So what is deep negative feedback and how is it influencing sound?

[voodooless]

That’s so true! Soon after, he promoted a purely analog-designed amplifier, claiming its sound was better than that of amplifiers with more scientific designs.

Can we please name and shame these individuals? None of this makes any sense. 99.9% of amps are fully analog designs. “More analog” doesn’t make it less scientific…

 

[solderdude]

That’s so true! Soon after, he promoted a purely analog-designed amplifier, claiming its sound was better than that of amplifiers with more scientific designs.

That's the whole issue...

An amp can perform technically worse but 'sound' more pleasant to some people.
The sound quality arguably has not increased but the perception of the 'tester' has changed or the gain was higher or the output resistance was higher which can result in a different tonality.
No or little feedback can result in a higher output resistance. The effect of which depends on the speaker impedance/amp output resistance ratio (Damping Factor).

So... yes an amp with worse technical performance can be preferred by people BUT the sound quality has not improved (arguably) but the perceived sound may be more pleasant to the user.

Now the final arbiter is what people hear and like... but for engineers the signal fidelity is what counts.
Signal fidelity does have some but not 100% relation to perceived sound quality unless the 'distortion' (linear or non-linear) is so bad in which case we can call the design 'broken'.

 

[sergeauckland]

Nelson Pass isn't the only designer that is (was) perfectly able to design good quality amplifiers, but preferred technically flawed designs. The late and seldom lamented Richard Dunn was another. His Tresham amplifiers were superb, but then went on to manufacture amplifiers with no protection, and requiring high inductance loudspeaker cables to maintain stability.

I get the impression that designing technically flawed amplifiers provides the excuse for a 'story' behind the design that attracts a certain type of 'audiophile' who trusts their ears rather than measurements. If it's audibly flawed, even better, as the difference in quality is always better.

S.

 

[Jim Taylor]

I get the impression that designing technically flawed amplifiers provides the excuse for a 'story' behind the design that attracts a certain type of 'audiophile' who trusts their ears rather than measurements.

Scientists trust data over their ego.
Denialists trust their ego over data.
Businesses can easily manipulate ego. Manipulating data is not quite as easy.

 

[Multicore]

Specifically, at what frequency does it affect sound? For example, 1 MHz?

Can we really talk about 1MHz sound? An acoustic signal, yes, but unless there's an animal that can hear it, is that signal a sound?

Asking for a friend.

 

[NTK]

How to design and build "blameless amplifiers" is not a secret, and has not been for decades. Competent engineers and manufacturers do it routinely, which effectively makes high enough performance audio amplifiers a commodity.

All these talks by "gurus" are just their attempts at product marketing differentiation, aimed at the gullible who always consider products normies believe good enough are below them, as they have the "golden ears", "knowledge", "taste", money, and the willingness to spend it.

 

[JiiPee]

Can we really talk about 1MHz sound? An acoustic signal, yes, but unless there's an animal that can hear it, is that signal a sound?

Asking for a friend.

Technically, as long as it is a mechanical wave (as opposed to electromagnetic wave), it is still classified as a sound wave. There are ultrasonic sound waves that no animal can hear as far as we know.

 

[solderdude]

Can we really talk about 1MHz sound? An acoustic signal, yes, but unless there's an animal that can hear it, is that signal a sound?

Asking for a friend.

There are actually transducers that have 'mechanical' vibrations (and can pick those up) in the 1-22MHz range.
Used for medical echo's.
The air is too 'thick' for those to be able travel through air (hence the stuff they put on the skin) so are not audible but they do exist.

Still waiting for the first audiophile to put one on top of their speakers and claim a super-duper tweeter able to reach 20Mhz and make all kinds of claims.

 

[Axo1989]

Can we please name and shame these individuals? None of this makes any sense. 99.9% of amps are fully analog designs. “More analog” doesn’t make it less scientific…

Yes it’s odd reading this thread without knowing who/what the OP is referring to.

 

[DNCAgain]

My statement was incorrect, I apologize.

In fact, his description is completely the opposite. The advantages he claimed are as follows:

1. Pure digital design (no need for digital-to-analog conversion);
2. Feedback-free design;
3. GaN material (provides greater thrust);
4. PCM to PWM framework.

However, he did not show any data except for labeling the power as 500W×2!

Yes it’s odd reading this thread without knowing who/what the OP is referring to.

 

[solderdude]

PCM to PWM is conversion from digital to PWM.
This can be without overall feedback.
GaN is handy when combining high switching speeds with high current and voltages.

 

[DVDdoug]

Hopefully the PWM is filtered to analog. It's simply a low-pass filter. It will work without a filter because the speaker is a low-pass filter but only cheap class-D amps are made without a filter.

I've never seen a thrust spec for an amplifier.

 

[voodooless]

Hopefully the PWM is filtered to analog. It's simply a low-pass filter. It will work without a filter because the speaker is a low-pass filter but only cheap class-D amps are made without a filter.

The main issue here is EMC compatibility. Special encoding schemes are needed to not need an output filter, and even then you usually only see it on low-power amps.

