Master Thread: Are measurements Everything or Nothing?

[BDWoody]

I just merged another thread that was another flavor of the same discussion.

 

[fpitas]

Deja vu, all over again.

 

[Deleted member 21219]

I just merged another thread that was another flavor of the same discussion.

Y'know, I used to like you!

Jim

 

[tmtomh]

When discussing the audibility of distortion, we have to keep in mind that the distortion products are not a separate signal. If they were, and as low as many amps are capable of, they would be easily masked. Distortion is different in that its a modifier. IOW it changes the sound of musical instruments by adding harmonics. Harmonics define that sound of a musical instrument, in case their role isn't clear... ask any luthier about that.

For the record, I did not say the ear is super-sensitive! To many things it is not. What I did say is that its keenly sensitive to the higher orders.


A 3rd harmonic in loudspeakers is well-known to mask higher ordered harmonics. I'd be interested in a study that shows that somehow this phenomena does not happen in amplifiers as well

Has a version of Distort been issued that allows one to model rising distortion with frequency? The author mentioned on this site that he had a version that could do that but didn't release it because the idea was 'too arcane' (paraphrasing). Since this is a common problem with most amplifiers employing feedback (which is most amplifiers in general) an audibility test that does not include this behavior is oranges and apples.

If you've not read it, Bruno Putzeys has a great article on feedback:
https://linearaudio.net/sites/linearaudio.net/files/volume1bp.pdf
If you read this article you'll see how important this aspect of distortion can be. We see that, as frequency rises, when the circuit meets its Gain Bandwidth Product limit, feedback decreases on a 6dB slope so distortion rises on a similar slope. As frequency continues to increase, its not uncommon for the distortion to rise at an even faster rate than that (because the feedback can fall off on an even faster rate depending on circuit variables).

If we take the example of 1KHz as a turnover point, we can see that at 7KHz the distortion can be quite a lot higher than the THD otherwise suggests! Our ears, as pointed out earlier, will assign a tonality to this and 7KHz is at the upper end of our ear's most sensitive range. In a nut shell if Distort does not model this you can't rely on the result.

If distortion rises with frequency, I think you'll find that the THD figure that an amplifier might have in practice isn't really accurate. IMO it really isn't a useful spec.

Thanks for your reply.

Harmonics of course define the sound of a musical instrument - to the extent those harmonics are audible. Which is a key part of the question when it comes to orders of harmonic distortion, yes? What is the amplitude of an instruments's harmonics relative to its fundamental, and how does the amplitude of the instrument's harmonics compare with the amplitude of an amplifier's harmonic distortion?

I understand that for a significant portion of the audible range of frequencies, higher harmonics of those frequencies will be in quite sensitive ranges of human hearing. But I'm not sure your turnover point example of 1kHz makes a lot of sense in conjunction with Bruno Putzeys' discussion of feedback, since my reading of the performance measurements of the amp modules designed by Bruno (or in the case of the Hypex NCx and Nilai, inspired by his original designs) is that their distortion remains minimal throughout the audible spectrum, and when it does become more elevated within that still low-level range, it happens up above 5kHz or higher, where most harmonics, and all of the higher-order harmonics, are beyond the audible spectrum.

So for me the question is not whether your claims about feedback at higher frequencies, the audibility of higher orders of harmonic distortion, and so on are true - I assume you are correct. For me, rather, the question is whether your claims actually result in audible effects, since it would appear that with properly designed amps the distortion products are all extremely low; the feedback doesn't taper off as soon as your example states; and the higher order harmonics of distortion where feedback is lower are above 20kHz.

 

[Cbdb2]

Consider the fact that a good variety of analog studio effects were designed well before DSP came on the scene, including compressors / expanders, including ones built on tubes. The idea that engineers couldn't figure out how to design specific, similar effects in amps on purpose is pretty strange.

I'm not saying they did that in this case, but it's way beyond possible to do so. Fancy analog compressor / expanders existed decades ago

Compressor/expanders use a RMS signal to control a multipler and need attack and release times. You can use asome tubes as the multipler (variable mu) by changing the grid voltage, but making it input level and freq dependent on purpose needs extra circuitry (eq/rms detector) as do the attack release times which cause huge distortion if wrong. (too fast compression will amplitude modulate/flatten peaks, too slow causes pumping, both very audible). How does one do this in a simple SET amp on purpose?
A tube compressor has at least twice the circuitry as a tube amp.

