# External sweep with REW



## jdebonth

*Feature Request: External sweep with REW*

_EDIT: Modified title to feature request._

Is it possible to play a sweep externally from CD or another computer when taking a REW measurement?

Reason why I want to do this is that I want to confirm the digital EQ parameters I have applied in my audio playback software have flattened out the freq response as REW has predicted.

Thanks


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## SAC

Simply make a full range sweep of the system with REW!

The filters determined in that section of the program have nothing to do with the measurement portion of the program!


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## jdebonth

Sorry I was not clear enough in my first post.

I have measured my system with REW, found some peaks in the 20-100hz region, and have then created filters to flatten them.

On my playback system (macmini running PureMusic) I then apply these filters using a VST EQ plugin, and all music played back on the macmini through the PureMusic playback software has the EQ applied and the 20-100hz region sounds alot better. The modes seem to have been tamed.

But I now want to confirm - to see the frequency response of my system, with the digital EQ applied. Running a sweep in REW would not include the digital EQ so I would just get the same result. What I would like to do is play a recorded sweep (WAV file) through PureMusic (with the EQ VST active) and then have REW simply record and show my the data. I.E. REW would 'wait' for the sweep to come and simply process and display the measurement data. In theory this should now look the same as the 'predicted' result from within REW when making the filters.

Hope that makes sense!


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## Wayne A. Pflughaupt

One way you could do it would be to get a broadband pink noise signal into PureMusic, then use REW’s RTA feature.

Regards,
Wayne


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## jdebonth

Wayne A. Pflughaupt said:


> One way you could do it would be to get a broadband pink noise signal into PureMusic, then use REW’s RTA feature.
> 
> Regards,
> Wayne


Thanks Wayne, I have done this but really I would like to take sweeps so I can do detailed analysis.

I guess it's not possible? Maybe I should submit a new feature request....


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## MarkusBonk

+1
That's exactly what I want to do as well


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## RHA

Google and download Binks Audio Test CD. Should do what you want to do.


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## jdebonth

RHA said:


> Google and download Binks Audio Test CD. Should do what you want to do.


Am I being unclear or are people not reading my posts? 

RHA- I have plenty of sweep tones, thanks anyways.


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## JohnM

This is on my list of features to implement, near the top.


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## jdebonth

JohnM said:


> This is on my list of features to implement, near the top.


John, great! I will eagerly await this . Fantastic software and forum support!


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## tols1

I'm curious about this as well. My problem is measuring my system in 5.1 configuration. The fronts and sub is ok, but I'm having trouble measuring the center and surround channels, one by one.

When using the multichannel inputs on the AVR (Yamaha RXV767) all eq and other DSP-curciuts are bypassed. With an external sweep source, one could use a multichannel calibration disc.

EDIT: seems JohnM managed to write a reply before me. Looking forward to the new functionality


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## rewjack

jdebonth said:


> Thanks Wayne, I have done this but really I would like to take sweeps so I can do detailed analysis.
> 
> I guess it's not possible? Maybe I should submit a new feature request....


The same request for me and many I would think.

Can that be done?


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## jdebonth

Glad to see this thread is still active and that there is widespread interest in this.


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## ccclapp

JohnM said:


> This is on my list of features to implement, near the top.


Fabulous!!!

*John, are you able to advise on the below?*

In the meantime, Im doing tests to determine if running live REW sweeps through JRiver MC loopback mode will yield valid results. My purposed workflow is:

1) Take measurements in REW in standard fashion to obtain "Before" results
2) Create adjustment filters in REW or otherwise
3) Load adjustments into JRiver MC 64 bit convolution engine

http://yabb.jriver.com/interact/index.php?topic=68828.0

4) Run new live sweeps in REW patched through JRiver loopback feature (with convolution applied) to measure "After" results

http://yabb.jriver.com/interact/index.php?topic=70242.0

5) Compare "before and "after" results

My question is, whether JRiver loopback will add time domain issues that will skew "after" results. If so can this be mitigated by doing either or both of:

A) Doing "soundcard" calibration running through JRiver MC loopback to offset any influence, and/or:
B) Doing BOTH the "before" AND "after" measurements through JRiver MC loopback, so no new variable is introduced between before/after?


*Also John, could you advise what measurement/graph in REW I'd use to determine if loopback is altering the signal time domain or otherwise?, In other words, if I were to compare two identical measurements, one straight and one in loopback, what REW test would I do to determine if they differ, and by how much??*

Thanks!!


