Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 445 - AVS | Home Theater Discussions And Reviews
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post #13321 of 13348 Old 01-23-2015, 12:47 PM
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Originally Posted by tvuong View Post
Here it is. Please let me know what you find. Thanks in advance.

https://www.dropbox.com/s/n7mkd7hde4...0hot.mdat?dl=0
An mdat of the entire frequency range (10-20K) or so?

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post #13322 of 13348 Old 01-23-2015, 01:24 PM
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^^ that was just 7-250hz subs only. Do you want to have the speaker(s) and subs from 10-20k? If so, center and subs, left and subs, right and subs are good? Or you like to have left plus right and subs also? Thanks.
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post #13323 of 13348 Old 01-23-2015, 01:29 PM
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Originally Posted by tvuong View Post
^^ that was just 7-250hz subs only. Do you want to have the speaker(s) and subs from 10-20k? If so, center and subs, left and subs, right and subs are good? Or you like to have left plus right and subs also? Thanks.
Left OR Right with subs.

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post #13324 of 13348 Old 01-23-2015, 01:36 PM
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Originally Posted by 3ll3d00d View Post
^
I didn't mean any particular scale other than "the same as your previous graph", it's just much easier to flip back and forth to compare quickly visually if they two graphs are otherwise identical.

What are you looking for anyway? For someone to say "yep, looks good" or "no, you need to sort it out"? If so, it is what it is really. Only you can really say whether you think there is an audible impact to that amount of distortion in the upper mid bass. In my room & at those levels, I would say no but then the changes (that I think would be) required to deal with it are not feasible for me so my view is almost certainly prejudiced by that fact. I would expect someone like Jim, who has put that effort in (and then some!), to say yes it would be worth it. My point is that it's really all quite subjective at this point, do you have the desire/commitment/space/funds to treat your room?
As always, thanks for the reply. I don't see treating my room in the near future. Any way, I had the whole house to my self earlier today, so I decided to play those bass heavy scenes from the bass demo disc downloaded here at -5MV with subs 2db hot (I believe Aud set my subs trims 2db lower than reference as seen from REW graph), a 6db low shelf centered about 30hz along with 14hz high pass filter (from jriver mc20), all I heard was deep clean and loud bass that shook my chair pretty good. I could not detect any bad sound at all . I am quite happy with this latest Aud run (closed mic with all positions within 3 inches from MLP) and subs pEQ 80hz bump combo.
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post #13325 of 13348 Old 01-23-2015, 01:38 PM
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Quote:
Originally Posted by jim19611961 View Post
Left OR Right with subs.
Ok, I will post my mdat file with all of those measurements at -15MV later today. Thanks.
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post #13326 of 13348 Old 01-23-2015, 01:55 PM
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Quote:
Originally Posted by tvuong View Post
As always, thanks for the reply. I don't see treating my room in the near future. Any way, I had the whole house to my self earlier today, so I decided to play those bass heavy scenes from the bass demo disc downloaded here at -5MV with subs 2db hot (I believe Aud set my subs trims 2db lower than reference as seen from REW graph), a 6db low shelf centered about 30hz along with 14hz high pass filter (from jriver mc20), all I heard was deep clean and loud bass that shook my chair pretty good. I could not detect any bad sound at all . I am quite happy with this latest Aud run (closed mic with all positions within 3 inches from MLP) and subs pEQ 80hz bump combo.
I am a little confused now also. You say you like the way its sounds now (you said quite happy). You dont want to improve (treat) your room. So what it is you want help with?

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post #13327 of 13348 Old 01-23-2015, 02:08 PM
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@jim19611961 , here is the mdat file. All front three are crossovered at 90Hz. Thanks.

https://www.dropbox.com/s/x7rdhux718...0Jim.mdat?dl=0

Edit: To see if this latest run has less distortion.
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post #13328 of 13348 Old 01-23-2015, 05:25 PM
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Originally Posted by tvuong View Post
@jim19611961 , here is the mdat file. All front three are crossovered at 90Hz. Thanks.

https://www.dropbox.com/s/x7rdhux718...0Jim.mdat?dl=0

Edit: To see if this latest run has less distortion.
You have 2-3% in the midrange. I dont know whats up with your system, but while a certain amount of bass distortion may go unnoticed, in the midrange, there is clearly something up.

