 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
46.140.171.83
In Reply to: RE: So are you an absolutist? posted by Chris from Lafayette on June 14, 2024 at 11:41:34
I am pretty much an absolutist...none of my gear has negative feedback other than degenerative feedback (like a cathode follower would use...even then I am not sure I have any cathode follower circuits in my gear...maybe my phonostage...)
The problem with only using a little bit of feedback is that you still have relatively high distortion but you have created a whole bunch of high order distortion, which remains unmasked and is likely audible.
Empirically though I have found that amps with a little bit of feedback often still sound more dynamic and less "gray" tonally than those that use massive amounts.
As Geddes and others point out, you can tolerate a fairly high amount of low order (meaning primarily 2nd and 3rd order...although Cheever allows for more at higher SPL because of the ears own distortion generation acting as a mask) due to masking. In fact, if the harmonics are effectively masked, it sounds to the listener as if there is NO distortion at all.
Cheever posits that as long as the distortion components are falling below the ears own distortion pattern and intensity that the component will sound pure and undistorted...even if it has measurably high distortion compared to other components that don't sound as pure. The pattern has to match (and at a given SPL) or remain below the ears own harmonic distortion generation.
As the ear makes essentially nothing above 9th harmonic...even at very high SPL (at normal listening levels it makes nothing really above 5th harmonic), ANY distortion harmonics higher than that will be audible even at exceedingly low levels.
As to why high feedback amps can sound "dead", "gray" and lacking in perceived dyanmics, especially on high sensitivity speakers where all is revealed, I think it has a lot to do with the "noise" floor. Crowhurst demonstrated in the 1960s that high feedback makes a lot of distortion produts...essentially an infinite number with a complex music signal. These are mostly at every low levels and essentially generates a signal correlated "noise" floor. True noise is not correlated with the music signal and as such it is possible to hear below that noise floor which helps with space, dynamics and low level detail. A correlated noise floor acts as a wall that one cannot hear below and as its modulating with level, it probably has very detrimental effects on the perception of the music. This might be why a minimal amount of feedback is not so bad as it would not create a very strong effect on this signal correlated noise floor.
High feedback also means that a lot of the back EMF from the speaker will find it's way back into the signal path, as some of it is injected back to the input stage (for amps with global feedback). That signal of course looks nothing like what went into the speaker and besides it is signal that doesn't align with what is currently passing through the amp.
Finally, Nelson Pass also weighed in on feedback (although his conclusion was a bit wishy washy). You can read that here:
https://www.passlabs.com/technical_article/audio-distortion-and-feedback/
Follow Ups:
You call his conclusion "wishy washy" but I would characterize it as less dogmatic.
You know, this whole discussion started when a few posters seemed to get triggered when Amir and Audio Science Review were brought up (not by me I might add!). As I've said all along, people have the right to their beliefs and perceptions - even though these perceptions may (and do!) change from day to day (as Geddes pointed out!).
People can believe what they want but the listening data strongly suggests that there are preferences that probably don't align with some people's belief. What is clear, is that THD and IMD don't correlate well with those preferences.
he doesn't bother following links to actually understand what's being discussed.
I found the listening correlation data comparing THD, IMD and G m compelling. You might as well flip a coin with the first. And really enjoy the selection chosen!
You're trying to pretend that all I care about is THD. Once again, not true.
you don't pay attention. You don't follow links. You don't follow observations. You don't even read the manuals for your gear.
Let's review what my last post observed of your behavior:
"As previously observed, he doesn't bother following links to actually understand what's being discussed."
It is clear from other questions you've made that you didn't download and read the two references found a day earlier here.
Hint: blue text in my posts signals a hyperlink. Click Chris, click!
I'm convinced this will be the very first time you've seen the referenced Powerpoint slides like this:
. . . studies which have only the most peripheral relationship to to my posts. Let me remind you of what the main point of my posts was: that measurements (and NOT just THD!) can help us in describing the sound of a given component. You admitted that that was true yourself. But then you turned around and started in with a bunch of bunk you somehow divined from my previous posts.
So I don't follow observations? I think that's MORE true of you. If distortion measurements are so useless, why do almost ALL audio manufacturers provide them? Are they trying to deceive customers? Seems to me that you and Morricab are out in the cold with you own contentions on this point. (And, BTW, I'm NOT disputing that masking is a thing. After all, I prefer to listen to Dolby Atmos these days - which I listen to mostly via Apple Music's LOSSY streaming! Talk about masking! LOL!)
And just because you posted a picture of your listening environment which CLEARLY showed your speakers placed perpendicularly to each other doesn't make it incumbent on me to follow YOUR observations - or anyone else's "observations" for that matter.
which CLEARLY showed your speakers placed perpendicularly to each other.
How they radiate into the room, however, is symmetric. Per the manual, each is aimed 30 degrees to listening area.
I can recommend a good oculist for you. ;)
Indeed. Cheever also came up with a metric that included SPL because the ear/brain masking extent (i.e. what harmonics and how much) changes with SPL.
This is why low SPL is more critical than high SPL because masking is less effective, particularly for high order harmonics even at very low levels. They also tend to be about the same regardless of amp output in a feedback type amplifier. It is also probably why low level resolution and soundstage/imaging are most affected by the negative effects of high order distortion and negative feedback.
. . . was that even INDIVIDUAL subjective perceptions of sound can change from day to day or even hour to hour FOR THE SAME PERSON perceiving the same sound.
How are you going to account for that - and then "quantify" it? It seems to me that the only option you have is to do so in a faux scientific way - by arbitrarily assigning "values" to reactions which cannot by their nature be quantified.
The two of you try to denigrate listeners who set some store by measurements (and not just THD!), and yet you then turn around and quote these "scientific" study measurements which are IMHO pretty dubious.
You clearly haven't heard of statistics...think about it or read about it and it will perhaps come to you eventually how you can get some useful data out of individual preferences.
As to the industry, they provide the measurements they kind of have to, not the ones that would be useful (if fitted with the proper model). They publish THD and maybe IMD...almost no one provides a detailed FFT and model fitting. Aries Cerat provides the level of H2 and H3 at a given power...but that is an exception rather than the rule and the assumption they make is that there is an exponential decay in the harmonics with increasing harmonic order.
. . . that equipment can have as much distortion as possible, and you would still claim there's no correlation? I think one appeal vinyl has for some listeners is that vinyl distortion is euphonic - and they find that pleasing. Euphonic does not equal accurate.
Where do you draw the line? How much distortion is acceptable. Is it anything goes? I doubt that many listeners would agree you in that case.
There is audible and then there is perceived as distorted.
Look at some of the levels of distortion applied in the Geddes paper. Some are very low and some are pretty darn high.
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]