Audio Distortion and THD Explained
soundguys.com
soundguys.com
> Measured THD doesn’t appear to correlate particularly with our reviewers’ subjective impressions. > It is rare to find commercially available headphones where harmonic distortion is even an issue worth drawing attention to.
Turns out most listeners can't tell or aren't bothered as long as the quality is good-enough.
- people who can "hear" different ethernet cables to their system. Audiophile ethernet switches. - endless wittering about jitter, despite nobody ever getting a measurement of jitter in a system newer than about 1985 that would possibly be audible.
I'm not sure where most of it comes from other than some unscrupulous operators making devices that "solve" your jitter or ethernet issues with nonsense products that can't possibly work in the way the manufacturer describes.
It has made most of the forums worthless as sources of decent information about hi-fi. Any suggestion that the worries about jitter or digital cables (or even good old RCA cables) cannot possibly affect what you are hearing are shouted down by hordes of screaming jitter monkeys. Something of a shame if you were a beginner and wanted some concrete information about what you should be looking for in a hi-fi.
Guys (I have never encountered a female audiophile of the "fancy cables and magic pens" variety) like talking about gear. Many hobbies have forums in which microscopic details of expensive products get scrutinized. Bikes, cameras, cars, outdoor gear, knives. Audiophilia is the same.
It certainly used to be the case in the valve era that results were extremely variable. It is still the case that speaker construction matters a lot. But now, in 2021? At the kind of volumes you might reasonably want in your house, pretty much any class D amplifier that has been competently constructed will do the job really well. You need reasonable efforts to avoid PSU noise and accidentally amplifying EMI and that's it. You can get high-quality DACs on a single chip for about $10. https://www.mouser.co.uk/c/?marcom=110885714
That creates a serious problem for hobbyists: there's no longer a barrier to entry! There's no longer an expensive climb up to the higher echelons. What do you do when the gate you were keeping has been bypassed by the affordable electronics barbarians? You have to retreat to a more esoteric ivory tower.
It seems to get worse the more money the posters have (maybe because salesmen get to sell them more weird speakers), and also if they're British they start talking about special power cables and something called PRAT.
Headphone reviews often seem to have incorrect claims about "speed" and "effortlessness", although I think those might actually describe something, just not what they think it is.
It may also be related to why people want to "do the research" and discover things like their own homegrown immunization protocol, rather than just going and getting a vaccine.
I just always find it interesting. No customer has ever asked me for the plot of distortion products vs freq for a loudspeaker in pro-audio. Or the metallurgic compositions of the tinsel wires.
Digital isn't perfect but compared to what an analogue playback system does, it might as well be considered as such. It gave them nothing to write about when a $120 disc player could reproduce audio as well as a $2000 player. They seemed to have doubled and tripled down on the nonsense ever since.
Not sure why audiophiles fall for it, other than the general "tweakiness" aspect of some audio enthusiasts who are always looking for the next thing to spend their money on. It's tough to have a hobby when if you buy the gear, you have little to complain about until it's made obsolete.
I'm on the opposite side of finding it interesting though. There is a lot of "your ears aren't good enough" dog piling going on to shout down any doubts about cables and whatnot.
Not denying that there is a lot of hogwash to go along as well...
That element probably ends up being some sort of counterbalancing social force to unbridled gadget consumption whose end product is $3000 cables.
Maybe the problem is nothing they make can compare to used Stax electrostatics.
I think there's a social custom in the community, that relates to "you can be your own expert." That is, opinions are weighted by some function other than technical knowledge and expertise, such as status as a musician, enthusiasm, cost of equipment owned, etc. Nobody wants to come out and say: "You're imagining things." Technical discussions often erupt into flame wars.
And there are some areas where things are probably measurably different, and it boils down to taste, but the measurements are hard to do. I can hear differences between the two instruments that I own. Does that mean I'm bonkers?
At the same time, engineers who aren't immersed in this field tend to be polarized into two extremes: Some are audiophiles. Others simply dismiss everything as audiophile nonsense.
In my typical setup, I try and work as a stage hand, and let normal FOH and monitor engineers work with the products, where I can observe all the issues that crop up. That way I can get clean feedback from band members, and production staff without, being tainted by association with the brand.
They are all shiny toys, but care surprisingly little about acoustics — a field that is known to have the highest impact on any listening environment. Then you have to realize you are human. I hear the same mix differently, when I listen to it for a second time without a break inbetween. I listen to it differently at any time of the day, depending on the mood, if I ate, depending on the weather. And I need to know these differences in perception because I have to deal with them when mixing.
Isn't the end goal of Hifi to listen to music in a way you can enjoy? Of course looks and how a setup "feels" makes a difference there, but I got the feeling many audiophiles are beyond enjoying music. I guess there is a reason why they are 99% male
"The Z-5500 will consistently give you great sound on a daily basis and was tested by THX experts as well as our audio team."
"The Logitech Z-5500 is the best all-around PC speaker system we have used to date."
etc. This thing sports 10% THD and sounds like ass (or cheap boombox) when compared to run of the mill home system amplifier from the eighties/nineties (those were usually 0.1-0.9%).
https://www.jstage.jst.go.jp/article/ast/26/1/26_1_50/_pdf Table 1 sums it up pretty nicely. Just for some reference cheapest clock crystals have jitter measured in single digit picoseconds, with PLLs somewhere in low teens.
In real systems, for example a video call, there is one clock for the microphone ADC, one clock for the video frame rate, one clock for the sender's computer, one clock for the receivers computer, one clock for the receivers screen refresh rate, one clock in the receivers DAC, etc.
Whenever these clocks drift slightly (or a lot), most software will try to compensate by stretching or compressing the audio waveform (check logs for 'audio 67 us ahead, adjusting').
Such an effect is very noticeable in some cases. The main one being if you're doing a voice/audio call to someone in the next room and you can hear them both directly and via the call. If they sing, you can hear the result going in phase and out of phase seemingly at random.
You get the same if you hit play on the same MP3 on a Mac and a windows PC at the exact same time. While the on-screen timers never visibly drift, there are enough millisecond level drifts to really notice. Doesn't happen with two Mac's.
An introductory talk is http://www.gedlee.com/Papers/The%20Perception%20of%20Distort...
Is the real expert on both linear and non-linear distortion. The link contains links to all of his papers that are available freely.
End result is that linear distortion isn't much of a problem (we tend to ignore it), but non-linear distortion is a major issue.
https://www.soundguys.com/what-is-dither-23700/
Basically you add noise to reduce noise. Fascinating...
Monty did a pair of great videos on digital audio, including this:
for a video demonstration: https://youtu.be/cIQ9IXSUzuM?t=873