Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 479 - AVS | Home Theater Discussions And Reviews
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post #14341 of 14354 Old Today, 02:48 PM
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IME, over EQ'ing can cause a lot of distortion.

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post #14342 of 14354 Old Today, 03:20 PM
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Quote:
Originally Posted by LastButNotLeast View Post
Was that Jim referring to <30Hz as "extremely low bass"?
Here?
Below 30hz includes 10hz you know

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Originally Posted by artur9 View Post
I think what's missing is how does one address distortion? Where does it come from?

For the other measurements there's almost a one-to-one problem to fix path. Bad ETC -> tame reflections, bad waterfall -> absorption, distortion -> ???
The speaker usually. Over driving an amp maybe. In the bass region, if objects are rattling or shaking, this can show up as distortion.

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Originally Posted by artur9 View Post
Jim's a music guy, not a movie bass head like you.

Unless - pipe organ?
Big Pipe Organs have a fundamental at 16hz. That is low from any point of view. But most of the music I listen to doesnt have much below 30hz. HT is a different animal certainly.

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Originally Posted by Alan P View Post
IME, over EQ'ing can cause a lot of distortion.
EQing in null regions particularly.

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post #14343 of 14354 Unread Today, 04:38 PM
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Originally Posted by AustinJerry View Post
Measuring is simple. Interpreting what various levels of distortion mean is somewhat more complex. That is why I have not include the topic in the Guide for now.
Thank you for that. The guide was really helpful in bringing me up to speed on the basics behind finding reflections with the ETC and understanding ringing with the waterfalls. Perhaps a few example graphs, one showing little distortion and one showing significant distortion, along with some basic commentary could do the trick.

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Originally Posted by jim19611961 View Post
In many ways, IMO, its easier than many other subjects. Lower is always better. In the graphs provided here and others ive seen, THD levels in the 0.2% -0.5% range were typical for the mid range and treble, and 1-3% in the bass region for typical listening levels. Perhaps 5-6% for extremely low bass (<30hz). If your within these numbers, I would say your fine. Double these levels is suspect, triple or more and there is a problem somewhere.
Maybe it is obvious - I have to look at the graphs again, but when I looked at them for the first time I couldn't quite tell what was low and high vs THD vs ? etc.

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Originally Posted by artur9 View Post
I think what's missing is how does one address distortion? Where does it come from?

For the other measurements there's almost a one-to-one problem to fix path. Bad ETC -> tame reflections, bad waterfall -> absorption, distortion -> ???
I was wondering the same thing. The few follow up posts helped explain it. So as long as speakers are good quality and EQ is not messed up and amps are in good shape and not over driven and there's not room noise then little distortion should show up. I think I got it. Now I just need to understand how to spot it in the graphs.
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post #14344 of 14354 Unread Today, 04:56 PM
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Originally Posted by 3ll3d00d View Post
The fix is changing the speaker and/or adding more subs and/or changing the way you have them eq'ed
Bingo. I had a boost at 20Hz. When I discovered distortion was > 10%, I reduced the boost (and, I think, moved it to 25Hz). Lots of distortion can't be good for the drivers, either, I would think.

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Quote:
Originally Posted by LastButNotLeast View Post
Bingo. I had a boost at 20Hz. When I discovered distortion was > 10%, I reduced the boost (and, I think, moved it to 25Hz). Lots of distortion can't be good for the drivers, either, I would think.
I know its generally considered a no-no to boost the dips. However is there a rule of thumb for when it is ok to apply a little gain, and under what circumstances (and how much)?
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post #14346 of 14354 Unread Today, 05:19 PM
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The "rule of thumb" is that it's never a good idea. It is, however, sometimes a necessary evil. You can boost a dip, you just can't boost a NULL. So if you apply a boost and nothing happens, you may as well un-apply it, since it's not doing any good, and probably doing some harm.

You're overthinking (one of my favorite passtimes) distortion. REW has a nice help file:



This is one of my graphs. Notice the THD at 20Hz:



This is another. Notice more THD at 20Hz (less desirable):



Interestingly, on either of those, if you go to the null at 70ishHz, you can see the distortion go up. So I certainly don't want to try to add any boost there.

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I just noticed the crosshairs don't show up on the capture. Click somewhere on your graph and you can drag the crosshair around to read the THD at that point.