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post #13329 of 13348 Old 01-23-2015, 07:43 PM
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^^ thanks for taking the time. When you said midrange, you meant from my center, left or right?
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post #13330 of 13348 Old 01-23-2015, 08:07 PM
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Quote:
Originally Posted by tvuong View Post
^^ thanks for taking the time. When you said midrange, you meant from my center, left or right?
You shouldnt have to ask. Just look at the full range distortion measurements. Its pretty easy to see.

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post #13331 of 13348 Old 01-24-2015, 12:31 PM
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tvuong: for whatever reason I can't access your mdat files. But I just thought I'd throw this in, one more great use I've got out of the REW distortion measuring capability.

Anyway, I found that when some (quality) speakers measured elevated THD, and I mean over a small fraction of a %, it turned out that indeed the mid and "mid-bass" drivers were damaged. The higher the test level, the more the distortion increased, and I mean significantly increased, out of proportion. If your scenario seems a bit like this, do what you need to do to make sure it's not the amp channel that's at fault before saying it's the driver.

We also need to consider that speaker THD below 3% is traditionally actually considered "good". I can assure you that in a modern decent speaker, in the mids and highs at least, THD below 0.1% at a reasonable listening SPL (assuming capable amp), the levels we normally measure at, is very common. I'd say 1% is too much outside the bass range, if we're talking an indication of something "wrong", and not necessarily audibility to any specific individual.

Remember I can't see your graphs! Another clue to a damaged driver is look for the THD significantly peaking at a frequency (resonating). This could indicate a loose cone, or a damaged surround, or maybe even a damaged spider. Many modern drivers, and I'm talking even quite expensive ones, use glue to hold many (all!) of the parts together. I have seen this glue come loose in areas, and when fixed (quality adhesives) the distortion completely went away. It was kind of hard to find & figure out, until after I saw it the first time, but something to consider.

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post #13332 of 13348 Old 01-24-2015, 01:36 PM
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^^ Thanks. It could be the damage horn tweeter or mid range driver that shows distortion in graph. These are more than 20yrs old Klipsch speakers. The mid range drivers look to be in very good shape from what I can see. Any way, I am not hearing distortion at 10db higher than my norm level, I guest I am ok. I use this system for movies only. I might upgrade to some Crites' tweeters later.
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post #13333 of 13348 Old 01-24-2015, 02:17 PM
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^ I have never seen a damaged horn driver (even though I've had some for almost 40 years!) so I have no idea what might go wrong with them when they're showing a raised THD. If in fact there's any problem with them at all... One of the strengths of horn drivers is that they're...errr...strong.
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post #13334 of 13348 Old 01-24-2015, 03:14 PM
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Quote:
Originally Posted by jim19611961 View Post
Typically, the higher distortion will be found in nulls. And if your using processing (dsp, audyssey, eq) which is trying to boost nulls, then these places will have even higher distortion still.
No argument. Just want to add some further perspective.

If a speaker is outputting some low distortion at frequencies above and below a null, then it is reasonable to assume that the absolute level of the harmonic distortion products in the room is not actually elevated in the null region. The THD measures higher simply because the fundamental has been suppressed in the null. It's not like the speaker is actually under any additional stress or behaving with more non-linearity in the null region.

Until one tries to flatten a null with EQ. And that's generally not a good idea anyway, nothing to do with distortion, but other aspects of sound quality.

The implication is thus to ignore the distortion readings in the nulls, but pay a lot of attention to nulls when positioning and timing the speakers to try to minimize them where possible.

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post #13335 of 13348 Old 01-25-2015, 09:52 AM
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Originally Posted by Roger Dressler View Post
No argument. Just want to add some further perspective.

