Integrated Amp discussion...

[GrimSurfer]

Then why does the Class D industry universally specify measurements with a 20KHz brick wall filter? Have you measured a Hypex amplifier without a filter, to plot the artifacts?

I don't have a problem with the use of a brick wall filter cutting off a signal outside the audible range. Nor am I a firm believer of psycho-acoustic theories that say humans can perceive well into the ultra sonic range. I do believe that the rationale of applying a brick wall filter is so that manufacturers can say, with some legitimacy, that noise is low over the amp's working range.

Of course, it helps when you limit that working range to the point so such measurements appear to work to your favour.

Is it "tricksy ", as Gollum would say? Sure. But it's a lot less tricksy than avoiding discussion or measurement of other (and far more significant) artifacts.

 

[Irvrobinson]

I don't have a problem with the use of a brick wall filter cutting off a signal outside the audible range.

I do. A brick wall filter that occurs before the power amplification stage is reasonable, as PCM audio uses, but a filter that has to exist after the power amplification stage for measurements (apparently) to look good for marketing purposes makes me suspicious. I've never seen an article that compares filtered and unfiltered measurements of a full-range Class D amplifier to highlight why the filtering is specified. If I did, and the artifacts were really innocuous, I might become an advocate. The weight and power dissipation of my ATI 3000-series amp are not attractive attributes.

 

[GrimSurfer]

I do. A brick wall filter that occurs before the power amplification stage is reasonable, as PCM audio uses, but a filter that has to exist after the power amplification stage for measurements (apparently) to look good for marketing purposes make me suspicious. I've never seen an article that compares filtered and unfiltered measurements of a full-range Class D amplifier to highlight why the filtering is specified. If I did, and the artifacts were really innocuous, I might become an advocate. The weight and power dissipation of my ATI 3000-series amp are not attractive attributes.

I'm with you on that. Good point, Irv.

 

[highfigh]

Many of these measurements require some interpretation before their significance can be fully appreciated.

A spec of 0.001% THD means less than were I to say that the distortion of an amp lies at -100dB. Things come into even sharper focus when I compare this with human hearing, which (IIRC) performs no better than -120dB detection in ideal circumstances (virgin ears, good health, high concentration, low ambient noise, lab environment).

To that we need to add the type of harmonics. Even order harmonics are part of everyday sound and are often interpreted as a normal part of the fundamental frequency being heard by the human ear. Odd order harmonics are not normal and are interpreted differently.

Now if a competing manufacturer were to say that *their* amp's THD was 0.0001%, it doesn't mean that the noise is ten times lower than the competing unit. It means that the noise is less by a very larger factor because this equates to a THD of -120dB. Not only is this -20dB better, but the nature of the decibel scale means that it has at least "half as half" as much noise.

So the difference between 0.001 and 0.0001 is like the difference between going to the moon and going to Mars. Big difference.

Now think about what this means when the THD is advertised as 0.01 or 0.1 in a tube amp. The sound might be pleasing because of the nature of the noise (even harmonics) but it is still quite noisy and well within the hearing range of retired deep sea divers and artillery officers. And that, my friends, IS noisy (though not quite as bad as the phase distortion of many loudspeakers at their crossover points).

In an earlier post, I provided a link to an EE Times article on noise measurement in Class D amps. I need to read more on the subject, but the thrust of the article is that audible non linearity is a pernicious problem inherent to Class D topologies. The author of the piece designs Class D amps, so this is not an advocacy article written by a Class A or AB designer using misdirection to avoid discussion on gain or switching noise. It's an electrical engineer talking about (what he sees as) an engineering problem.

Much gets buried (or worse, goes unmentioned) by Class D audio amp manufacturers who, with some but not unassailable legitimacy, drop a really impressive THD figures in a spec sheet.

Manufacturers throw figures around in the manner that best suits them. For a variety of reasons, few take the time to explain what those measurements mean or why they may be relevant (or irrelevant) to the consumer.

