Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 357 - AVS Forum | Home Theater Discussions And Reviews
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post #10681 of 28216 Old 07-01-2014, 01:56 PM
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^
There's definitely something wrong with those measurements. Check outputs, inputs and AVR modes first. Could also be blown tweeters - does L and R look the same?

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post #10682 of 28216 Old 07-01-2014, 02:14 PM
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Would it be worthwhile playing a sine wave at those frequencies and seeing if anything comes out of the speakers?
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post #10683 of 28216 Old 07-01-2014, 03:42 PM
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Quote:
Originally Posted by AustinJerry View Post
Please go to page 51 of the Guide. Both the EMM-6 and the UMIK-1 can be configured with sensitivity parameters, which will allow REW to automatically calibrate the mics.
Awesome! Thanks Jerry.
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post #10684 of 28216 Old 07-01-2014, 04:43 PM
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Originally Posted by artur9 View Post
Would it be worthwhile playing a sine wave at those frequencies and seeing if anything comes out of the speakers?
Definitely.
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post #10685 of 28216 Old 07-01-2014, 10:39 PM
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After doing some more testing, I think I'm more confused. Here's my close mic of the left tower tweeter vs the close mic of the center tower tweeter.
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They both have the same extreme roll-off, and from my earlier post you can see the right tower appears to be doing it too. [I think the center came in quieter than the left here because even though Audyssey is off, I usually tweak the levels manually after it runs.] Surely it's not possible for all three tweeters to be damaged, right? Just bought the speakers about 7 months ago and I don't think I drive them very hard because I don't like it incredibly loud and I'm afraid I'm going to damage something.
I also played several REW sine waves in that upper range and they all were very audible and clear at the MLP. To my ears, they didn't sound like they were 60 db down like the graphs show, but what do I know. As a side test, I also turned on the RTA and close mic'd my laptop speaker while playing a 12k sine wave, just to see if my UMIK-1 was working properly.
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Does everyone else's RTA look like this, with all the noise extending down into the negative db range? Could that be related to my roll-off?

Appreciate any new thoughts you might have.
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post #10686 of 28216 Old 07-01-2014, 10:43 PM
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Quote:
Originally Posted by markus767 View Post
^
Check outputs, inputs and AVR modes first.
I've been trying to think of any settings in my x4000 AVR that would lead to this. Anything specific I should check besides Audyssey and DEQ / Dyn Vol? I've had them all off for these tests.

Thanks!
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post #10687 of 28216 Old 07-02-2014, 12:44 AM
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Guys,

I've managed to carry out some low frequency (15Hz to 300Hz) on two different subs placed in the same location to gauge the difference in THD measurements.

The setup included placing the subs in the front left corner of the room - same location. The sub distance is the about the same (off by 0.1 ft) as advised by the AVR. The volume levels were different depending on the amp plate settings. The noise floor as advised by the calibrated UMIK-1 mic from CSL is just under 70 dB, a bit high as the handheld meter says 55dB.

KEF E301c center speaker was used in both instances. Main Volume kept constant at -15dB. Audyssey was engaged, Dynamic EQ and Dynamic Vol were OFF.

The first graph is that of the new Rythmik F12G. The maximum THD is just below the noise floor of 70dB with a maximum value of about 6.5%.

The second graph is that of the old HTIB boom box (Minstral). Notice that the THD is really high, with maximum value in the 270%. This is audible and the sound quality is very objectionable.

