Can Someone Please Explain "Hearing A Volume Control"?

Davey · « **Reply #20 on:** 13 Jul 2012, 01:52 am »

Quote from: Early B. on 13 Jul 2012, 12:52 am

Let me get this straight -- you're saying that LDR-based volume controls appear to sound better due to increased distortion???? Wow -- I didn't know more distortion sounds better than less distortion. I had it backwards.

Well, I'll assume you're not being sarcastic, but yep, welcome to the world of high-end audio where higher distortion can sound better.

Vacuum tube amplifier manufacturers have known for years that increased levels of distortion....of the proper type....can make things sound really good. These might be devices that perform horribly on the test bench with high levels of even-order distortion, yet they sound just fine.

Our ears/brain is an amazing audio processor.

Cheers,

Dave.

Early B. · « **Reply #21 on:** 13 Jul 2012, 02:05 am »

Quote from: Davey on 13 Jul 2012, 01:52 am

Well, I'll assume you're not being sarcastic, but yep, welcome to the world of high-end audio where higher distortion can sound better.

Vacuum tube amplifier manufacturers have known for years that increased levels of distortion....of the proper type....can make things sound really good. These might be devices that perform horribly on the test bench with high levels of even-order distortion, yet they sound just fine.

Our ears/brain is an amazing audio processor.

Cheers,

Dave.

OK, so LDRs create increased even order distortion similar to vacuum tubes, so that's what makes them sound better?

*Scotty* · « **Reply #22 on:** 13 Jul 2012, 03:19 am »

Actually nothing has been posted here documenting how much and what kind of distortion that LDRs have.
For that you will have to wade through many pages of posts on the DIY audio forum.
None other than Nelson Pass measured an LDR and posted the amount of distortion it had which raised a big ruckus over there with the person who was promoting them. They may sound better to some people in some systems due to their basic simplicity. Less is more.
Scotty

*Scotty* · « **Reply #23 on:** 13 Jul 2012, 03:35 am »

There I knew I could find it if I bothered to look for it. Here is the distortion plot at 1 volt in, most CD players put out 2volts. The distortion is primarily 3rd harmonic according to Nelson.

Nelson Pass's comments from diy Audio "Lastly, here are the distortion figures I got with a constant 1 volt input to the attenuator. More input voltage naturally results in
greater distortion, except at the -6 dB value, where the 3rd harmonic
distortion of the two LDRs cancels. From -1 to -6 dB, the distortion
is compressive, and from -6 to -40 dB the distortion is expansive.
Here is a link to the complete thread.
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp-134.html#post1520950
Scotty

Occam · « **Reply #24 on:** 13 Jul 2012, 04:25 am »

Quote from: *Scotty* on 13 Jul 2012, 01:18 am

Everything is relative. If you have replaced a piece of crap with a LDR based attenuator you may hear an improvement. Likewise if you replace an inferior preamp with an optocoupler with a buffered output you may hear an improvement.
However if you have a minimalist buffer/preamp as I do these things are counter-indicated.
In my case my preamp has 5 parts in the signal path, one of them is a 15 amp pass transistor.The rest of the parts are passive and include a DACT attenuator at the front of the circuit. The preamp/buffer will pass a 1MHz square-wave perfectly from input to output and even cleans up the leading edge of the square-wave because it will drive the input of the oscilloscope better than the output of signal generator. This indicates that the device has at least a 10MHz bandwidth as it will pass the 1MHz square-wave in an unaltered form. The THD+noise is 0.002% for 2 volts output.
It would be the height of folly to put something with more circuit complexity and an inferior power supply in place of the DACT attenuator and expect a superior outcome.
No thank-you.
Scotty

Dang Scotty - You're sounding like a certain enthusiastic newbie, but at least you've actiually heard at least one of the attenuators compared. Have you heard a well implemented LDR attenuator in your own system? To dogmatically dismiss them based solely upon an article of faith surprises me.

JohnR · « **Reply #25 on:** 13 Jul 2012, 04:30 am »

What's the "article of faith"?

Occam · « **Reply #26 on:** 13 Jul 2012, 04:45 am »

Quote from: JohnR on 13 Jul 2012, 04:30 am

What's the "article of faith"?

That the objective metric,THD, negatively correlates to the subjective measure of sound quality.

*Scotty* · « **Reply #27 on:** 13 Jul 2012, 05:10 am »

Nobody has sent me one yet. And apparently in its best implementation you basically have an LDR with some kind of buffer after it? So now we have a preamp shootout, which is a little different than a simple substitution of one type of pot for another. I would certainly listen to an example if one was sent to me.
I think the the basic LDR without bells and whistles appears to have a bent transfer function. I also confess to just not being all that interested in tackling another project, with the concomitant investment in time and money. That's longhand for cheap and lazy.
Scotty

Rclark · « **Reply #28 on:** 13 Jul 2012, 05:12 am »

Scotty I will send you my Opto to try out as soon as I get my new rig in Sept, if you like.

I've heard about this distortion, which is strange, being as it's just light, because so far it has been the clearest and purest, clear as a bell.

DaveC113 · « **Reply #29 on:** 13 Jul 2012, 05:14 am »

Quote from: Occam on 13 Jul 2012, 04:45 am

That the objective metric,THD, negatively correlates to the subjective measure of sound quality.

