "LDR non-linearity and distortion", to say "probably mainly second, so fairly harmless" is, of course, to guess, not to submit evidence.

Secondly, and more critically, "It was established back in the 1950s that some people prefer sound with a little addition of low order distortion . . ." is misleading unless you can show that the "some" who preferred all those years ago a little distortion with their soup can safely be included in the same group as those who today prefer LDR volume controls. Almost by definition, they can't be.

In passing, I'd add to David Garretson's useful points that those who "claim that LDR attenuators are good" have designed, built and used products, often over a period of years whereas you've made a couple of blanket statements which, on examination, turned out to be pretty much plucked out the air. That doesn't make you wrong - but it doesn't make you very convincing either.


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He did not. He simply asked for peer-reviewed evidence or reasonable explanation, the normal standard in science and technology. No length of title was specified.
The length of title bit was, as I hoped was obvious, a quip, a light-hearted dig at what I saw (since you force the issue) as Millar's heavy-handed, not to say pompous, prose. If it wasn't obvious, I apologise. That said, he made no reference to peer review, in any case a notoriously poor index of a paper's technical merit.


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If I read him correctly he is saying "I think you are wrong but I am willing to be convinced otherwise so show me the evidence". As is often the case in 'high end' audio all he was offered was a mixture of anecdote and sneering.
I don't think you do read him correctly. His question was framed in a manner that borders on solipsism, which was why it irritated me. The first (and, arguably, the only) resort to sneering was his, not mine, in his use of phrases such as "would you care to substantiate the basis of the belief and/or direct your followers . . .". That suggests to me a determination not to be reasonable, not at any price.


Quote:
You will accept, I am sure, that [my preferring LDRs to SAs at my price point] does not refute my hypothesis.
Of course it doesn't. But it doesn't support it either, not least because Millar was discussing elderly pots of conventional design.


Quote:
It could serve to confirm it. I would expect a small but non-trivial difference, measurable as low levels of low order distortion.
IIRC, pertinent distortion measurements have been reported on this thread but I could well be wrong and do not plan to look. Whatever, you can expect a host of things and George S a barrow-load of different ones but a good start, if you're serious about the topic, might be to ask for subjective reports of what differences users hear between the two technologies to see if they lend any support to your notion that enthusiasm for LDRs is essentially a re-run of an uncited result from sixty years back.

Note also BTW that Millar is implying that suppliers and users of LDR-based devices have about them something of the cult whereas you are suggesting only that they like a touch of second-order distortion which, you're guessing, is to be found in this application. The arguments are very different, yours having the merit of not being offensively phrased.


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It might be more accurate to say that the phenomenon has been given a sound scientific basis by makers and designers of capacitors aimed at the precision industrial sector.
And it might not be. We were recently reminded over on John Curl's thread of Cyril Bateman's explicitly audio-related reports on the topic (with a clue in the title of one of them, "Capacitor Sound"). I'm not sure what the "precision industrial sector" is though I take your wider point that other sectors also had an interest in confirming and quantifying what (degree-level) engineers in the audio-sector had prior dismissed out of hand.
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Old 3rd August 2012, 07:01 PM   #4755
DF96 is offline DF96  England
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Quote:
Originally Posted by Ryelands
I'm not exactly sure what you mean by "LDR non-linearity and distortion", to say "probably mainly second, so fairly harmless" is, of course, to guess, not to submit evidence.
I mean LDR voltage non-linearity i.e. an LDR is not a perfect resistor whose value is set by the light intensity. It is good, but less so than a normal resistor. This non-linearity will produce signal distortion, related to signal level. On reflection it will probably be mainly third order, rather than the second order I stated.

Quote:
The length of title bit was, as I hoped was obvious, a quip, a light-hearted dig at what I saw (since you force the issue) as Millar's heavy-handed, not to say pompous, prose. If it wasn't obvious, I apologise. That said, he made no reference to peer review, in any case a notoriously poor index of a paper's technical merit.
My remark about title length was also a quip, aimed at what I saw as possible anti-intellectualism (very common in audio); I apologise if I have jumped to conclusions. I agree that peer review is a poor guide to merit, but it is better than the absence of peer review.