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## JohnM

ccclapp said:


> My question is, whether JRiver loopback will add time domain issues that will skew "after" results.


What do you mean by "time domain issues", delay? Any delay difference would not affect the SPL response.


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## ccclapp

JohnM said:


> What do you mean by "time domain issues", delay? Any delay difference would not affect the SPL response.


By "time domain" (vs frequency domain) issues I mean delay, phase change, etc. All the things that show up in the waterfall, excess group delay, etc. I am not an expert in these things, but I understand the world of audio measurements generally includes two components, frequency domain and time domain, possibly you use different labels (or Im just very confused). 

My concern about using JRMC loopback mode when measuring convolution-corrected sweeps in REW (reflecting the corrections), is that the measurements may be out of phase and or show delay as compared to the pre-corrected REW measurements (which do not go through loopback, but instead go to the measurement soundcard).

Am I making myself clear, or not? Does any of this matter? Does the REW mic loopback solve all of these time-related issues?

The context of all of this, is trying to create and compare X/Os and then room correction in REW/Audiolense/Acourate. I want to use REW for baseline measurements of "before and "after" corrections. Because REW requires "live sweeps" vs external (as of today), I intend to play your measurement sweeps through JRMC convolution by means of its loopback feature. This way I can compare XO's/DRC convolution filters produced in REW, Audiolense, Acourate, etc, with each other and against the uncorrected signal. I will be able to see more than FR and can also look at excess group delay, waterfall, phase, etc.

Should I be thinking about this some other way?

Thanks


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## JohnM

ccclapp said:


> Does any of this matter?


No. There are lots of time delays when making measurements, from buffering and processing delays in various pieces of equipment to the time-of-flight delay from speaker to mic. Use the "Estimate IR Delay" feature in REW to remove the delays from each measurement.


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## jdebonth

Perhaps a quick and easy way to implement this would be to allow a set of parametric EQ filters to be loaded (or manually entered) in the 'Measurement' dialogue window which would then be applied on the sweep? If the resulting measurement is then flat it would confirm proper setup of EQ filters...


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## MarkusBonk

Another quick way of getting this to work, at least for me, would be if I could save the sweep as a wav to play back through JRiver. REW could then be "fooled" into thinking it is playing the sweep...


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## Wayne A. Pflughaupt

MarkusBonk said:


> Another quick way of getting this to work, at least for me, would be if I could save the sweep as a wav to play back through JRiver. REW could then be "fooled" into thinking it is playing the sweep...


See second post here:
http://www.hometheatershack.com/forums/rew-forum/58514-measuring-software-eqed-response.html

Regards,
Wayne A. Pflughaupt


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## MarkusBonk

Wayne A. Pflughaupt said:


> See second post here:
> http://www.hometheatershack.com/forums/rew-forum/58514-measuring-software-eqed-response.html
> 
> Regards,
> Wayne A. Pflughaupt


One needs an REW sweep so that we can do further analysis on the measured result. If one had a .wav of the real sweep REW wouldn't know that it was being played by another source i.e. one presses measure and starts the second source almost simultaneously. This is I agree a hack but it would be a temporary workaround for now.


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## jdebonth

Would that work? I.e. hit 'measure' in REW and then play a sweep of the same length externally? Would it matter/affect the result if there was a 1 or 2 second delay in the playback of the external sweep?

WAV files of sweeps can be found in many places. The measurement settings in REW could be set to mirror the sweeps properties (volume and length)? Perhaps the external sweep just needs to be of shorter length than the REW sweep settings so that the full sweep plays during the measurement period? Wonder if this would work... JohnM or other developers could you please comment?


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## JohnM

jdebonth said:


> JohnM or other developers could you please comment?


You would need to capture the exact sweep REW produces to get a valid result and match the timing within a second or so, tricky to achieve. I'll get around to providing solutions in time, but this is a development team of one I'm afraid. 

REW's predicted EQ responses are generally very accurate (I made them that way to save the bother of lots of redundant verification measurements), but the RTA check already suggested would provide a quick check of whether the predicted responses are correct - make sure to measure from the same location as used for the uncorrected measurement.


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## EarlK

- An "open front end" would be somewhat intriguing ( but it's not a game-changer as far as I'm concerned ) .

- ( OTOH ) , I'd like to see REW have the ability to host VSTs for convolving EQ exports ( just before the signal leaves the program on the way to the soundcard ) . 