While these are two extreme examples of THD measurements for the sub, I'm not sure where to draw the line in terms of acceptability. I do prefer the sub that has the lower THD in sound reproduction.
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post #10688 of 28216 Old 07-02-2014, 05:23 AM
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Originally Posted by mcnewt View Post
After doing some more testing, I think I'm more confused. Here's my close mic of the left tower tweeter vs the close mic of the center tower tweeter.
Attachment 145170
They both have the same extreme roll-off, and from my earlier post you can see the right tower appears to be doing it too. [I think the center came in quieter than the left here because even though Audyssey is off, I usually tweak the levels manually after it runs.] Surely it's not possible for all three tweeters to be damaged, right? Just bought the speakers about 7 months ago and I don't think I drive them very hard because I don't like it incredibly loud and I'm afraid I'm going to damage something.
I also played several REW sine waves in that upper range and they all were very audible and clear at the MLP. To my ears, they didn't sound like they were 60 db down like the graphs show, but what do I know. As a side test, I also turned on the RTA and close mic'd my laptop speaker while playing a 12k sine wave, just to see if my UMIK-1 was working properly.
Attachment 145178
Does everyone else's RTA look like this, with all the noise extending down into the negative db range? Could that be related to my roll-off?

Appreciate any new thoughts you might have.
For comparison, here is a quick sweep using my PC speaker:



It does not exhibit the severe roll-off that your measurements show. Given that everything you measure is exhibiting the same roll-off, I suspect a component in the measuring system is at fault. It would be hard to conclude that every one of your speakers is faulty.

So, starting with the microphone calibration file, please check to make sure you have the 90-degree calibration file loaded properly:



Next, please confirm that you are pointing the mic towards the ceiling at ear height at the MLP when taking your measurements.

There are not any settings on the AVR that would cause the HF roll-off, AFAIK. You should be in Stereo mode, and I believe you already said Audyssey is off for the measurements. Are there any switches on the speakers, e.g. a "boundary mode" switch? Are the speakers pointed directly at the MLP, i.e. "toed in"?

Ruling out everything else, I would start to suspect either a faulty mic, or something wrong with your laptop's sound card circuitry.
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post #10689 of 28216 Old 07-02-2014, 05:24 AM
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Originally Posted by steveting99 View Post
Guys,

While these are two extreme examples of THD measurements for the sub, I'm not sure where to draw the line in terms of acceptability. I do prefer the sub that has the lower THD in sound reproduction.
Of course, that is the better one. I don't think its distortion is excessive (and it is the 2nd harmonic, not the 3rd, which is much lower).
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post #10690 of 28216 Old 07-02-2014, 05:26 AM
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Quote:
Originally Posted by steveting99 View Post
Guys,

I've managed to carry out some low frequency (15Hz to 300Hz) on two different subs placed in the same location to gauge the difference in THD measurements.

The setup included placing the subs in the front left corner of the room - same location. The sub distance is the about the same (off by 0.1 ft) as advised by the AVR. The volume levels were different depending on the amp plate settings. The noise floor as advised by the calibrated UMIK-1 mic from CSL is just under 70 dB, a bit high as the handheld meter says 55dB.

KEF E301c center speaker was used in both instances. Main Volume kept constant at -15dB. Audyssey was engaged, Dynamic EQ and Dynamic Vol were OFF.

The first graph is that of the new Rythmik F12G. The maximum THD is just below the noise floor of 70dB with a maximum value of about 6.5%.

The second graph is that of the old HTIB boom box (Minstral). Notice that the THD is really high, with maximum value in the 270%. This is audible and the sound quality is very objectionable.

While these are two extreme examples of THD measurements for the sub, I'm not sure where to draw the line in terms of acceptability. I do prefer the sub that has the lower THD in sound reproduction.
There is no substitute for a quality component. I am guessing that your old sub was only good down to about 40hz. A sub will typically exhibit high levels of distortion below its design frequency. This is especially true when boost is applied to those frequencies.

I have noticed that cheaper subs target maximum output only down to the 50-60hz range. These subs are often ported models where there response falls off sharply below 45hz or so. Once you get below the tuning frequency of the port, the woofer unloads and excursion limits are easily exceeded. Thus, the high distortion levels below the port tuning frequency. Some compensate some through a EQ subtraction at these low frequencies. But boost gain can override this.