 

[Ricardus]

I guess you do not know a much of mastering process? It's nothing but effects.

Is it? I don't consider compression an "effect." It is a process. Maybe this is a semantic thing but no mastering engineers I know use that word unless they are referring to things like reverb, chorus, delay, etc...

 

[Deleted member 21219]

As for me, I always clearly state that what I'm hearing is my personal impression; one is free to consider it or dismiss it as one sees fit.

Once spoken, personal impressions become a matter of opinion. As such, they have entered the domain of public review, as in assent or dissent. The assertion that they are personal does not make them unassailable.

Once you say something in public, you have a choice: defend it or admit you may be wrong.

I've done both.

Jim

 

[Cbdb2]

Not really but I am a cynic by nature. I also enjoy experimenting and tinkering (as a hobby I design and build my own amplifiers, loudspeakers, and guitar pedals for example). I try things and listen. Sometimes I am surprised by what I hear, often times I am not. I did not expect a change in power supply to make a noticeable audible difference because we shouldn't if everything is in clean DC. Maybe the wall wart I got wasn't great. Who knows. It's just one empirical observation (2 if you include my friend's P50).

Since I have 3 systems in my home, I have ordered 2 WiiM Pro Plus that are scheduled to arrive in India on September 15th and 30th (via 2 different friends). I will connect these 2 with the same linear power supply (I have 2 5V DC / 1A linear power supplies and can easily build a third) I have and check.

Blind check?

 

[kemmler3D]

How does one do this in a simple SET amp on purpose?
A tube compressor has at least twice the circuitry as a tube amp.

That, I don't know, I don't have any real electronics knowledge. But since the attack / release would be fixed in an amp, presumably it's a simpler circuit? Really no idea tho.

The effect may have just shown up by accident, I don't dispute that. The fact that it may be euphonic I guess, just a happy accident.

 

[Cbdb2]

That, I don't know, I don't have any real electronics knowledge. But since the attack / release would be fixed in an amp, presumably it's a simpler circuit? Really no idea tho.

The effect may have just shown up by accident, I don't dispute that. The fact that it may be euphonic I guess, just a happy accident.

Time constants of amps should be very short compared to the signal. A very fast compression flattens the peaks (might be the cause of some of the huge distortion in lower freqs. in that amp). I just finished DIYing an IC compressor. The rms detector and multiplier came in a THAT IC ( its an updated DBX vca). Heres the rest of a compressor, including the control circuitry, which all compressors have (even if you cant adjust them) . Attack, decay, threshold, ratio, and gain are all there and all have audible effects.
https://thatcorp.com/wp-content/upl...r-with-Variable-Attack-and-Reilease-r0A.1.pdf

I don't know how much experience with compression you have but setting one up properly is usually not trivial and very program dependent. They are actualy often used to create distortion in the studio by adjusting these settings including attack and decay. The way I see it that Amp is a bad effects box with incosistant results depending on the music. You may call it lucky, but Im sure there's better ways to get euphonic distortion if you want it.

 

[atmasphere]

Compressor/expanders use a RMS signal to control a multipler and need attack and release times. You can use asome tubes as the multipler (variable mu) by changing the grid voltage, but making it input level and freq dependent on purpose needs extra circuitry (eq/rms detector) as do the attack release times which cause huge distortion if wrong. (too fast compression will amplitude modulate/flatten peaks, too slow causes pumping, both very audible). How does one do this in a simple SET amp on purpose?
A tube compressor has at least twice the circuitry as a tube amp.

Topology plays a role in the kind of distortion the circuit will express.

For example, an SET expresses a quadratic non-linearity, so has a fairly obvious 2nd harmonic, and if designed properly, succeeding harmonics will fall off on an exponential slope. You don't have to do anything other than design a 'competent' SET and you'll get your 2nd harmonic.

Sunn 'took advantage' (on purpose or happenstance....) of this fact with one of their early solidi state guitar amps back in the late 1960s by designing a zero feedback single-ended preamp and power amp driver section; only going to push-pull at the output via a driver transformer. Despite being solid state this amp was known among guitarists for many years as one on the smoother sounding solid state guitar amps made.