- In lieu of that ever happening , here's my work-around ( to see the consequences of applied EQ filters ) ;


















- One can see ( in the second pic ) a convolved sweep of the EQ filters ( as created by REW & then exported as a mono wave file ) . 
- *"Green"* is the speaker response as captured ( by someone over at GS ) , *"Orange"* is what the EQ filter itself looks like .
- *"Orange"* was captured using the SoundCard calibration ( loopback ) protocol .

- This setup ( software-wise ) is reasonably stable & costs less than $100.00 ( for both VAC & ConvoBoy ) .

:sn:

Oh ( I almost forgot ) , here's the REW side of it ( ie; the preferences window ) .


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## MarkusBonk

JohnM said:


> You would need to capture the exact sweep REW produces to get a valid result and match the timing within a second or so, tricky to achieve. I'll get around to providing solutions in time, but this is a development team of one I'm afraid.


Well, actually, I use a similar method to measure multiple locations simultaneously: Two REWs, two sound cards, two mics, and the sound card that drives the speakers provides the loop back for both sound cards. This appears to work very reliably: the results make sense and are reproducible.


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## ricardo_lee

MarkusBonk said:


> Another quick way of getting this to work, at least for me, would be if I could save the sweep as a wav to play back through JRiver. REW could then be "fooled" into thinking it is playing the sweep...


John, an easy way to complete the loop and enable the full processing power of REW's log sweep mode is to allow the *processing to be done on a WAV file*. The steps would be as follows.


Generate the sweep and save to a WAV file as Markus suggests
Playback and record this signal using a DAW like Audacity
Edit the recorded waveform so it includes the start & end of the sweep with say 200 samples before & after
The new facility then processes this edited WAV file with the same sweep settings.
I do the above with my crude software to measure microphones.

You could burn the WAV to a CD and play it back too. This is subject to the possibility that the clocks aren't EXACTLY in synch but the error is unlikely to do more than make the impulse response slightly fuzzy for sweeps up to say 14s. _Excuse my imprecise terminology._


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## EarlK

Good Post Ricardo ! Thanks !

- I believe I now stand corrected on ( challenging ) the utility of an opened up front-end ( into REW ) .

- Still, I'd like more at the back end ( as mentioned above ) .

Cheers :sn:


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## MarkusBonk

Attached is a proof of concept.
An REW sweep was recorded - that was the tricky bit. The REW calculated EQ parameters were plugged into the audio playing software and then the sweep played back, with REW thinking it was doing a measurement sweep.










And the equalized waterfall


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## Chad B

Any progress on external sweep compatability? I see there are some sweeps in the download section but they are not full range.


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## JohnM

No, not yet. Still on my list though.


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## Dragon777

Hi John,

I am also very interested in this feature.
Do you have any estimation about when it might come to life?

Thanks
D


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## JohnM

Afraid not, sorry.


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## guido310

Hi, i am just starting to approach measurment...
I have Jriver 19 and Audiolense, plus REW in a Wint 64 bit PC equipped with Lynx AES 16 soundcard and extenal Lucid DAc
I am just at the step of configuring biamplifications of the speakers (7.2 with fronts and back surround biamped for a total of 11 channels out of 16 being used in lynx AES) using Jriver crossovers...it seems to work well 
Now i am wondering which is the best way of making measurments with REW and AUDIOLENSE considering i need to have all the audio routed by Jriver
Starting from REW....connect calibrated mic to analog input of Lucid DAC, converting to AES, recording trough Lynx aes in 1+2 i should be able to have ASIO loopback (or using the new feature of Jriver as ASIO driver) 
in JRIVER (or wasapi) of REW's sweeps
Same for Audiolense (after ebnabling different play and recording)


Is this correct approach?

Thanks


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## jdebonth

Hi John, any updates on this? Cheers, Joost


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## Wull

JohnM said:


> No, not yet. Still on my list though.


Hi John. Did this ever get looked at?

I to need away to play an external REW sweep though jriver.


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## jdebonth

I am also still very much in need of this feature...


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## 3ll3d00d

Wull said:


> Hi John. Did this ever get looked at?
> 
> I to need away to play an external REW sweep though jriver.


Why can't you use jriver wdm or asio line in?


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## Wull

3ll3d00d said:


> Why can't you use jriver wdm or asio line in?



I tried this 'a good while back' but couldn't get it to work. I do use the wdn driver when watching 3D films.