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post #10691 of 28216 Old 07-02-2014, 07:56 AM
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Quote:
Originally Posted by AustinJerry View Post
For comparison, here is a quick sweep using my PC speaker:



It does not exhibit the severe roll-off that your measurements show. Given that everything you measure is exhibiting the same roll-off, I suspect a component in the measuring system is at fault. It would be hard to conclude that every one of your speakers is faulty.

So, starting with the microphone calibration file, please check to make sure you have the 90-degree calibration file loaded properly:



Next, please confirm that you are pointing the mic towards the ceiling at ear height at the MLP when taking your measurements.

There are not any settings on the AVR that would cause the HF roll-off, AFAIK. You should be in Stereo mode, and I believe you already said Audyssey is off for the measurements. Are there any switches on the speakers, e.g. a "boundary mode" switch? Are the speakers pointed directly at the MLP, i.e. "toed in"?

Ruling out everything else, I would start to suspect either a faulty mic, or something wrong with your laptop's sound card circuitry.
Yes, when I was testing at the MLP I had the mic on a boom pointed at the ceiling and I was using the narrow band 90-degree file from Cross Spectrum (with the sensitivity line copied over from minidsp.com). When close-mic'ing the individual drivers, I had the mic on the same boom about 1" away and was using the narrow band 0-degree file from Cross Spectrum (also with sensitivity copied in).
I'm not sure if the AVR was in Stereo mode. It might have been in one of the multi-channel modes I last played content in. Would that matter since I'm telling REW to just test the Left tower and my sub amp is off?
No switches on the speakers anywhere.
Yes, Audyssey is off.
The speakers are currently facing straight, but I ran sweeps earlier with toe-in toward the MLP and there was no discernible difference in frequency response.

On page 49 of the REW guide, I can see the signal in your RTA hits 0 around 1,000 Hz like mine. If you change your y-axis to start at -60, does yours show all the noise in the higher frequencies? Why would there be any signal less than 0db?

I'll see if I can find a different computer to run REW on and hopefully rule out a soundcard issue.
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post #10692 of 28216 Old 07-02-2014, 08:01 AM
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I finally got a laptop to run REW with HDMI instead of out the headphone jack of my PC.

Hooked it all up last night for a measuring session and things seemed to work just fine. Only thing - when I measure the FL+SUB, FR+SUB or CENTER+SUB my output level is about 10db lower than when I measure subs only. Any idea what would cause this?

Also, when I used to measure with the ol' headphone jack, I always had the AVR in STEREO or PLIIx mode (and had to plug/unplug the FL/R/C speaker cables as needed). Should I be using MULTI CH 7.1 now instead (seems to be the logical choice)?
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post #10693 of 28216 Old 07-02-2014, 09:55 AM
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when I measure the FL+SUB, FR+SUB or CENTER+SUB my output level is about 10db lower than when I measure subs only. Any idea what would cause this?
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post #10694 of 28216 Old 07-02-2014, 10:00 AM
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Thanks Markus, that makes sense now.

So, when I'm measuring CH4 in REW it's the LFE channel only?

When I measure the FL+SUB (CH1) I should raise the MV 10db?

Is this the only way to get the graphs to match up?
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post #10695 of 28216 Old 07-02-2014, 11:08 AM
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Originally Posted by Alan P View Post
Thanks Markus, that makes sense now.

So, when I'm measuring CH4 in REW it's the LFE channel only?

When I measure the FL+SUB (CH1) I should raise the MV 10db?

Is this the only way to get the graphs to match up?
why do you want to measure the LFE channel only?
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post #10696 of 28216 Old 07-02-2014, 11:15 AM
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Originally Posted by Alan P View Post
Thanks Markus, that makes sense now.

So, when I'm measuring CH4 in REW it's the LFE channel only?

When I measure the FL+SUB (CH1) I should raise the MV 10db?