I agree about keeping an open mind, but it also seems like you're adding a lot of 3rd order distortion with the LDR, which is rarely subjectively pleasing. You can't build and experiment with everything... I rejected trying it based on several other factors as well. I could definitely be wrong, and it could be much better than a resistor based attenuator, but it's likely I'll never know.

lol, Scotty beat me to "cheap and lazy"... true here as well

*Scotty* · « **Reply #30 on:** 13 Jul 2012, 05:18 am »

I think the corollary might be true. Low THD does not always correlate with perceived sound quality. I would go so far as to say that higher THD and IM is not your friend and I wouldn't go out of my way to choose unheard, a part with intrinsically more distortion.
Scotty

*Scotty* · « **Reply #31 on:** 13 Jul 2012, 05:48 am »

RClark, that's the problem, it's not just light. There is electricity on either end of the beam of light and a part with a non-linear transfer function. What is missing in action on the Warpspeed is a distortion curve plotting voltage in versus attenuation. This would tell you how much and what kind distortion has been added by the LDR. A properly chosen chip buffer following the LDR won't add enough distortion to talk about.
And none of the above will tell you how much damage has been done to the signal by the insertion of the DUT in-between your source and your power amp. Only listening to it in your own system will reveal what's happening.
In my system a preamp other than my own has quite a job to do. I am feeding two stereo power amplfiers and two plate subwoofer amplifiers and the shortest set of IC's is 21ft. long.
The point is everyones system presents a different load to a "guest" component, occasionally an incoming component may be incompatible with the system it is partnered with purely due to loading considerations. This where the YMMV disclaimer comes into play.
Scotty

Rclark · « **Reply #32 on:** 13 Jul 2012, 05:51 am »

Well, if you want to test it, I'd love to send it to you, as soon as I have something else I can use. I absolutely adore mine with my maggies, and any replacement has big shoes to fill as far as I'm concerned.

*Scotty* · « **Reply #33 on:** 13 Jul 2012, 06:14 am »

I would be more interested in how it sounds in my system than how it measures on the bench at this point.
I'll listen to it when you get around sending it.
Scotty

Rclark · « **Reply #34 on:** 13 Jul 2012, 06:16 am »

Ok, it'll be a while, but I'll be in touch. You will have to shorten up your system a bit, obviously, unplug some things. Don't think it will drive those long cables.

Early B. · « **Reply #35 on:** 13 Jul 2012, 01:17 pm »

Some of you guys are passing judgment on LDR attenuators based on a single spec, which we all know tells you almost nothing about how it sounds. I've owned several active preamps, a Placette RVC, and a Promitheus TVC. The Warpspeed blows all of them away in every conceivable category. The thread is about "hearing a volume control," not measuring one. With the Warpspeed, my ears don't hear less distortion relative to the other preamps I've owned. Whether the measurements prove otherwise is irrelevant.

Davey · « **Reply #36 on:** 13 Jul 2012, 02:27 pm »

Quote from: Early B. on 13 Jul 2012, 01:17 pm

With the Warpspeed, my ears don't hear less distortion relative to the other preamps I've owned. Whether the measurements prove otherwise is irrelevant.

Of course. But why the sarcasm then if someone points out the increased distortion levels might be responsible for the sound of an LDR volume control? If you want your volume control to impart a sound to your sound, there's nothing wrong with that.

Some of us are just more interested in the "why" of things. That's okay, isn't it?

Cheers,

Dave.

DaveC113 · « **Reply #37 on:** 13 Jul 2012, 04:14 pm »

Quote from: Early B. on 13 Jul 2012, 01:17 pm

Some of you guys are passing judgment on LDR attenuators based on a single spec, which we all know tells you almost nothing about how it sounds. I've owned several active preamps, a Placette RVC, and a Promitheus TVC. The Warpspeed blows all of them away in every conceivable category. The thread is about "hearing a volume control," not measuring one. With the Warpspeed, my ears don't hear less distortion relative to the other preamps I've owned. Whether the measurements prove otherwise is irrelevant.

Actually, it's because:

1. It is sensitive to heat, should have own chassis
2. Requires buffer
3. Requires power supply
4. Better units become fairly complicated
5. Questionable value for money
6. And last but not least, added distortion, which I only learned about yesterday....
7. I almost forgot cheap and lazy.

It may be true that we can't correlate every single measurement to the way it sounds, but it is possible to characterize the difference in sound with 3rd order distortion.

InfernoSTi · « **Reply #38 on:** 14 Jul 2012, 01:01 am »

Quote from: InfernoSTi on 12 Jul 2012, 01:29 pm

I found the clarity and dynamics were an immediate improvement over volume pots. I wouldn't go back at this point...although I think if I had to, I would go the stepped attenuator route with high quality resistors.

I should have said "over STANDARD volume pots" regarding the improved sound. I have also bolded the rest of my earlier statement which is my other choice would be a stepped attenuator. I would use RPR resistors which I like very much.

My interest was in adding to the discussion of "can you hear a volume control" not defending/attacking the merits of any one choice. In the end, I would hope that those who have an opinion about a particular device would post their opinions based on their actual experience, not on what they have read somewhere or what they extrapolate from limited data. I, for example, don't post on the merits of particular type of phono cartridge because I don't have first hand knowledge of such. And it certainly would be foolish of me to quote particular specs and state unilaterally that phono cartridges would all sound bad because they all suffer a particular type of spec liability. In fact, I would do the opposite...I would seek to learn what it is that those who use them find so alluring and attracting.

I hope that the conversation refocuses on what people have actually experienced (good or bad) so that we all may learn something useful.

Best,
John

Davey · « **Reply #39 on:** 14 Jul 2012, 01:53 am »

Why is it always (in audio especially) that folks can't comment on topics without firsthand experience?

I've never been in Congress, but I can't offer an opinion on the job my Congressman is doing?

We can't learn something useful from a poster about Device X unless it's been in his system and he's actually listened to it?

My goodness.

Dave.