This is not a disease unique to Class D amp manufacturers, it is an industry wide problem.

It seems odd that objective measurement might need interpretation, rather than being taken literally. That tells me that the statement for the goal of that measurement needs to be clarified.

I don't know how a retired diver or artillery officer could hear such detail with the nerve damage they typically experience and I don't know how anyone, in today's environment, can have pristine hearing.

The amplifier specs that I have seen lately (by no means have I looked at everything available), involved the manufacturers trying to achieve low higher-order harmonics, to remove the more non-musical content since the first harmonic is less damaging to the program material.

It's too bad the marketing departments are able to cloud the waters, but they need to sell product, so.....

 

[GrimSurfer]

It seems odd that objective measurement might need interpretation, rather than being taken literally. That tells me that the statement for the goal of that measurement needs to be clarified.

I don't know how a retired diver or artillery officer could hear such detail with the nerve damage they typically experience and I don't know how anyone, in today's environment, can have pristine hearing.

The amplifier specs that I have seen lately (by no means have I looked at everything available),involved the manufacturers trying to achieve low higher-order harmonics, to remove the more non-musical content since the first harmonic is less damaging to the program material.

It's too bad the marketing departments are able to cloud the waters, but they need to sell product, so.....

It helps if you can accept the view that nothing is self apparent (part of the underpinnings of modern scientific thought). That makes it easier to appreciate why all measurements require some interpretation to be fully understood.

A measurement in miles per hour requires one to understand what a "mile" means and what an "hour means". It's the same thing with THD figures, but we're just not as used to dealing with them... and the industry isn't helping us to understand what they really mean. Or if they are, what little they are doing is certainly not much as the DoT helps us understand distance (mile markers) and speed (reasonably calibrated speedometers, speed warning signs, etc).

100% agree on the hearing issue. There are many occupations and past times that greatly affect hearing. Modern society isn't helping and Mother Nature can be cruel too (living in a forest filled with cicadas will fry hearing only slightly faster than living next to the ocean and being bombarded with high levels of white noise).

You are quite correct to question how anyone in today's modern and noisy society can have perfect hearing. That's one of the reasons why I believe instrumented measurement is so important.

 

[highfigh]

It helps if you can accept the view that nothing is self apparent (part of the underpinnings of modern scientific thought). That makes it easier to appreciate why all measurements require some interpretation to be fully understood.

A measurement in miles per hour requires one to understand what a "mile" means and what an "hour means". It's the same thing with THD figures, but we're just not as used to dealing with them... and the industry isn't helping us to understand what they really mean. Or if they are, what little they are doing is certainly not much as the DoT helps us understand distance (mile markers) and speed (reasonably calibrated speedometers, speed warning signs, etc).

100% agree on the hearing issue. There are many occupations and past times that greatly affect hearing. Modern society isn't helping and Mother Nature can be cruel too (living in a forest filled with cicadas will fry hearing only slightly faster than living next to the ocean and being bombarded with high levels of white noise).

You are quite correct to question how anyone in today's modern and noisy society can have perfect hearing. That's one of the reasons why I believe instrumented measurement is so important.

Measurements use units, which is to make it possible for people to understand the measurement in the first place. THD isn't a new concept WRT audio, so it should be understood better than you seem to be saying, IMO. These units aren't interchangeable but, in some cases, they can be converted for the sake of brevity or when calculations for something may demand it (E, I and R, when used to determine power, for example) or using Horsepower as the unit for work, converted from Watts. Understanding one MPH should be easy enough for everyone, but it's not- it's only an indication of the average speed but since too many people didn't pay attention, they don't really understand it. They know it as a number on their car's dash gauge but that's about all. Anyone who maintains their velocity on a curving road will get a painful reminder of the meaning of that word.

We weren't built to listen to flat frequency response audio and music- those are human inventions- our hearing is as it is in order for us to survive in the wild. If we were supposed to hear flat, I think we would have trim pots.