Is this the only way to get the graphs to match up?
When you send the signal to the LFE input, the AVR applies a 10dB boost. The subwoofer output will be 10dB higher. If you send a signal to L for example then the level of the L speaker output and subwoofer output should measure the same.

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post #10697 of 28216 Old 07-02-2014, 11:47 AM
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Originally Posted by 3ll3d00d View Post
why do you want to measure the LFE channel only?
I don't...do I??

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Originally Posted by markus767 View Post
When you send the signal to the LFE input, the AVR applies a 10dB boost. The subwoofer output will be 10dB higher. If you send a signal to L for example then the level of the L speaker output and subwoofer output should measure the same.
Are you saying that the combined level of the L speaker and the sub (CH1) should be the same as the sub alone (CH4)?

I'm getting more confused....
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post #10698 of 28216 Old 07-02-2014, 11:52 AM
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Are you saying that the combined level of the L speaker and the sub (CH1) should be the same as the sub alone (CH4)?
No. Check the flow chart again.
If you send a test signal to channel 4 then the AVR considers this as an input coming from the LFE channel and boosts it by 10dB. The signal going to the sub is 10dB higher than the input signal.
If you send a test signal to L and bass management is active (speaker is set to "small") then higher frequencies go to the L speaker and lower frequencies go to the sub. Nothing is boosted. Level is the same.

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post #10699 of 28216 Old 07-02-2014, 11:54 AM
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Can someone just tell me which HDMI Audio Out I should use for sub only, sub+L, sub+R, sub+L/R and sub+center measurements?? I can't seem to find this info anywhere.

From just playing pink noise and changing the outputs, I'm guessing it's:

SUB+L
HDMI OUT 1

SUB+R
HDMI OUT 2

SUB+CENTER
HDMI OUT 3

SUB ONLY
HDMI OUT 4

Or am I totally off base here?

Also, which surround mode should I be in when taking these measurements?
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post #10700 of 28216 Old 07-02-2014, 11:57 AM
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Originally Posted by markus767 View Post
No. Check the flow chart again.
If you send a test signal to channel 4 then the AVR considers this as an input coming from the LFE channel and boosts it by 10dB. The signal going to the sub is 10dB higher than the input signal.
If you send a test signal to L and bass management is active (speaker is set to "small") then higher frequencies go to the L speaker and lower frequencies go to the sub. Nothing is boosted. Level is the same.
OK, got it. Thanks again Markus...sometimes I can be a bit thick.

So, how do you guys compare graphs of subs only and subs+L or R speakers? Seems to me like the 10db difference would make it a little difficult to read since you can't overlay them. Or, is this not a necessary thing??
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post #10701 of 28216 Old 07-02-2014, 12:08 PM
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Originally Posted by Alan P View Post
Can someone just tell me which HDMI Audio Out I should use for sub only, sub+L, sub+R, sub+L/R and sub+center measurements?? I can't seem to find this info anywhere.

From just playing pink noise and changing the outputs, I'm guessing it's:

SUB+L
HDMI OUT 1

SUB+R
HDMI OUT 2

SUB+CENTER
HDMI OUT 3

SUB ONLY
HDMI OUT 4

Or am I totally off base here?

Also, which surround mode should I be in when taking these measurements?
If you want to avoid the 10dB boost, avoid using HDMI out 4. Send the test signal to HDMI out 1, for example, and disconnect the wire to the left speaker. That will measure the sub without the 10dB boost.
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Originally Posted by Alan P View Post
OK, got it. Thanks again Markus...sometimes I can be a bit thick.

