# REW Question



## pdxrealtor (Jun 30, 2013)

I need to replicate the exact (or as close as possible) same levelsl as a blu-ray clip I am playing, using the REW tone generator.

I need to play the LFE channel, and right left channels. 

I am hooked up with HDMI from laptop to the AVR. 

What settings should I use? Timing reference and dbfs settings come to mind. What do I set these at? Any other settings I need to change? 

Thanks!

EDIT* I think the highest sound level off a Bluray is 0 DBFS, and that includes peaks. Whereas in REW the highest I seem to be able to go is -3 DBFS. Also, the volume changes a good amount when you select the LFE channel - so - do I use the LFE or not? 

I'm plotting an impedance curve with a volt and amp meter. I need to best replicate the signal levels, using REW tones, I'm seeing in a specific movie scene


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## willis7469 (Jan 31, 2014)

Hey Matt, tried to pm this but I couldn't figure it out. That stuff was perfect. I have rotated it back in place, and wiped off the prints. 
Thanks again. I owe ya one. 
Btw, did you see I scored an SB2k? Awesome!
Ok, u can have ur thread back! Sorry.


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## pdxrealtor (Jun 30, 2013)

^^ Looks real good Willis! Glad it worked out. 

What's the SB2k you speak of?


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## willis7469 (Jan 31, 2014)

pdxrealtor said:


> ^^ Looks real good Willis! Glad it worked out. What's the SB2k you speak of?


I won half of the SVS giveaway! One) SB2000. 
Bkeeler win the PB2000. Woot!


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## pdxrealtor (Jun 30, 2013)

willis7469 said:


> I won half of the SVS giveaway! One) SB2000.
> Bkeeler win the PB2000. Woot!



NICE!!! :clap: That's awesome! 


Hey..... didn't you say you owe me one? :rofl2:


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## willis7469 (Jan 31, 2014)

pdxrealtor said:


> NICE!!! :clap: That's awesome! Hey..... didn't you say you owe me one? :rofl2:


did I say that? Lol yeah I do.


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## pdxrealtor (Jun 30, 2013)

Anyone who can help with the OP ?


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## EarlK (Jan 1, 2010)

Just about everyone who wants to balance "A" to "B" does it acoustically ( using identical test signals ) , while employing an SPL meter .

:sn:


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## pdxrealtor (Jun 30, 2013)

EarlK said:


> Just about everyone who wants to balance "A" to "B" does it acoustically ( using identical test signals ) , while employing an SPL meter .
> 
> :sn:


Maybe I wasn't clear - I edited my first post to help clarify. 

It's impossible to level match an actual movie scene and test tone, because they aren't identical. One is dynamic and one is static.


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## willis7469 (Jan 31, 2014)

Hey Matt, if your playing out of a htpc, there might be some kind of monitoring software you can run along side of the output section. Then you might be able to analyze in real time and set a benchmark. Wayne or Leonard might be good ones to ask. ...above my schoolin!


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## pdxrealtor (Jun 30, 2013)

willis7469 said:


> Hey Matt, if your playing out of a htpc, there might be some kind of monitoring software you can run along side of the output section. Then you might be able to analyze in real time and set a benchmark. Wayne or Leonard might be good ones to ask. ...above my schoolin!


I don't have an HTPC. 

REW has an RTA function. Hmmmm.... that would be back to doing things with an SPL meter though. 

The mini-dsp has meters, and that's actually exactly what I need is a level of signal. It would be better than trying to match things with the correct settings in REW, but the mini-dsp meters are to slow. 

I could video the meters and see if that allows my eyes to pick them up with more accuracy, or if the meters are just slow and it's not my eyes at all. 

I'd love to just put a volt meter on the line, but I don't think the volt meter is fast enough to handle dynamic content. It does have a PC app I need to download and test, but I just don't see it processing that fast of a moving signal.


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## JohnM (Apr 11, 2006)

Probably worth explaining why you want to do that/what you are seeking to achieve, there may be a more straightforward way to get the desired result.


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## 3ll3d00d (Jun 6, 2006)

Is this to determine exactly what level of signal causes your amp to shutdown?

I know you said you don't have an HTPC but perhaps someone you know does... there is an approach described here that shows you how to extract the mono mix sent to the sub a particular portion of a film. You can then get that into spectrumlab (if you have the right sort of PC) to see the exact nature of the content, there might be other such plugins available on windows though that can give a decent idea of the makeup of the track. 

I don't know how you'd translate a complex dynamic track into test tones though.


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## pdxrealtor (Jun 30, 2013)

Yes- I am trying to replicate war of the worlds pod scene, which at a couple points shuts down my amps when I have the low shelf and low boost applied. 

I think pink noise is the best way to accomplish this assuming I can ..- 

slow the pink noise PN (or pink noise) cycle down to a 1 second interval or greater and if possible map the frequency response using REW, and voltage / amperage with my meters. 

A forum member from another forum looked up some things in the REW manual. John, can you verify? 

From the REW manual -



> The PN sequences REW generates are optimised to have a crest factor (ratio of peak level to rms level) that does not exceed 6 dB.


Does this mean at -5 dbfs, while running pink noise PN, I would be hitting + 1 dbfs?