My mention of a preference by some listeners for some distortion I believe arises from a comment made by James Moir in his 1961 book "High Quality Sound Reproduction", when he was reporting on published research. However, a quick look just now has failed to find the relevant section, so either I have to look harder or I saw it elsewhere. The same phenomenon, if valid, could explain some of the popularity of SE amps.

Cyril Bateman was, I believe, employed by one of the capacitor manufacturers. I note your apparently negative attitude to those who you believe may have degrees.
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Old 3rd August 2012, 08:50 PM   #4756
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Default Has anything been measured?

Has there been anything measured that explains the great sound that results from the lightspeed attenuator?

I am one of the many that have been using the lightspeed for 4+ years. It simply sounds great. If its distortion get me some more of it. It does seem strange that the addition of distortion could produce what is percieved as sonic cues normally associated with reduction in noise.

Is it simply that the resistive element in the LDR is preferable to that used in typical pots and even in the metal film resistors in stepped attenuators? Many people swear by the value of exotic resistors. Some like ecdesigns hand wind double helix wire wound resistors and swears to their superiority in i/v ciricuits.

The part that I do not understand is why I for one also percieve a not so subtle improvement in SQ when an improvement is made to the quality of the power supply to the lightspeed. One would think that with the isolation provided by the LDR that there would be no difference between a half decent linear power supply and a much better implementation with chokes and low noise discrete regulator. Yet to my ears there was a surprising improvement.
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Old 3rd August 2012, 09:54 PM   #4757
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Originally Posted by wlowes View Post
Has there been anything measured that explains the great sound that results from the lightspeed attenuator?
you will never find anything measured that results in good sound, only what results in bad soundsbut the absence of bad sound would ofcorse result in good sound
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Old 4th August 2012, 01:26 AM   #4758
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On reflection it will probably be mainly third order, rather than the second order I stated.
OK - but that's still a guess, not "evidence".


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I agree that peer review is a poor guide to merit, but it is better than the absence of peer review.
Fine, fine, fine - but what has it to to do with the topic in hand? No-one bar yourself seems interested in peer review in this context.


Quote:
My mention of a preference by some listeners for some distortion I believe arises from a comment made by James Moir in his 1961 book "High Quality Sound Reproduction", when he was reporting on published research. However, a quick look just now has failed to find the relevant section, so either I have to look harder or I saw it elsewhere.
Even if you find it (good idea to find these things before quoting them, not after), my point about the non-equivalence of the two subject populations has still to be refuted. The listening preferences of an unspecified sample of listeners using (given the date) tube amplifiers nearly sixty years ago and those of a modern population listening to different (and unarguably superior) sources using different technologies really have too little in common to help us here and even less absent detail. In other words, Moir's book has little or nothing to tell us about the Lightspeed today.


Quote:
The same phenomenon, if valid, could explain some of the popularity of SE amps.
It could at that but it's LDRs we're discussing.



Quote:
Cyril Bateman was, I believe, employed by one of the capacitor manufacturers.
Best not to patronise. At the time of writing, he'd spent 30 years designing capacitors. That's almost as long as it took me to get my degree.


Quote:
I note your apparently negative attitude to those who you believe may have degrees.
You note wrong. Ian Millar boasted that "I'm a degree-qualified engineer" (the hyphen is mine) though he didn't say which engineering discipline he was qualified in. That said, you're right - I believe he has a degree. Should I be doubting it?

My "negative attitude" is, as explained, to those who argue from authority, especially from the spurious authority of having passed an examination in something or other in one's early twenties.
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Old 7th August 2012, 06:14 AM   #4759
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Much against my better judgment I make a contribution to this thread and present this circuit...

Click the image to open in full size.

This by far a better device than a ldr attenuator.

If made with a double 5534 type op amp you can use a 1k series resistor that has considerably less thermal noise than any ldr, much less distortion and probably less 1/f noise and since the gain is continuously adjustable and always proportional to the signal level it has a virtually constant s/n ratio, it also has a log law volume control with a linear pot that is far closer to an exact log law than any log pot.
rcw
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Old 7th August 2012, 08:47 AM   #4760
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This was a thought of mine years ago, till one guru said a pot in the feedback loop is asking for trouble on wide bandwith opamps if it's not set and never turned, once on and turned all hell can break loose with dc offsets/occillations at sometimes high gain. taking out speaker/amps in a split second.

Cheers George
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