 

[GrimSurfer]

Measurements use units, which is to make it possible for people to understand the measurement in the first place. THD isn't a new concept WRT audio, so it should be understood better than you seem to be saying, IMO. These units aren't interchangeable but, in some cases, they can be converted for the sake of brevity or when calculations for something may demand it (E, I and R, when used to determine power, for example) or using Horsepower as the unit for work, converted from Watts. Understanding one MPH should be easy enough for everyone, but it's not- it's only an indication of the average speed but since too many people didn't pay attention, they don't really understand it. They know it as a number on their car's dash gauge but that's about all. Anyone who maintains their velocity on a curving road will get a painful reminder of the meaning of that word.

We weren't built to listen to flat frequency response audio and music- those are human inventions- our hearing is as it is in order for us to survive in the wild. If we were supposed to hear flat, I think we would have trim pots.

I agree on many of these points.

Accuracy is the goal. Flat is sometimes used loosely to say this.

I say "loosely" because it means very different things to different people. To an audio engineer, flat means unadulterated/unmodulated. To some listeners, flat can either mean lacking in dynamic range, bass, or treble etc.

There is a good case to be made for recording and having the capacity to play back sound free of extraneous artifacts. This then gives much more latitude for the listener to adjust for taste, room effects etc.

Regardless of how the listener adjusts the sound, the ears will still do what they will, including operating (more or less) according to the Fletcher-Munson curve.

So you're right... we're not supposed to hear flat. But this doesn't mean that we shouldn't ask manufacturers to deliver amps that can deliver extremely accurate sound -- or preamps (or pre-amp stages in an integrated amp) that have adequate capacity for user-specified equalization.

 

[highfigh]

I agree on many of these points.

Accuracy is the goal. Flat is sometimes used loosely to say this.

I say "loosely" because it means very different things to different people. To an audio engineer, flat means unadulterated/unmodulated. To some listeners, flat can either mean lacking in dynamic range, bass, or treble etc.

There is a good case to be made for recording and having the capacity to play back sound free of extraneous artifacts. This then gives much more latitude for the listener to adjust for taste, room effects etc.

Regardless of how the listener adjusts the sound, the ears will still do what they will, including operating (more or less) according to the Fletcher-Munson curve.

So you're right... we're not supposed to hear flat. But this doesn't mean that we shouldn't ask manufacturers to deliver amps that can deliver extremely accurate sound -- or preamps (or pre-amp stages in an integrated amp) that have adequate capacity for user-specified equalization.

I think that if THD is to be more easily understood, it should include 'First Harmonic', 'Second Harmonic', etc since a blanket statement leaves out so much info. Sure, it might be .0000000001% at some frequency, but what happens at others? We haven't even gone deeply into IM, either and I personally think that can be more important because I don't sit around listening to pure sine waves. I mean, I use them for testing, but.....

And to a musician, 'flat' means 'not to correct pitch'. Singers may not understand this concept if they rely heavily on AutoTune. I was referring to flat frequency response in light of the Fletcher-Munson et al contours.

Absolutely- we need equipment to be able to hit the mark of some kind of standards, but even now, these haven't been universally agreed to. The more we know, the more we don't know, right?

One problem that has existed since tone control and finer equalization has existed- someone always manages to use it incorrectly, to the detriment of their speakers. While the 'Happy Face' curve is technically wrong, it is fairly complementary to our perception of the audio frequency spectrum.

 

[M Code]

I'm of exactly the same view, Irv. It is about manufacturers making good choices based on what technology offers, not choosing tech and then having to apply extraordinary measures to make it work. Kind of...

Like you, I feel that AB represents a sweet spot of sorts. This is likely the result of forty years of continuous development.

Class D may get there some day, but it still has a way to go before it's ready for general amplification duty.

