ernestcarl
Major Contributor
It seems to fit the context well -- though, eh, it may entirely be incidental.
Hopefully, someone in the know can confirm.
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What is group delay?
- Thread starter KTN46
- Start date
It seems to fit the context well -- though, eh, it may entirely be incidental.
Hopefully, someone in the know can confirm.
Well, reading this thread, I'm tempted to wonder: is there anyone here who really knows what he/she is talking about? And - is the group delay relevant/audible...? It would be great if someone could point to a song or upload test tones that have the potential to show group delay in a system....It seems to fit the context well -- though, eh, it may entirely be incidental.
ernestcarl
Major Contributor
No need for an ABX trial here. With enough all pass filters, a difference should be easily audible. It is entirely possible that you will like the track with more group delay because the bass will sound somewhat artificially louder -- diminishing nuance and clarity in the rest of the spectrum.
I used Neumann's kick drum test track from their subwoofer test signals package which can be downloaded on their website.
Attachments
The difference is tremendous. The sample without GD sounds much more defined. I guess that now I would need to invite a drummer with a kick drum to my living room and compare its sound to what comes out of my speakers
. I am wondering what speakers are "good" and what speakers are "bad" regarding GD? The two samples you uploaded were artificially modified. Are there really speaker on the market that make a kick drum sound that smeared..?
Thanks to all of you since my first post for offering clear, understandable and helpful explanations for a lay person like me—sincerely.
ernestcarl
Major Contributor
The difference is tremendous. The sample without GD sounds much more defined. I guess that now I would need to invite a drummer with a kick drum to my living room and compare its sound to what comes out of my speakers
Oh, yes... I've seen some multi-ways with a lot of GD...
An ASR member's subwoofer GD:
May be. If you have never been exposed to the formula for a line in grade school or whatever (or have forgotten over the course of time) then understanding the concept may be difficult. I was trying to be reasonably concise so it may take a couple of readings to follow. I assumed most folk were familiar with the concept of linearity, a linear function for a straight line, and how a function that is not linear can create distortion. Group delay tells us if the phase is linear over frequency or instead it changes, creating distortion. In the time domain the distortion appears as smearing of the signal edges (rise and fall).Seriously? Maybe you missed the tone of my post?
Apparently not.
A straight line of y = mx with m = 1 looks like the blue line below. If I make the slope (m) depend upon the input (x) we get the orange line, which is no longer perfectly straight. The next plot shows the error. This is what happens when group delay is not constant, the (phase) line is no longer straight.
Now try with some signals, in this case the first five frequencies in a square wave. The amplitudes decrease as frequency goes up (see https://www.audiosciencereview.com/.../composition-of-a-square-wave-important.1921/). Notice how all nine signals line up in the middle and again at the end.
If all the signals arrive at the same time, that is group delay is constant, then this is what you see when you add them all up:
A perfect square wave has frequencies out to infinity, and this is just five, so it does not have perfectly sharp (straight) edges and the top and bottom are not perfectly flat. It is perfectly symmetric, however, with edges and top and bottom the same across the entire period.
Now adjust the group delay so it is not constant but instead each successively higher frequency is shifted just a little bit more. Notice how the signals no longer align perfectly in the middle and at the end but are spread out a bit:
The output when we sum them all looks different and is no longer symmetric:
We can see the difference more clearly by showing them both on the same plot:
Hopefully this helps visualize how group delay can impact the signal, and why constant group delay is a typical design goal.
Still doesn't necessarily say if I know what I am talking (writing) about... - Don
Sir, I’m a physician and epidemiologist, I understand linearity. I’ll do as you suggested and try to read it through more than once, although there surely must be some way to explain the basics of how group delay translates to an audible result that doesn’t require this level of esoterica and detail.
I did not mean to single you out personally. I just think that some folks on here are like myself—hobbyists seeking fundamentals that will allow them to interpret measurements in practical terms. And I’ve learned can incalculable amount of useful info from the many generous, patient folks on here who are eager to teach.
However this particular thread seemed to be a bit of a grandstanding exercise, a show of academic oneupmanship on the part of some highly didactic folks who were not paying attention to the struggles of others involved. The question was basic; the explanation dove right into the deep end before some folks learned to swim.
Well, now there's even more grandstanding, as I combined the posts and added a thread to the reference section containing the info I presented. Sorry... I am not sure what else to do to make it clearer, any suggestions? - DonSir, I’m a physician and epidemiologist, I understand linearity. I’ll do as you suggested and try to read it through more than once, although there surely must be some way to explain the basics of how group delay translates to an audible result that doesn’t require this level of esoterica and detail.
I did not mean to single you out personally. I just think that some folks on here are like myself—hobbyists seeking fundamentals that will allow them to interpret measurements in practical terms. And I’ve learned can incalculable amount of useful info from the many generous, patient folks on here who are eager to teach.
However this particular thread seemed to be a bit of a grandstanding exercise, a show of academic oneupmanship on the part of some highly didactic folks who were not paying attention to the struggles of others involved. The question was basic; the explanation dove right into the deep end before some folks learned to swim.
I get it Jim, and I assure you that I didn’t list credentials to be ostentatious or to condescend—in truth I felt a bit condescended to by the insinuation that I might lack the wattage to understand the subject at hand. You’re right that this may be a very difficult concept to teach—it’s just that I’m not sure teaching was the intention of the folks who chimed in.I'm not a physician and I'm not an epidemiologist. I'm over 70 y.o., and I'm as dumb as a box of rocks. When information is presented on this forum and I don't understand it, I burn up the bandwidth with searches on Google, and I try to learn.
Learning isn't always easy. Sometimes there just aren't simple, easy-to-understand answers to complex problems. But if I never try, I'll never succeed.
I might be naive, but I think that's true for everyone.