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post #14347 of 14354 Unread Today, 05:56 PM
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Originally Posted by LastButNotLeast View Post
The "rule of thumb" is that it's never a good idea. It is, however, sometimes a necessary evil.
Like when? And is looking at the distortion a good way to know whether the trade off was worth it (and if so, what thresholds do you use to judge that)?

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You can boost a dip, you just can't boost a NULL.
Right. But at what point does a dip become a null, because isn't a null essentially just a very large dip? Is a -20dB dip a null, a -40dB dip a null etc?

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So if you apply a boost and nothing happens, you may as well un-apply it, since it's not doing any good, and probably doing some harm.
Makes total sense. Of course there are times then boosting a dip can looks smooth, but without realizing what one may have done as far as clipping or distortion. Which is why I asked about determining the effectiveness of such a boost above.

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You're overthinking (one of my favorite passtimes) distortion.
This is AVS. That's what we do around here eh?

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REW has a nice help file:
Yes I looked at that yesterday, but I was unsure of what it was referring to. And I just looked again - its pretty technical and not sinking in, yet.

Quote:
This is one of my graphs. Notice the THD at 20Hz:
Nothing really sticks out at 20Hz, at least compared to what's to the left of it. Unless that's distortion too at 10 Hz and 15 Hz.

Quote:
This is another. Notice more THD at 20Hz (less desirable):
Now this hump at 20 Hz is much more notable. What is the scale for the THD? I don't think its dB on the left, and on the right it just shows a label of 200 Hz at the bottom of the axis. When looking at the THD, where do you draw the line between an acceptable and unacceptable amount/level?

Quote:
Interestingly, on either of those, if you go to the null at 70ishHz, you can see the distortion go up. So I certainly don't want to try to add any boost there.
Yes I see it go up at 70Hz. However it does so just a tiny bit, when compared to the large hump at 20 Hz. So why is this movement at 70 Hz noteworthy?
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post #14348 of 14354 Unread Today, 06:15 PM
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Quote:
Originally Posted by lovingdvd View Post
Right. But at what point does a dip become a null, because isn't a null essentially just a very large dip? Is a -20dB dip a null, a -40dB dip a null etc?
A null is a very special thing. It's where the output from your speakers are destructively interfering with itself. Because of that no amount of boost will fix it because it will always destructively interfere with itself.

You can move where a null is by moving your speakers or by using more of them.
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post #14349 of 14354 Unread Today, 06:25 PM
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I had multiple equipment failures last week. One of them was my L/R subwoofers' amp. Since I had to re-optimize any way I took the opportunity to put in my 2x4 MiniDSP as a 1x4 LFE splitter and EQ system. Hats off and thanks to AustinJerry for another invaluable guide on how to do so.

The end result is here. I can't play that loudly until the amp comes back so please forgive the low level on this graph. But I think it shows that I need to work a little more on the splice between the subs and the main speaker? Or could that dip have another explanation?

I ended up with 3 (4) peak PEQ filters in the DSP. One to kill a mode at around 28Hz, one to apply probably too much boost around 72Hz and I don't recall the last one or two.

I'll have to redo it all again when the sub amp returns from its "vacation". Overall I'm pleased. Should I be? No smoothing, no EQ other than the aforementioned. Sounds good to me, quite a bit more clarity than previously and the bass line on Ella Fitzgerald's Fascinating Rhythm sounds very clean to me.

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post #14350 of 14354 Unread Today, 06:42 PM
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Like when? And is looking at the distortion a good way to know whether the trade off was worth it (and if so, what thresholds do you use to judge that)?
As mentioned earlier (jim? I don't remember, but it was many pages back), some distortion at deep bass is acceptable (and probably unavoidable). We can probably agree that anything over 10% is probably "too much." Above your crossover (and probably a good bit below it), you can probably have a THD < 1%. Please notice the excessive use of "probably." There don't seem to be any hard and fast rules for this.

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Right. But at what point does a dip become a null, because isn't a null essentially just a very large dip? Is a -20dB dip a null, a -40dB dip a null etc?
No, as artur explained.

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Makes total sense. Of course there are times then boosting a dip can looks smooth, but without realizing what one may have done as far as clipping or distortion. Which is why I asked about determining the effectiveness of such a boost above.
That's why it's nice to be able to check that area on a distortion graph.