IMHO...
Amplifiers with a Class D output design have already made it...
Class D amplifiers already dominate the product categories for HD flat panel displays, TV soundbars, wireless audio multi-zone/source, HT subwoofers, 12V OE, 12V aftermarket, PCs, multi-media and pro-audio. The last hold-out are AVRs but there has been a few tries from Onkyo, Pioneer, Samsung, Panasonic, HK...

Just my $0.02...

 

[GrimSurfer]

IMHO...
Amplifiers with a Class D output design have already made it...
Class D amplifiers already dominate the product categories for HD flat panel displays, TV soundbars, wireless audio multi-zone/source, HT subwoofers, 12V OE, 12V aftermarket, PCs, multi-media and pro-audio. The last hold-out are AVRs but there has been a few tries from Onkyo, Pioneer, Samsung, Panasonic, HK...

Just my $0.02...

Sort of like driver design making it with the introduction of the transistor radio?

Class Ds are great for stuff where audibility is more important than fidelity. They're ok for limited applications like subs, where DSP can adjust for linearity and the frequency range is tight, I suppose. Lo-fi? Yup. Mid-fi? Maybe. Hi-fi? Nope.

So I guess the question is whether audiophiles will remain Semper Fi, or accept mid-fi until the tech improves.

 

[lovinthehd]

Sort of like driver design making it with the introduction of the transistor radio?

Class Ds are great for stuff where audibility is more important than fidelity. They're ok for limited applications like subs, where DSP can adjust for linearity and the frequency range is tight, I suppose. Lo-fi? Yup. Mid-fi? Maybe. Hi-fi? Nope.

So I guess the question is whether audiophiles will remain Semper Fi, or accept mid-fi until the tech improves.

What a bunch of nonsense. Class D is at the hi-fi stage. Lofi and midfi are stupid descriptions based on price point.

 

[PENG]

They're ok for limited applications like subs, where DSP can adjust for linearity and the frequency range is tight, I suppose. Lo-fi? Yup. Mid-fi? Maybe. Hi-fi? Nope.

So I guess the question is whether audiophiles will remain Semper Fi, or accept mid-fi until the tech improves.

I assume you are kidding..

 

[GrimSurfer]

What a bunch of nonsense. Class D is at the hi-fi stage. Lofi and midfi are stupid descriptions based on price point.

The term"hi fi" was coined in the 1950s. It was generally agreed that so-called products were capable to reproducing sound in the 50-15kHz range.

But time as moved on. Now, hi-fi is generally understood to mean systems capable of producing good quality sound across the entire human hearing range. There is much ambiguity concerning what constitutes quality sound. Regardless, the prefixes hi-, mid-, and lo- have never been based on component price. Instead, equally ambiguous terms like the detested "audiophile grade" are used to equate price to performance.

This is something I reject. Indeed, I have posted elsewhere that I cannot see any real correlation between price and performance.

Elsewhere I posted a link to an EE Times (professional electrical engineer's journal) article calling for better ways to measure distortion in Class D amps. The author, himself and engineer of Class D amplifiers, raised concerns about significant non-linearity.

Elsewhere in this thread, mention has been made of brick wall filters being used to limit frequency (and distortion) of certain Class D amps above 20kHz. I take a rather benign view of this, largely due to a general ambivalence to whatever goes on in a gain circuit outside the audible range.

Regardless, I cannot ignore the non-linearity issue inherent to Class D topologies. I can see where some manufacturers might employ DSP to help mitigate non-linearity, but I don't think the reliance of DSP is a very good sign of excellence in gain. It's a crutch.

Now the use of DSP and Class D amplifification in subwoofers is quite common -- and it clearly works. But a subwoofer is not a hi-fi device. Subwoofers only operate over a very narrow frequency band. Their levels of distortion are notoriously high -- sometimes 15% or more.

So I don't see it as a big deal to use Class D amps for subs... or for laptops, tablets, and cell phones due to these devices' limited need for high fidelity. But I, like the Class D amp engineer authoring the EE Times article, see serious issues elsewhere. These might preclude them from serious consideration in some applications.