Jim
The truth is that if you read the entirety of this thread, the OP asked a simple question—asked for help basically—and he was met with the most arcane, technically and mathematically complex answers, despite his repeated pleas for a more simple explanation. I followed along experiencing the same struggle, and got increasingly impatient with the pursuant debate over the most granular minutiae of this concept.
Eventually I began to suspect that none of the participants knew how to explain it cogently, which is perfectly fine—if their motives are to try to be helpful, not to be intellectually superior.
Group delay is part of the routine tests performed during Amir’s measurements. Understanding the fundamentals of what it indicates allows the less experienced members of the forum to feel capable and included in the discussions that follow the review.
There’s a whole bunch of folks on here who are professionals in the audio field, and I could never hope to achieve their grasp of these subjects. I’m grateful that they’re here to help me, and they always do with utmost patience and respect. I don’t think any of them participated in this discussion, and I wish they had—I might have walked away from this feeling the satisfaction of learning something new, instead of the defeat of feeling intimidated.
There are plenty of forums here suited to delving into high-level inquiry into audio engineering concepts. Hopefully in the future when someone else asks for help understanding something, which I think takes bravery and humility, those at an intellectual advantage will be more sensitive and attentive to the feedback from their audience. That’s what would help me anyway. Take care!
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To @Jim Taylor and @srkbear do you understand this diagram?
Odd harmonics of a 1000 Hz square wave (Note: Square waves are comprised of only odd order harmonics.)
Do you understand what is basically occurring in this diagram/giff?
I ask because to understand anything previous to this you need to understand what is occurring in these two diagrams/giffs.
Odd harmonics of a 1000 Hz square wave (Note: Square waves are comprised of only odd order harmonics.)
Do you understand what is basically occurring in this diagram/giff?
I ask because to understand anything previous to this you need to understand what is occurring in these two diagrams/giffs.
I did not read most of the posts. I usually browse when a test is running or something else is going on and I have a bit of "free" time; rarely is ASR my primary focus. My bad. I have no way of knowing the technical level of people posting, but do tend to assume basic math and geometry knowledge, which is not always true especially since the last time someone looked at it may have been in grade school. At one time I could produce a periodic table (last page of second inorganic chem class was a blank table to fill out) and even spout about 30 steps of the Krebs cycle.; couldn't even start that now. Posting here is a minefield; there are people with almost zero math background, and designers and experts with decades of experience. Trying to explain concepts to such a wide audience is a challenge, and clearly it is easy to do as I did and overshoot the mark.
Group delay is simple equation but may take a year's worth of courses or more to understand the terms and what it means. And several paragraphs and an hour or two of work to try to explain it in a manner that makes sense to someone with no background in the field. Hopefully the posts help, but it is hard over the 'net to explain to someone who just says "I don't understand" without them digging just a little to help explain what they don't understand. I tried to explain with words and then with pictures but it needs a better teacher and smarter guy than I...
I took a shot, missed, sorry - Don
Group delay is simple equation but may take a year's worth of courses or more to understand the terms and what it means. And several paragraphs and an hour or two of work to try to explain it in a manner that makes sense to someone with no background in the field. Hopefully the posts help, but it is hard over the 'net to explain to someone who just says "I don't understand" without them digging just a little to help explain what they don't understand. I tried to explain with words and then with pictures but it needs a better teacher and smarter guy than I...
I took a shot, missed, sorry - Don
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ernestcarl
Major Contributor
BTW, I don’t really think one has to truly understand the fundamental inner details of every single thing explained to get the gist of the concepts.
I use EQ and FIR filters all the time and it’s not like I have attained a “God” PhD level of understanding, nor grasp every single variable and step in the equations involved. I’ve said it more than once in this forum and elsewhere that I’m (almost completely) utterly hopeless when it comes to math.
However, it’s going to be even more difficult when there’s nothing tangible one can relate of these ideas in the real world — e.g. any example/issue you’re trying to resolve or mitigate.
As for me, I’ve stopped worrying about at which point time variance becomes a real audible issue, and simply try to reduce it wherever I can in the chain e.g. crossovers and EQ, room positioning and acoustic treatment. I’ve even overdamped the cabinet and blocked some of my speakers’ bass reflex ports partly to reduce GD.
I use EQ and FIR filters all the time and it’s not like I have attained a “God” PhD level of understanding, nor grasp every single variable and step in the equations involved. I’ve said it more than once in this forum and elsewhere that I’m (almost completely) utterly hopeless when it comes to math.
However, it’s going to be even more difficult when there’s nothing tangible one can relate of these ideas in the real world — e.g. any example/issue you’re trying to resolve or mitigate.
As for me, I’ve stopped worrying about at which point time variance becomes a real audible issue, and simply try to reduce it wherever I can in the chain e.g. crossovers and EQ, room positioning and acoustic treatment. I’ve even overdamped the cabinet and blocked some of my speakers’ bass reflex ports partly to reduce GD.
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This video explains a sine wave function, how they add and subtract and then how a square wave is made. The math is there but the important part here is to understand how the sine waves combine to create square waves.
ernestcarl
Major Contributor
Whoah! The ending line there in the animated presentation sounds a little bit too philosophical for comfort.
Simply and shortly - group delay tells the signal time delay of the circuit in the pass band. Below shown in the example of the 5th order active low pass filter. Here, group delay of the LPF with 17kHz corner is about 20us.
I don't hear a lot of difference, not with my speakers in near-field (LS50), and not with headphones (Bose QC35 II Bluetoorh).
danadam
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Same here. In attachment I put them in a single file: 2x original, 2x group delay, 2x original, 2x group delay.
Scary stuff...lol. I was a little wide eyed too.Whoah! The ending line there in the animated presentation sounds a little bit too philosophical for comfort.
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