I am using an AES16e S/C in my HTPC. When running REW, I need to be able to feed the analogue REW signal from my USBPre1.5 back through the PC/AES to the processor using jRiver. 'It's so I can measure multiple sub's'.

I am not sure this is possible. I did wander if I could use 1 PC to take the measurements and another PC to play a REW sweep?


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## JohnM

Sorry, still no progress on this.


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## Wull

3ll3d00d said:


> Why can't you use jriver wdm or asio line in?


would using a usb mic work?


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## jdebonth

Maybe easier to implement: allow some EQ parameters on the sweep generated from within REW. This will allow us to confirm the predicted EQ filters are indeed flattening out the response (and also measure ED-ed response in other locations).


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## Lumen

JohnM said:


> I'll get around to providing solutions in time, but this is a development team of one I'm afraid.


Thank you for your immense contributions, John! Chalk me up as another user who could definitely benefit from External Sweep functionality. :wave:


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## jtalden

Wull said:


> I tried this 'a good while back' but couldn't get it to work. I do use the wdn driver when watching 3D films.
> 
> I am using an AES16e S/C in my HTPC. When running REW, I need to be able to feed the analogue REW signal from my USBPre1.5 back through the PC/AES to the processor using jRiver. 'It's so I can measure multiple sub's'.
> 
> I am not sure this is possible. I did wander if I could use 1 PC to take the measurements and another PC to play a REW sweep?


It is possible to; "use 1 PC to take the measurements and another PC to play a REW sweep". This is the process I have been using. So far as I am aware, I'm the only one routinely doing it this way. 

It is comparatively common to use the routing features now available within the JRiver. There are also other utilities to address rerouting of the signal within one PC. I haven't done that way so cannot help in how to do that however. Apparently JRiver forums have discussed and supported this approach reasonably well though. I would guess that that forum is your best resource. 

The basic process to use 2 PC's is likely even more difficult to setup. It is also more likely to be problematic in use than the JRiver option. When using 2 PCs, if the timing of the measurement process is wrong, then the low frequencies or high frequencies can be distorted. It takes some practice and experience to get the timing right. 

The basic Process for using 2 PCs:
> Record the desired REW sweep in Audacity or similar program.
> Edit it as needed to contain say; 3.5s of silence before the sweep starts.
[I also added maybe 5s at the end, but I don't know if that is really needed. It just seem like a safe approach.]
> Save it in either wav or flac format being sure that it is the same sample rate as the original sweep.
> Play the file on one PC using any music server that shows the track timing as it plays. 
[I use Foobar2000 over DLNA to my Pre/Pro since that is the remote music server I use for my music.]
> Play the sweep file and when the timing shows '3s' (0.5s before the sweep starts) start the measurement on other PC. If the LF or HF of the resulting measurement looks to be truncated or distorted then adjust the start timing of the measurement relative to the timing indicator as necessary. [In my setup I can select measure just after 3s displays on the music server.] In my case I find there is maybe 0.5s tolerance in the initiation of the measurement on the 2nd PC.

We need to be sure that REW settings on the PC used to capture the measurement are the same as those that were used to record the sweep. Any change to the start or stop frequency or sample rate will definitely corrupt the measurement. 

This sounds easy, but I had a lot of problems getting the file setup correctly and learning how to get reliable measurements. 

An example below from my setup shows the SPL of the internal sweep and the external (DLNA) sweep using Foobar with an active FIR phase correction filter. The SPL differences shown are trivial as there are no SPL filters in my situation. The Phase chart however shows the impact of the phase correction filter. 

















Again, using the JRiver routing capabilities is probably the better choice, but it is possible to see the impact of filters implemented within a music server using either method.


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## Wull

Thanks jtalden. I think I shall wait for my REW 'guru' to take a look at this when his next round. 

Looking at the jRiver 'loopback' option. I just cant see how you get the REW sweep to run through jRiver when it's going from my REW/preamp/processor


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## AudiocRaver

Although I do not use it routinely, I have done it the jtalden way on occasion and it works like a charm.


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## Wull

AudiocRaver said:


> Although I do not use it routinely, I have done it the jtalden way on occasion and it works like a charm.





> Record the desired REW sweep in Audacity or similar program.


Hi. Where could I get a sweep that runs from say 10 - 200 hz?


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## subterFUSE

*Re: Feature Request: External sweep with REW*

This is something I have been wanting to try, although I think I can just use the RTA and a pink noise track for my purposes.