I have no doubt that these issues WILL get resolved, just as other issues such as switching noise were resolved to a manageable level in Class AB amps. But we're not there yet.

 

[lovinthehd]

The term"hi fi" was coined in the 1950s. It was generally agreed that so-called products were capable to reproducing sound in the 50-15kHz range.

But time as moved on. Now, hi-fi is generally understood to mean systems capable of producing good quality sound across the entire human hearing range. There is much ambiguity concerning what constitutes quality sound. Regardless, the prefixes hi-, mid-, and lo- have never been based on component price. Instead, equally ambiguous terms like the detested "audiophile grade" are used to equate price to performance.

This is something I reject. Indeed, I have posted elsewhere that I cannot see any real correlation between price and performance.

Elsewhere I posted a link to an EE Times (professional electrical engineer's journal) article calling for better ways to measure distortion in Class D amps. The author, himself and engineer of Class D amplifiers, raised concerns about significant non-linearity.

Elsewhere in this thread, mention has been made of brick wall filters being used to limit frequency (and distortion) of certain Class D amps above 20kHz. I take a rather benign view of this, largely due to a general ambivalence to whatever goes on in a gain circuit outside the audible range.

Regardless, I cannot ignore the non-linearity issue inherent to Class D topologies. I can see where some manufacturers might employ DSP to help mitigate non-linearity, but I don't think the reliance of DSP is a very good sign of excellence in gain. It's a crutch.

Now the use of DSP and Class D amplifification in subwoofers is quite common -- and it clearly works. But a subwoofer is not a hi-fi device. Subwoofers only operate over a very narrow frequency band. Their levels of distortion are notoriously high -- sometimes 15% or more.

So I don't see it as a big deal to use Class D amps for subs... or for laptops, tablets, and cell phones due to these devices' limited need for high fidelity. But I, like the Class D amp engineer authoring the EE Times article, see serious issues elsewhere. These might preclude them from serious consideration in some applications.

I have no doubt that these issues WILL get resolved, just as other issues such as switching noise were resolved to a manageable level in Class AB amps. But we're not there yet.

Hi fidelity merely means what it says, of high fidelity. Not highest fidelity, just high fidelity, or faithful to the source. You can nitpick specs or post 15 year old articles, but class D is hi fidelity.

 

[Mikado463]

Hi fidelity merely means what it says, of high fidelity. Not highest fidelity, just high fidelity, or faithful to the source. You can nitpick specs or post 15 year old articles, but class D is hi fidelity.

agreed, as I pointed (post #64) to a recent listen that I had to a very nice Offering from Rogue Audio.

Come on 'Grimster' get the wax out of your ears !

 

[GrimSurfer]

Hi fidelity merely means what it says, of high fidelity. Not highest fidelity, just high fidelity, or faithful to the source. You can nitpick specs or post 15 year old articles, but class D is hi fidelity.

Agree. Where did I say "highest fidelity"?

As for faithfulness to the source, one must draw a reasonable line somewhere. Most Class A isn't high fidelity... too much noise, albeit sometimes hidden in first and second order harmonics but still there.

The vast majority of Class D isn't high fidelity unless you accept that tablets, cell phones and laptops are high fidelity devices (they aren't because they are seriously limited in frequency range and response). Those are examples of engineers wisely choosing Class D amps on the basis of their strengths for those particular applications. Ditto for powered subs.

Class D still has significant issues to overcome. Not in 15 year old applications but new ones. Frankly, I wouldn't touch a Peachtree with a ten foot pole. Sure, they're really inexpensive on a watt-per-dollar perspective. This might make them better deals for some, butthey don't measure all that well once you get past the wattage and THD. Linearity, is till an issue. Harmonics are still an issue.

There are some PS Audio products that come damned close but have you ever noticed that when PS Audio gets really serious, they use topologies other than Class D? Just sayin'.