If a speaker is outputting some low distortion at frequencies above and below a null, then it is reasonable to assume that the absolute level of the harmonic distortion products in the room is not actually elevated in the null region. The THD measures higher simply because the fundamental has been suppressed in the null. It's not like the speaker is actually under any additional stress or behaving with more non-linearity in the null region.

Until one tries to flatten a null with EQ. And that's generally not a good idea anyway, nothing to do with distortion, but other aspects of sound quality.

The implication is thus to ignore the distortion readings in the nulls, but pay a lot of attention to nulls when positioning and timing the speakers to try to minimize them where possible.
No argument. Just want to add some further perspective.

Still, where one has a null, even with a flat distortion curve, one will hear more distortion because of the reduced output.

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post #13336 of 13348 Old 01-25-2015, 12:26 PM
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Originally Posted by jim19611961 View Post
No argument. Just want to add some further perspective.

Still, where one has a null, even with a flat distortion curve, one will hear more distortion because of the reduced output.
To what degree those harmonics are any more audible as the fundamental is suppressed is not easy to say under normal program listening. I wanted to avoid the subjective aspects and just comment on the operational mechanism behind REW's elevated distortion readings in the null regions.

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post #13337 of 13348 Old Yesterday, 06:08 PM
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Hi guys,
Question about frequency graph. Attached is the frequency graph of my center channel. I don't have sub included and have speakers set to large since I'm only concern as of now how my center channel on its own is performing. Took reading of only Center channel (attached). A few qustions

1 - Looking at the graph without any smoothing, I see some major dips. Can someone please interpret what these dips mean? How severe are they? Is my center channel performing bad?

2 - How do we handle these dips using room treatment? I do have 4" Wool panels (DIY). How do I know where to place them to fix the dip?

thx.
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post #13338 of 13348 Old Yesterday, 10:52 PM
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Originally Posted by SherazNJ View Post
Hi guys,
Question about frequency graph. Attached is the frequency graph of my center channel. I don't have sub included and have speakers set to large since I'm only concern as of now how my center channel on its own is performing. Took reading of only Center channel (attached). A few qustions

1 - Looking at the graph without any smoothing, I see some major dips. Can someone please interpret what these dips mean? How severe are they? Is my center channel performing bad?

2 - How do we handle these dips using room treatment? I do have 4" Wool panels (DIY). How do I know where to place them to fix the dip?

thx.
Hi SherazNJ,

When you test the center speaker without the sub, be sure it's set to LARGE on your pre/pro/receiver. I made the mistake of not disabling bass management and was wondering why the roll off was happening sooner.

Room modes are typically below 300Hz.

For the no smoothing graph, the frequency range is normally 15Hz to 300Hz. One is with REQ and the other without REQ.

You would normally do a center only, then center + sub to see how good the splice is.

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post #13339 of 13348 Old Yesterday, 11:18 PM
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Originally Posted by steveting99 View Post
Hi SherazNJ,

When you test the center speaker without the sub, be sure it's set to LARGE on your pre/pro/receiver. I made the mistake of not disabling bass management and was wondering why the roll off was happening sooner.

Room modes are typically below 300Hz.

For the no smoothing graph, the frequency range is normally 15Hz to 300Hz. One is with REQ and the other without REQ.

You would normally do a center only, then center + sub to see how good the splice is.
I did have the speaker set to large. I took reading from 80 instead 15 because 80 is the cross-over point and I wasn't interested on how the speaker is working with sub. I just wanted to get the speaker alone. Since have a cross-over at 80, didn't see any need to get that in the measurement. My main question was, how to interpret the graph that I attached? Is it bad or its normal? I know some here have a very smooth graph even without any smoothing but then they have a lot of room acoustic treatment applied. I only have first reflection covered for Left/Right/Top. No bass traps. I want to buy bass traps and use them but for that I need to know where the issue is. When we see impulse graph, we know that we need to cover reflection points to reduce them below -20 and the rest that are left, we place the panels around until we get the fixed. How do we fix frequency dips/peaks and what acoustic treatment is good? We are talking about mid-range here.