The goal is to confirm if the output from my sources is flat. Specifically, I have a FLAC media player with an optical out. It has no input so I can't route the REW live signal into it. But I could make a pink noise WAV file and load that onto the player, and then run the optical cable into my sound card. I think the only caveat is I must use REW on a PC to access the optical input on my sound card, correct? I prefer the Mac version but don't recall seeing the optical input as an available option in Mac REW.


Sent from my iPhone using Tapatalk


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## 3ll3d00d

Wull said:


> Looking at the jRiver 'loopback' option. I just cant see how you get the REW sweep to run through jRiver when it's going from my REW/preamp/processor


the jriver asio line in or WDM option means the signal chain is 

REW -> jriver -> DAC 

you don't go out to a prepro and then back into jriver (well you could if you really wanted to and had the appropriate hardware)


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## AudiocRaver

Wull said:


> Hi. Where could I get a sweep that runs from say 10 - 200 hz?


I will make you one later today, just take a minute. I assume you want 48k sample rate, 16 bit, -20 dB, and the standard 256k length? It has to match your REW settings precisely, or REW won't be able to make sense of it. I will make 2 sweeps, one for left and one for right. Do you want a third that goes to both left and right together, for subwoofer use?


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## Wull

AudiocRaver said:


> I will make you one later today, just take a minute. I assume you want 48k sample rate, 16 bit, -20 dB, and the standard 256k length? It has to match your REW settings precisely, or REW won't be able to make sense of it. I will make 2 sweeps, one for left and one for right. Do you want a third that goes to both left and right together, for subwoofer use?


Hi AudiocRaver. Many thanks for the offer, I really appreciate the help. However it appears I have 'finally' got REW running through jRiver now so I will not require the sweep. 

cheers.

Will


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## Wull

3ll3d00d said:


> the jriver asio line in or WDM option means the signal change is
> 
> REW -> jriver -> DAC
> 
> you don't go out to a prepro and then back into jriver (well you could if you really wanted to and had the appropriate hardware)


Think I may have got it working


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## AudiocRaver

Super. Sometimes it takes a few tries.


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## Wull

3ll3d00d said:


> the jriver asio line in or WDM option means the signal chain is
> 
> REW -> jriver -> DAC
> 
> you don't go out to a prepro and then back into jriver (well you could if you really wanted to and had the appropriate hardware)



Matt. Is there a way I can also use the 'loopback as timing reference' through jRiver?


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## AudiocRaver

You can loop back from anywhere you want to in your system, as long as you take proper care for signal levels. Even at the AVR speaker output (be REAL careful there!).


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## vidareje

Any progress implementing a convolver in REW? 
I'm really curious to get at detailed analysis of my system with Audiolense XO corrections. I have done the pink noise/RTA test and it looks really promising, but it would have been very interesting to see a frequency sweep, waterfall, impulse response, excess group delay +++ I do not have a jriver license (trial period has expired) and don't want to spend 50$ for a single measurement


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## 3ll3d00d

*Re: Feature Request: External sweep with REW*

Doesn't audiolense let you measure with the filter in place?

Alternatively you could convolve the sweep with your filter offline and use this as the external measurement sweep.


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## vidareje

Audiolense only gives a simulated response, which is supposed to be quite good. I could do something like you suggest, do you think it would be possible to simply play a 20-20000Hz sweep through my SBT and at the same time do a measurement with REW? I guess there would be some timing issues, but that might be alright?


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## 3ll3d00d

I would expect the audiolense simulation to be exactly correct if you haven't moved the mic at all. If you want to measure the results across multiple positions then you need to actually measure.

My point is to use an offline convolver (e.g. convolver.sourceforge.net) and feed your convolved sweep in like http://www.hometheatershack.com/for...mik-1-timing-reference-phase.html#post1419514


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## vidareje

Thanks a lot The latest beta version(7) of REW has implemented exactly what I needed. I can generate a testsweep with a time reference and store it on my music server. I can then play the file though my Squeezebox with the correction file installed in the Inquz convolver. The measure procedure waits for the time reference tone before it starts recording. It worked like a charm


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## StanDingwave

I am an "old hand" with REW but quite new with using JRiver as a player and active three way crossover. Using WDM as the device for REW works, but all my sweeps are choppy and the measurements "may be corrupted". I made a few trials of the WAV method described above, and it does work. In my case, I tell REW to output to an unconnected port so it's happy  I have to manually start the sweep WAV in JRiver; it takes a bit of luck to get the timing right, but it will read a good sweep.


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