Because topology has this influence, the competent designer should be able to predict the kind of distortion that will be present.

 

[kemmler3D]

The way I see it that Amp is a bad effects box with incosistant results depending on the music. You may call it lucky, but Im sure there's better ways to get euphonic distortion if you want it.

Agree...

I have a good deal of experience with compressors, (using, not building) and it's certainly true there is no one-size fits all setting. I went through a lot of drama with engineers at my previous job putting the wrong compressor settings in on a portable speaker in an effort to protect the power supply.

That said, what GXAlan measured looked more like dynamic EQ or even an expander to me, which if you just wanted to emphasize transients, would be a bit less program dependent. But again, no idea whether it was an intentional effect or what.

 

[audiofooled]

what we notice (perceptually) and recall (categorically) can't be considered as unweighted/verified data.

Yup. This light read may be just enough to put things into perspective. I find it fascinating how brain is able to process so many bits of information from sensory input, also mechanisms which are acting subconsciously to filter the data, thus making life easier and perhaps more energy efficient (information processing requires energy). But there's also unconscious bias we always seem to develop due to so much data compression. Perception plays an essential role in our day to day lives, but your may differ from mine, so a moot point when it comes to objective evaluation if no proper controls are involved.

We lkie to tnhik taht the way we laren how to raed is one ltteer at a tmie but trehe is atcullay mcuh mroe hpapnenig bhenid the crtunias.

 

[Axo1989]

It's not just in audio, I think this applies to many spheres of life. There are people who believe what they want to believe, and there are people who want to be correct more than they want to believe something. I think it takes a lot of discipline to apply the latter POV in even one area of life, let alone all of them.

Definitely. And I'm sure I gloss over things in some spheres. But I don't have much choice personally, it's almost a compulsion to want the facts behind the story. I'm suspicious of charisma, generalisations and narrative. I enjoy paradoxes and contradictions. That's been my nature as long as I can remember (career-limiting in soma contexts). I'm sure that's not unfamiliar to many here.

Some say it's butyric acid. That most North American chocolate was originally made with rancid milk, and that the manufacturers these days add butyric acid (giving the taste of vomit) on purpose. Either to get a longer shelf life, or because people demand the flavour. Other say that butyric acid is no longer found in North American chocolate, but it's just terrible quality in a number of other ways.

Either way, IMO, it give a funny link to the mechanisms of nostalgia and/or "burn-in" and how it defines our ideas of quality.

I wonder how many North Americans, who have lived in Belgium or Switzerland, still prefer their native variety of chocolate.

Bizarre, I must read up about that. But about cultural/preferential "burn-in" for sure. People can be particular enough to prefer one brand's flavour over another (Coke vs Pepsi is an obvious one, for me as a child it was tinned spaghetti). On the chocolate front, fortunately my parents took us to Europe a few years before we lived in the US (using Lindt as the base of the food pyramid almost gave me diabetes). But also we accumulate those long-term sensory memories that are surprisingly resilient. I think actual sense-perception is blended with some aspects of brand narrative or even just unrelated (ie visual) aesthetic as well as emotions associated with place and time.

One of our German Au Pairs went on and on about how much better German candy was. Then her Dad sent her a care package of her favorite stuff and it was full of Mars and Cadbury products.

(I lived in Switzerland, you don't have to convince me there is better stuff than Hershey's, but the market is very global now).

Not impossible that they are formulated slightly differently in different regions, but see above re sense-memories and associations.

 

[Blumlein 88]

Yup. This light read may be just enough to put things into perspective. I find it fascinating how brain is able to process so many bits of information from sensory input, also mechanisms which are acting subconsciously to filter the data, thus making life easier and perhaps more energy efficient (information processing requires energy). But there's also unconscious bias we always seem to develop due to so much data compression. Perception plays an essential role in our day to day lives, but your may differ from mine, so a moot point when it comes to objective evaluation if no proper controls are involved.

We lkie to tnhik taht the way we laren how to raed is one ltteer at a tmie but trehe is atcullay mcuh mroe hpapnenig bhenid the crtunias.

Yes. I'd read about the rate of information in detail in the early 1990's. Much of the stuff known had been known for some time prior to that. As shown in that link of yours senses take in about 11 mbps. Interestingly 10 mbps of that is for vision. Wonder why we are more prone to be biased by what we see, and why tests of our senses need to be "blinded". All of this is filtered down so we can work at about 50 bps rates.