Thanks.
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post #13340 of 13348 Old Today, 02:58 AM
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Quote:
Originally Posted by SherazNJ View Post
I did have the speaker set to large. I took reading from 80 instead 15 because 80 is the cross-over point and I wasn't interested on how the speaker is working with sub. I just wanted to get the speaker alone. Since have a cross-over at 80, didn't see any need to get that in the measurement. My main question was, how to interpret the graph that I attached? Is it bad or its normal? I know some here have a very smooth graph even without any smoothing but then they have a lot of room acoustic treatment applied. I only have first reflection covered for Left/Right/Top. No bass traps. I want to buy bass traps and use them but for that I need to know where the issue is. When we see impulse graph, we know that we need to cover reflection points to reduce them below -20 and the rest that are left, we place the panels around until we get the fixed. How do we fix frequency dips/peaks and what acoustic treatment is good? We are talking about mid-range here.

Thanks.
SherazNJ,

The crossover point is not a brick wall and there is contribution from both the sub and speaker on either side of the crossover frequency. As you have more than one energy device that can produce bass, it would be better to have a combined response of both the center + sub to see the total response. Do you normally switch the sub OFF when watching a movie/music? If you're interested in seeing where the nulls are as well as the bass ringing within in the room, the waterfall graph and spectrogram will tell how.

Generally the guide says to obtain bass decay within 450ms; i.e. to the noise floor of the room. Understand that this is hard to do at lower frequencies; i.e. at 40Hz and below.

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post #13341 of 13348 Old Today, 04:21 AM
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Originally Posted by steveting99 View Post
Room modes are typically below 300Hz.
In any room the number of modes increases with frequency:

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Quote:
Originally Posted by SherazNJ View Post
1 - Looking at the graph without any smoothing, I see some major dips. Can someone please interpret what these dips mean? How severe are they? Is my center channel performing bad?
The dips could be floor bounce but I'm a neo at this. Try putting a quilt/duvet or something on the floor to see if they get better.

Assuming that the dips are caused by destructive interference, that is, like comb filtering.
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post #13343 of 13348 Unread Today, 07:29 AM
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Quote:
Originally Posted by SherazNJ View Post
Hi guys,
Question about frequency graph. Attached is the frequency graph of my center channel. I don't have sub included and have speakers set to large since I'm only concern as of now how my center channel on its own is performing. Took reading of only Center channel (attached). A few qustions

1 - Looking at the graph without any smoothing, I see some major dips. Can someone please interpret what these dips mean? How severe are they? Is my center channel performing bad?

2 - How do we handle these dips using room treatment? I do have 4" Wool panels (DIY). How do I know where to place them to fix the dip?

thx.
First of all, it is useless to measure as you have done, i.e. setting the center to large and taking the sub out of the equation. This is not how you are actually hearing the speaker, so why measure it this way? If you want real feedback, measure with the center set to small, and with the sub.

HST, frequency response anomalies are caused by the dimensions of your room, and the placement of the speakers WRT the room dimensions. You can address these peaks and dips by slight changes in speaker placements, if that is an option. Treatments are more effective at lessening bass resonance (with bass traps), and reflections (broadband treatments placed at key reflection points). Neither approach is particularly effective in controlling room-related modes outside of the modal region (where your center channel operates).

Of course, room EQ can assist in smoothing out frequency response in some cases. You don't mention whether you use EQ such as Audyssey
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post #13344 of 13348 Unread Today, 08:45 AM
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How do you guys decide exactly how "hot" you are running your subs?

-REW sweep level?
-Handheld SPL meter and internal tones?
-Handheld SPL meter and external tones?
-REW SPL meter and external tones?