I own several Class D amps. They work fine for what they do. But ATT, quality Class AB designs like a Bryston B60, Moon 250i, and Benchmark AHB2 (all mid priced amps) obliterates the best of the Class Ds out there at any price.

 

[M Code]

The term"hi fi" was coined in the 1950s. It was generally agreed that so-called products were capable to reproducing sound in the 50-15kHz range.

But time as moved on. Now, hi-fi is generally understood to mean systems capable of producing good quality sound across the entire human hearing range. There is much ambiguity concerning what constitutes quality sound. Regardless, the prefixes hi-, mid-, and lo- have never been based on component price. Instead, equally ambiguous terms like the detested "audiophile grade" are used to equate price to performance.

This is something I reject. Indeed, I have posted elsewhere that I cannot see any real correlation between price and performance.

Elsewhere I posted a link to an EE Times (professional electrical engineer's journal) article calling for better ways to measure distortion in Class D amps. The author, himself and engineer of Class D amplifiers, raised concerns about significant non-linearity.

Elsewhere in this thread, mention has been made of brick wall filters being used to limit frequency (and distortion) of certain Class D amps above 20kHz. I take a rather benign view of this, largely due to a general ambivalence to whatever goes on in a gain circuit outside the audible range.

Regardless, I cannot ignore the non-linearity issue inherent to Class D topologies. I can see where some manufacturers might employ DSP to help mitigate non-linearity, but I don't think the reliance of DSP is a very good sign of excellence in gain. It's a crutch.

Now the use of DSP and Class D amplifification in subwoofers is quite common -- and it clearly works. But a subwoofer is not a hi-fi device. Subwoofers only operate over a very narrow frequency band. Their levels of distortion are notoriously high -- sometimes 15% or more.

So I don't see it as a big deal to use Class D amps for subs... or for laptops, tablets, and cell phones due to these devices' limited need for high fidelity. But I, like the Class D amp engineer authoring the EE Times article, see serious issues elsewhere. These might preclude them from serious consideration in some applications.

I have no doubt that these issues WILL get resolved, just as other issues such as switching noise were resolved to a manageable level in Class AB amps. But we're not there yet.

IMHO...
Certain Class D amplifier solutions deliver superb sonics, comparable to the finest Class A-B amplifiers.. I would agree there were audible shortcomings in the earliest Class D amplifier solutions but that was 15 years and the design engineers, FET & controller device guys have made incredible improvements since then. So I guess we have to disagree about their future market penetration/success but since the market emphasizes max power, less heat, smaller footprint, higher efficiency and lower costs. So to me.. going forward in the next few years Class D amplifiers solutions will become the norm...

Just my $0.02...

 

[GrimSurfer]

IMHO...
Certain Class D amplifier solutions deliver superb sonics, comparable to the finest Class A-B amplifiers.. I would agree there were audible shortcomings in the earliest Class D amplifier solutions but that was 15 years and the design engineers, FET & controller device guys have made incredible improvements since then. So I guess we have to disagree about their future market penetration/success but since the market emphasizes max power, less heat, smaller footprint, higher efficiency and lower costs. So to me.. going forward in the next few years Class D amplifiers solutions will become the norm...

Just my $0.02...

I totally agree that the future is in Class D. There are too many benefits to overlook. Engineers have done truly exceptional work to date to iron out the bugs, but development must continue. Then, and only then, will Class D topologies be able to convincingly replace Class A and AB designs.

 

[Mikado463]

the 'future' is here ......

 

[lovinthehd]

I totally agree that the future is in Class D. There are too many benefits to overlook. Engineers have done truly exceptional work to date to iron out the bugs, but development must continue. Then, and only then, will Class D topologies be able to convincingly replace Class A and AB designs.

I think you're simply behind the times. Plenty of amps to compete with the ones you named. That they're putting class d in other devices is meaningless in this context.