My statement was incorrect, I apologize.

In fact, his description is completely the opposite. The advantages he claimed are as follows:

1. Pure digital design (no need for digital-to-analog conversion);
2. Feedback-free design;
3. GaN material (provides greater thrust);
4. PCM to PWM framework.

However, he did not show any data except for labeling the power as 500W×2!

These kinds of designs exist, but I’m sure most wil use some kind of feedback, or have performance issues. And GaN isn’t a miracle cure. While efficiency is very good, it hasn’t been proven to provide objectively better audio performance. What particular design are we talking about?

 

[Barrelhouse Solly]

I've done some audio restoration as a hobby. One thing that is a common tool in all restoration software is negative feedback. You record a noise sample from the material you're trying to repair and the software applies it 180 degrees out of phase to the program material. You have to work with the intensity but for things like record hiss it does a decent job. The danger is that it can reduce the information content when the noise is in a frequency range where the "good" program material is similar to the noise.

 

[MaxwellsEq]

I recently came across a viewpoint on a video website that companies like Topping use "deep negative feedback" in their products, which makes their THD (Total Harmonic Distortion) data look more impressive but leads to a "smearing" effect (loss of details) and a loss of dynamics.

However, given that he once had a dispute with Topping, it's hard to judge the accuracy of this claim.

Below is another discussion from the same video website about amplifier.


“Since common integrated operational amplifiers have a very narrow open-loop bandwidth (a few hertz to several kilohertz), they are often used in amplifiers with deep loop negative feedback applied to extend the passband. However, this approach inevitably introduces severe transient intermodulation distortion (TIM), degrading the sound quality. Therefore, amplifiers built with integrated op-amps, while capable of achieving good steady-state performance through deep negative feedback, cannot be considered high-fidelity (Hi-Fi) from a transient perspective.”

To answer your questions correctly, you need to have a bit of the basics of control theory. At first glance, it's all quite obvious. Once you get into it a bit deeper, the mathematics can seem a bit heavy, but is essential for designing stable systems when the bounds are challenging (e.g. when rates of change are large).

There's nothing in the theory that says control systems are bad. Quite the opposite, since a system without controls may have runaway characteristics leading to damage to the system or the person operating it! However, the control system needs to have the same level of requisite complexity as the system it controls.

There's absolutely nothing in the theory that would justify anybody making a claim that the feedback or feedforward loop makes things sound worse. Any engineer attempting to make such a claim should back it up with proper mathematical analysis.

https://people.bath.ac.uk/lcol20/itt10/2019_06_10_guiver_control.pdf

 

[TurtlePaul]

There's absolutely nothing in the theory that would justify anybody making a claim that the feedback or feedforward loop makes things sound worse. Any engineer attempting to make such a claim should back it up with proper mathematical analysis.

That is not quite true - you make too strong of a statement. The chart of feedback level vs. harmonic distortion has already been posted.

In designs with <20 dB of negative feedback, the result is a reduction in overall distortion but the mechanism is to trade second harmonic, which is the name note on octave up, for third harmonic and higher order harmonics.

This isn’t an issue for the Topping amps which are using 100 dB+ of negative feedback, but you can make amps sound worse by tuning the feedback to maximize third the fifth harmonic.

 

[Labhound]

Negative feedback also has the benefit of increasing an amplifiers damping factor which (from my limited understanding) better controls the speaker cone movement.

 

[Tell]

1. Pure digital design (no need for digital-to-analog conversion);

When the source is digital it's physically impossible to listen to it without a DAC, and in this case is the amplifier itself that's the DAC when it converts the signal to PWM and then filtered by the amp/speakers to get a smooth analog AC voltage for your speakers to reproduce.

 

[Multicore]

There are actually transducers that have 'mechanical' vibrations (and can pick those up) in the 1-22MHz range.
Used for medical echo's.

Yes. My friend feels that calling such vibrations sounds is a bit of a stretch. She suggested "ultrasonic sound" is a contradiction in terms as it means sound beyond sound. Ultrasonic vibration, ultrasonic waves, ultrasonic acoustic signals are all good but ultrasonic sound?

 

[FrantzM]

To answer your questions correctly, you need to have a bit of the basics of control theory. At first glance, it's all quite obvious. Once you get into it a bit deeper, the mathematics can seem a bit heavy, but is essential for designing stable systems when the bounds are challenging (e.g. when rates of change are large).

There's nothing in the theory that says control systems are bad. Quite the opposite, since a system without controls may have runaway characteristics leading to damage to the system or the person operating it! However, the control system needs to have the same level of requisite complexity as the system it controls.

There's absolutely nothing in the theory that would justify anybody making a claim that the feedback or feedforward loop makes things sound worse. Any engineer attempting to make such a claim should back it up with proper mathematical analysis.

https://people.bath.ac.uk/lcol20/itt10/2019_06_10_guiver_control.pdf

There should exist an emoji for: THANK YOU!!!!!!
Also the link deserves from me. Another
THANK YOU