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And we do it WELL!

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Yes I looked at that yesterday, but I was unsure of what it was referring to. And I just looked again - its pretty technical and not sinking in, yet.
Play with your own graphs and it will start to make (some) sense.

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Nothing really sticks out at 20Hz, at least compared to what's to the left of it. Unless that's distortion too at 10 Hz and 15 Hz.
You may have missed my edit about the cursor/crosshairs. Doing this on your own graphs will make more sense. Click and drag the cursor and see what happens to the THD.

Quote:
Now this hump at 20 Hz is much more notable. What is the scale for the THD? I don't think its dB on the left, and on the right it just shows a label of 200 Hz at the bottom of the axis. When looking at the THD, where do you draw the line between an acceptable and unacceptable amount/level?
I don't think there's a "scale"; it's just a percentage (signal to noise? good vs. evil? I have no idea, but lower is better).

Quote:
Yes I see it go up at 70Hz. However it does so just a tiny bit, when compared to the large hump at 20 Hz. So why is this movement at 70 Hz noteworthy?
Though the "hump" isn't much, the readings as you move the cursor over that area change dramatically. It is noteworthy in that it is at the same place as the dip, which means it's probably a null, and not correctable with eq.

Michael

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post #14351 of 14354 Unread Today, 06:43 PM
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Originally Posted by artur9 View Post
You can move where a null is by moving your speakers or by using more of them.
Speakers, not nulls.

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post #14352 of 14354 Unread Today, 06:52 PM
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Quote:
Originally Posted by artur9 View Post
I had multiple equipment failures last week. One of them was my L/R subwoofers' amp. Since I had to re-optimize any way I took the opportunity to put in my 2x4 MiniDSP as a 1x4 LFE splitter and EQ system. Hats off and thanks to AustinJerry for another invaluable guide on how to do so.
As they say on all the police shows, "I'm very sorry for your loss."

Quote:
The end result is here. I can't play that loudly until the amp comes back so please forgive the low level on this graph. But I think it shows that I need to work a little more on the splice between the subs and the main speaker? Or could that dip have another explanation?
Run left and subs and right and subs. If they both look good, then it's the interaction between the left and right. Try moving them, toeing them in, facing them out, etc.

Quote:
I ended up with 3 (4) peak PEQ filters in the DSP. One to kill a mode at around 28Hz, one to apply probably too much boost around 72Hz and I don't recall the last one or two.
Huh? Still a bit of a peak there. I, personally, would flatten that peak completely and raise the overall level of output of the subs.

Quote:
I'll have to redo it all again when the sub amp returns from its "vacation". Overall I'm pleased. Should I be? No smoothing, no EQ other than the aforementioned. Sounds good to me, quite a bit more clarity than previously and the bass line on Ella Fitzgerald's Fascinating Rhythm sounds very clean to me.
But is there any distortion?
If you like the sound, you're heading in the right direction. You can always save your settings and continue to experiment. As a matter of fact, I'm getting the impression that it never ends.

Michael

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post #14353 of 14354 Unread Today, 07:20 PM
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Originally Posted by LastButNotLeast View Post
As they say on all the police shows, "I'm very sorry for your loss."
Thanks. Losing my pre pro was quite a blow.

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Huh? Still a bit of a peak there. I, personally, would flatten that peak completely and raise the overall level of output of the subs.
You should see it without the cut! I just got tired of fighting it since I know it's a temporary situation in any case. As each sub is brought in the frequency, cut and Q changes according to the minidsp's EQ tab. I got tired of chasing it.
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But is there any distortion?
For you, I checked. Highest distortion is about 9% at 15Hz. Mind you, my subwoofers are an 8" and 3 10" subs. I'm surprised they can even go that low in the aggregate.
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If you like the sound, you're heading in the right direction. You can always save your settings and continue to experiment. As a matter of fact, I'm getting the impression that it never ends.

Michael
Never ending is right. I was so looking at getting a Rythmik 12SE to replace the 8" sub because it is by far the least musical of my subs. But someone up there (or down there) had other plans.
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post #14354 of 14354 Unread Today, 07:31 PM
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Originally Posted by Alan P View Post
^^^

Sounds about right.
Okay. Thanks...
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