So, how do you guys compare graphs of subs only and subs+L or R speakers? Seems to me like the 10db difference would make it a little difficult to read since you can't overlay them. Or, is this not a necessary thing??
Another way to skin the cat would be to open the REW Controls tool in the measurements panel, select "Measurements Offsets", and apply -10 dB to the sub measurement.
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Originally Posted by Alan P View Post
I don't...do I??
you might do, you might not I can't think of many reasons to use the LFE channel for a measurement, the only times I can remember using it was to verify I had my LFE boost setup correctly (I use a PC and getting LFE right is a black art at times). Generally speaking if you want a "full" range measurement of your sub then it's better to use a main channel, turn off (or disconnect) the relevant main speaker & up the XO (if required). If you want to measure the sub with the XO engaged then you just disconnect/turn off the main channel.
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I don't think there is a fundamental difference between sending an REW test signal to the mains plus subs, and turning the mains off, and sending a signal to the LFE channel. Both would measure sub output. For some, the convenience of not having to manually disconnect the mains speaker leads might make it more convenient to use the HDMI4 approach, compensating for the 10dB boost, of course.
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post #10705 of 28216 Old 07-02-2014, 12:56 PM
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Quote:
Originally Posted by AustinJerry View Post
I don't think there is a fundamental difference between sending an REW test signal to the mains plus subs, and turning the mains off, and sending a signal to the LFE channel. Both would measure sub output. For some, the convenience of not having to manually disconnect the mains speaker leads might make it more convenient to use the HDMI4 approach, compensating for the 10dB boost, of course.
the other main difference is the filter applied to that channel, the LFE usually has a high order low pass with a max setting of 120Hz whereas the mains are often shallower and can be set to rolloff much higher. It is a lot more convenient if you have a separate power amp mind you.
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post #10706 of 28216 Old 07-02-2014, 01:00 PM
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Originally Posted by AustinJerry View Post
I don't think there is a fundamental difference between sending an REW test signal to the mains plus subs, and turning the mains off, and sending a signal to the LFE channel. Both would measure sub output. For some, the convenience of not having to manually disconnect the mains speaker leads might make it more convenient to use the HDMI4 approach, compensating for the 10dB boost, of course.
The difference is that the LFE might have its own low pass filter whereas the low pass of redirected bass is coupled to the channel's crossover setting.

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post #10707 of 28216 Old 07-02-2014, 01:21 PM
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Quote:
Originally Posted by AustinJerry View Post
If you want to avoid the 10dB boost, avoid using HDMI out 4. Send the test signal to HDMI out 1, for example, and disconnect the wire to the left speaker. That will measure the sub without the 10dB boost.
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Another way to skin the cat would be to open the REW Controls tool in the measurements panel, select "Measurements Offsets", and apply -10 dB to the sub measurement.
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Originally Posted by 3ll3d00d View Post
you might do, you might not I can't think of many reasons to use the LFE channel for a measurement, the only times I can remember using it was to verify I had my LFE boost setup correctly (I use a PC and getting LFE right is a black art at times). Generally speaking if you want a "full" range measurement of your sub then it's better to use a main channel, turn off (or disconnect) the relevant main speaker & up the XO (if required). If you want to measure the sub with the XO engaged then you just disconnect/turn off the main channel.
OK, I get it now.

One more thing - is there an easy way to measure L+R+Sub using HDMI? For the life of me, I can't figure out how it would be done....I'm sure it's something really easy to make me feel stupid once again.
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post #10708 of 28216 Old 07-02-2014, 01:47 PM
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Quote:
Originally Posted by Alan P View Post
OK, I get it now.

One more thing - is there an easy way to measure L+R+Sub using HDMI? For the life of me, I can't figure out how it would be done....I'm sure it's something really easy to make me feel stupid once again.
Of course. Send a signal to HDMI1 and 2, and by virtue of bass management, frequencies below the crossover are directed to the sub channel.
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post #10709 of 28216 Old 07-02-2014, 02:15 PM
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I'm at work so I don't have REW in front of me, but last night I couldn't figure out how to send a signal to more than one HDMI output...the list in the drop down only let me choose one at a time.
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post #10710 of 28216 Old 07-02-2014, 02:37 PM
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This is covered in the Guide, Alan. Simply choose the second output from the Timing Reference Output drop-down:

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