A common experience I've found interesting. Going into some place with drinks in those paper cups with a lid. You order tea and get Coke or vice versa. You have an expectation of what that first sip is. What you experience in taste when you've been given the wrong drink is not the taste of Coke when you expected tea. It isn't tea you taste and it isn't the normal Coke taste because of what you expected. Only the 2nd sip tastes like Coke normally tastes to you.

 

[YSC]

I guess you do not know a much of mastering process? It's nothing but effects. Effect after effect, quite subtle though. Final touch. Emotion. Technically quite advanced of course, if you referring that.

Adding effects to the mix is one thing but using a pre defined effects box to start your judgement of what to add is another thing to begin with

 

[YSC]

By hearing? You still have your senses, beside calculations? That is the biggest mistake by mixer or mastering engineer to trust just numbers and hope the best.

Hearing from what? A headphone and speaker? A neutral one which is “not right” or a well designed by hearing phone or speaker? But the “well designed by hearing” one already add their effects so that they “sound right” in a neutral source, and further adding effects will throw off the balance…

Thing is you design something for high transparency, you can’t tune it further by hearing except for hearing obvious artefacts. It’s like cooking, you can’t add a certain recipe about the amount of salt added of yours to make every raw material Taste better, let alone design the recipe from a seasoned raw meat to begin with

 

[Axo1989]

Yup. This light read may be just enough to put things into perspective. I find it fascinating how brain is able to process so many bits of information from sensory input, also mechanisms which are acting subconsciously to filter the data, thus making life easier and perhaps more energy efficient (information processing requires energy). But there's also unconscious bias we always seem to develop due to so much data compression. Perception plays an essential role in our day to day lives, but your may differ from mine, so a moot point when it comes to objective evaluation if no proper controls are involved.

We lkie to tnhik taht the way we laren how to raed is one ltteer at a tmie but trehe is atcullay mcuh mroe hpapnenig bhenid the crtunias.

Yes, fascinating to consider sensory input, bandwidth and processing speed.

If we are ok with analogies to our silicon friends, I would not limit my conceptual model to foreground processing and necessary data compression, but also consider multiple threads and background processing. I think it's an oversimplification to divide conscious/unconscious with a hard boundary. We may have something more like a conscious/subconscious/unconscious continuum.

I expect we process conceptual thinking and kinesthetic awareness differently, for example, and we can certainly learn the latter as well as the former. With practice, we don't need to put the latter into mental words or even word-pictures (maybe we do with initial learning) so that data rate (or data transform) bottleneck isn't applicable. Kinesthetics may still be subject to direction/intention, just without mental language processing.

We can also practice cognitive therapies and expand the boundary of the conscious into the subconscious. Maybe similar with emotional intelligence, awareness of sense-perceptions and so on. Not my field specifically so I'll have to think about it some more.

 

[audiofooled]

Yes, fascinating to consider sensory input, bandwidth and processing speed.

If we are ok with analogies to our silicon friends, I would not limit my conceptual model to foreground processing and necessary data compression, but also consider multiple threads and background processing. I think it's an oversimplification to divide conscious/unconscious with a hard boundary. We may have something more like a conscious/subconscious/unconscious continuum.

I expect we process conceptual thinking and kinesthetic awareness differently, for example, and we can certainly learn the latter as well as the former. With practice, we don't need to put the latter into mental words or even word-pictures (maybe we do with initial learning) so that data rate (or data transform) bottleneck isn't applicable. Kinesthetics may still be subject to direction/intention, just without mental language processing.

We can also practice cognitive therapies and expand the boundary of the conscious into the subconscious. Maybe similar with emotional intelligence, awareness of sense-perceptions and so on. Not my field specifically so I'll have to think about it some more.

Perhaps our quantization process is susceptible to errors as well and loss of accuracy in general.

 

[Gorgonzola]

You said earlier: However the fact remains the many people can hear differences between amp 'A' and amp 'B'. You state it as a fact. It is an unsupported fact.

Sorry for any semantic imprecision. The fact I'm talking about is the testimony of people who insist they can that they can hear differences, not whether those differences are actually real. If you doubt what people attest to I can recommend a couple of audiophile sites. (Personally I'm convinced that often the differences actually are real.)