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## JohnM (Apr 11, 2006)

The signal peak cannot exceed 0 dBFS by definition, so if you played the Pink PN at -5 dB FS you would be clipping peaks by around 1 dB. If you want it louder though it is the volume you should turn up rather than the signal level.

A better level test signal is probably the CEA-2010, which is used for sub output level tests. It spans 1/3rd of an octave or so from its centre frequency. 

Don't quite get what you are trying to achieve with the volt/ammeters though, if you want to measure the sub's impedance use an REW impedance sweep.


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## pdxrealtor (Jun 30, 2013)

JohnM said:


> The signal peak cannot exceed 0 dBFS by definition, so if you played the Pink PN at -5 dB FS you would be clipping peaks by around 1 dB. If you want it louder though it is the volume you should turn up rather than the signal level.
> 
> A better level test signal is probably the CEA-2010, which is used for sub output level tests. It spans 1/3rd of an octave or so from its centre frequency.
> 
> Don't quite get what you are trying to achieve with the volt/ammeters though, if you want to measure the sub's impedance use an REW impedance sweep.



Playing around with a few things - difference in output watts with MY subs using various connection schemes at the amp is one major goal, the other is in fact impedance. 

Thank you for the link- I did come across that in a Google search, but I am using an HDMI and USB mic combo, so it did not seem possible. If I missed something please let me know. 

I suppose I could pick up a sound card setup. This would also allow me to measure the roll off in different devices in my chain, which doesn't seem possible with a HDMI/USB mic setup. 

Any recommendations on brands for the tools (sound card? Mic? Etc...) needed to do the impedance testing? 

The Impedance test using REW, is that done using a sweep like the SPL tests? 

3ll3dood gave me some insight on CEA testing, but I've been focused on the amplifiers so I haven't read up on it yet. And, as of now, I'm too familiar with it. I always thought it would be something one does after the system is properly dialed in.


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## 3ll3d00d (Jun 6, 2006)

The reason I started doing those tests using the cea-2010 bursts was exactly this reason, determine if/when my amp was clipping. It gives you a fairly safe way to do this as each tone is 6.5 cycles long so shouldn't melt anything. Meanwhile you can watch the distortion level rise and it is quite obvious when the system really starts getting stressed as each extra unit of dB on the fundamental produces a multiplier effect on the incremental amount of distortion (eg +1dB on fundamental produces +3dB on 2nd harmonic).

I think this is more straightforward, and more precise, than using dynamic or broader band content.

The other thing to bear in mind is that a shelf filter doesn't roll off. If you have ever increasing room gain and a low shelf filter and no hpf then you have some serious power requirements there on a film like wotw that has v low freq content. If you measure room gain then you could dial in the ulf boost you need more precisely. In my case, I think I actually need next to no boost below 18Hz whereas I used to think I needed a fair bit. Big difference in power required.


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## pdxrealtor (Jun 30, 2013)

I know where my amp clips, but sometimes when it clips it's shutting down. Why? Because I'm running a nominal 2 ohm load that we think is dipping lower than 2 ohms. DCR is 1.41. 

The amp is not supposed to shut down. Instead it's DDT circuitry kicks in. But it does allow a few moments of hard clip before doing so. This few moments is where I am shutting down - sometimes. 

I'm trying to as best I can figure out the actual impedance when the amp shuts down. 

You mentioned tones being 6.5 cycles long. How long is a cycle?


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## willis7469 (Jan 31, 2014)

Hey Matt, have you talked to peavey?


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## pdxrealtor (Jun 30, 2013)

willis7469 said:


> Hey Matt, have you talked to peavey?


Extensively. One of my amps even went back for evaluation. The actual designer of these amps has been not only helping me through out, he's been giving elementary lessons, and teaching me how to implement the possibly solutions, none of which he has an obligation to do. 

We (JD - amp designer) also discovered you can take an IRP2 series amp and parallel both output channels for a one ohm stable mono block! In situations like mine where I am pushing the amps limits this will help lesson the load on the amp and allow for a bunch more headroom. It's not done as much so one can run a 1 ohm load, but more so for what I just explained. 

So in my situation I can - recone for a 4 ohm nominal, add wire between amp and sub (resistance), run one amp per sub (parallel mode), or back off the boost.  

For now, because I'm so far into this 'learning' phasing, I want to play around with the different options even though I know the solutions available to me.


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## 3ll3d00d (Jun 6, 2006)

pdxrealtor said:


> I know where my amp clips, but sometimes when it clips it's shutting down. Why? Because I'm running a nominal 2 ohm load that we think is dipping lower than 2 ohms. DCR is 1.41.
> 
> The amp is not supposed to shut down. Instead it's DDT circuitry kicks in. But it does allow a few moments of hard clip before doing so. This few moments is where I am shutting down - sometimes.
> 
> ...


Cycle = period so 20Hz = 50ms and the cea-2010 tone therefore lasts a touch under 1/3s at 20Hz

I don't know why you need dynamic content for this, at least not as a first step. It seems like you would be better off establishing the real world performance under controlled conditions and then attempting to relate this to the failure conditions.

fwiw I find short cuts on debugging exercises like this often end up coding more time overall than doing it methodically step by step.


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## JohnM (Apr 11, 2006)

Yes, impedance measurement uses a sweep. The impedance does not depend on content so you can measure it separately from trying to determine what content trips your amp, but it will probably give a good pointer on its own. There is a thread here about making an impedance measurement jig.


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