Last night I used REW's signal generator set to Pink Noise/Sub Cal/-30db using output 3 (center channel) with the CC unplugged, MV at 0. From what I've read (specifically, advice from AustinJerry), this is the most accurate way to measure the level of the subs. Using this method and REW's SPL meter "logger", the subs measured between 5-6db higher than the L/C/R (80-81db). Is this the best way to do it?

I have the subs set 9db higher than Audyssey set them.

If I look at the REW sweep, it looks like my subs are running 8-10db (or more) hot:

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AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
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post #13345 of 13348 Unread Today, 09:01 AM
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Originally Posted by Alan P View Post
How do you guys decide exactly how "hot" you are running your subs?

-REW sweep level?
-Handheld SPL meter and internal tones?
-Handheld SPL meter and external tones?
-REW SPL meter and external tones?

Last night I used REW's signal generator set to Pink Noise/Sub Cal/-30db using output 3 (center channel) with the CC unplugged, MV at 0. From what I've read (specifically, advice from AustinJerry), this is the most accurate way to measure the level of the subs. Using this method and REW's SPL meter "logger", the subs measured between 5-6db higher than the L/C/R (80-81db). Is this the best way to do it?

I have the subs set 9db higher than Audyssey set them.

If I look at the REW sweep, it looks like my subs are running 8-10db (or more) hot:

Easy. I don't run my subs hot. I use Spears&Munsil test tones to check levels of speakers and combined subs with Audyssey turned on. I adjust everything so I get a 75dB reading on the REW SPL meter. With subs set to 75dB, my bass response is strong and even. I wouldn't want the sub levels any hotter.

Why do you run subs hot? Do you like bass thump?
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post #13346 of 13348 Unread Today, 09:03 AM
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Quote:
Originally Posted by AustinJerry View Post
First of all, it is useless to measure as you have done, i.e. setting the center to large and taking the sub out of the equation. This is not how you are actually hearing the speaker, so why measure it this way? If you want real feedback, measure with the center set to small, and with the sub.
Thanks for your response Jerry. I'm attaching a new one with Sub included, Audyssey On/Off and C set to small.

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HST, frequency response anomalies are caused by the dimensions of your room, and the placement of the speakers WRT the room dimensions. You can address these peaks and dips by slight changes in speaker placements, if that is an option. Treatments are more effective at lessening bass resonance (with bass traps), and reflections (broadband treatments placed at key reflection points). Neither approach is particularly effective in controlling room-related modes outside of the modal region (where your center channel operates).

This is exactly what I was looking for that is how to manage dips/peaks. Moving my center speaker back and forth, I am able to get better response than before but this is the best I have gotten so far.

Quote:
Of course, room EQ can assist in smoothing out frequency response in some cases. You don't mention whether you use EQ such as Audyssey
New attached graph is With/Without Audyssey. I"m thinking about miniDSP Dirac Live but haven't found much info on it yet. The fact that it allows one to control the frequency curve is very intriguing.

Audyssey didn't seem to do much for me as you can see in before/after graphs.
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Originally Posted by Alan P View Post
How do you guys decide exactly how "hot" you are running your subs?
I draw it into my target curve

in the event that I don't have that capability then I use the RTA with pink noise set to average over some decent no of samples, run it through channel 1 and then through channel 4 then compare the peak traces (RTA leaves a high watermark behind).
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Originally Posted by AustinJerry View Post
Easy. I don't run my subs hot. I use Spears&Munsil test tones to check levels of speakers and combined subs with Audyssey turned on. I adjust everything so I get a 75dB reading on the REW SPL meter. With subs set to 75dB, my bass response is strong and even. I wouldn't want the sub levels any hotter.

Why do you run subs hot? Do you like bass thump?
Apparently.

When the subs are set to 75db they just don't satisfy like they do at 80-81db. I know I'm not alone.

I see folks on here saying that they are running their subs "3db hot" or "6db hot", I was just wondering how they know how hot they are running. Because by one method I'm ~10db hot, by another I'm onyl ~5db hot that is all.

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
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