Loopback-time align

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
Hi.

I am trying to use the loopback feature to time align my speakers and subs. The problem I was/am having is no consistency in adjusted measurements. So I decided to run several sweeps using the same speaker without adjusting the speaker time delay. Using the Impulse/overlay, this showed the sweeps moved each time on there own, which kind of explains why I couldn't get them to align.

I am using REW V5.20. I have set 'use loopback as timing reference' in the preferences/analysis. I am using a USBPre 1.5 pre amp. I have a loopback cable installed in this (i've used this set up a few years ago to time align using REW)

Is there something i'm missing here that's causing this error? Attached shows 3 impulse's. Each time it moved slightly
loopback.jpg
?


Edit. Just run some more sweeps and now I cannot alter the delay. Every sweep aligns with each other. As if loopback is switched off
 

Attachments

  • analysis.PNG
    analysis.PNG
    30.1 KB · Views: 77
Last edited:

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
I have just tried using REW on a different PC. I seem to be getting similar results. Using loopback the measurements are jumping around. I can run sweep after sweep without adjusting anything and the impulse alters each time.
 

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
7,212
Are you using the USB Pre for output and input? Can you attach an mdat file with some example measurements?
 

AudiocRaver

Senior Reviewer
Staff member
Joined
Nov 21, 2016
Messages
974
Location
North Carolina, USA
More  
Preamp, Processor or Receiver
Onkyo TX-SR705 Receiver
Main Amp
Crown XLS 1502 DriveCore-2 (x2 as monoblock)
Additional Amp
Behringer A500 Reference Power Amplifier
Front Speakers
MartinLogan Electromotion ESL Electrostatic (x2)
Center Channel Speaker
Phantom Center
Surround Speakers
NSM Audio Model 5 2-Way (x2)
Subwoofers
JBL ES150P Powered Subwoofer (x2)
This looks like results I have seen using the HDMI / AVR / amp / speakers path for output and an analog (not USB) mic / USB audio interface for input path. The loopback at the audio interface can not resolve minute timing differences (from sweep to sweep) between the HDMI path and the audio interface path.

My solution is to change the loopback path and connect a line level output from the AVR to the loopback input of the audio interface. That puts the entire computer and the AVR inside the loop. The timing uncertainty will disappear.

The difficulty though, is that the line output you choose must be active for every measurement sweep, but the speaker normally associated with it must be silent. I disconnect my center channel speaker during these timing-critical measurements and use the center channel line output for the loopback source. Then reconnect the center channel speaker for running Dirac Live calibration (if appropriate) and regular listening. A surround speaker line output can be used if the center channel is inconvenient for some reason.

John might have a better answer than this. If so, I defer to his expertise.

** Edited the third paragraph.
 
Last edited:

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
Are you using the USB Pre for output and input? Can you attach an mdat file with some example measurements?


Hi John.

Yes, using USBPre for output and input. Connections are as follows:

Microphone to Mic1.
PC audio output left to Mic 2 'loopback'
PC audio output right to processor analog in.
PC USB to Pre USB port.

The file I've attached, the first 5 measurement are from one sub, the last 3 from another Sub. The results never moved around this time, they've all lined up. But I am unable to adjust these using my processors 'speaker delay' settings this time. So somethings being a bit funky...

I have previously 'successfully' used REW to time align with my setup on many occasions using the same kit, albeit along time ago.

Thanks for you input AudioRaver. Will see what John comes back with first....
 

Attachments

  • USBPre.PNG
    USBPre.PNG
    18.6 KB · Views: 93
  • REW.mdat
    3 MB · Views: 26

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
Also attached REW mdat from my other PC. These results have moved around on there own.
 

Attachments

  • REW impulse.mdat
    1.1 MB · Views: 13

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
7,212
REW.mdat was measured with REW V5.10, REW impulse.mdat with REW V5.20 beta 5. The last 3 measurements in REW.mdat have a big delay, almost 800 ms, so something is a bit odd there also. Don't see any particular reason why the setup shouldn't work, but REW doesn't keep a record of the level seen on the loopback connection so worth making sure the level on that mic 2 input isn't too low or too high. I suppose there is a chance the processor is doing something strange, since it is out of the feedback loop. Could try taking both channels to the processor and bringing one back as the reference, along the lines AudiocRaver suggested, to try and eliminate that possibility.
 

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
This looks like results I have seen using the HDMI / AVR / amp / speakers path for output and an analog (not USB) mic / USB audio interface for input path. The loopback at the audio interface can not resolve minute timing differences (from sweep to sweep) between the HDMI path and the audio interface path.

My solution is to change the loopback path and connect a line level output from the AVR to the loopback input of the audio interface. That puts the entire computer and the AVR inside the loop. The timing uncertainty will disappear.

The difficulty though, is that the line output you choose must be active for every measurement sweep, but the speaker normally associated with it must be silent. I disconnect my center channel speaker during these timing-critical measurements and use the center channel line output for the loopback source. Then reconnect the center channel speaker for running Dirac Live calibration (if appropriate) and regular listening. A surround speaker line output can be used if the center channel is inconvenient for some reason.

John might have a better answer than this. If so, I defer to his expertise.

** Edited the third paragraph.

You little beauty AudiocRaver. This appears to be working. Thank you :T
 

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
As my sub's are placed front and back of the room the phase is out 'looking at these impulse responses attached'. Should I reverse the polarity of the rear sub so it's impulse matches the front?
 

Attachments

  • one.jpg
    one.jpg
    30.5 KB · Views: 38
  • two.jpg
    two.jpg
    29.2 KB · Views: 37

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
7,212
Probably, but it is difficult to say whether that will make things better or not. Easiest is to make measurements of the response inverted and not to see what looks best. You could also try the Multi Sub Optimizer to see what it suggests.
 

jtalden

Senior Member
Joined
May 22, 2017
Messages
887
Location
Arizona, USA
More  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
VTV 6 chnl NC252MP P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
Wull, If you want to post an .mdat file using
loopback timing and
containing the 2 sub measurements, I can confirm the polarity and advise timing between them using the phase relationship of the direct sound from the speakers.
If you include a left and right main speaker measurement also I can comment on the timing between the 2 subs and the mains as well.
Per John's comments, MSO or just setting distances per impulse peaks and testing
polarity
for the best SPL should work just as well.
 

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
That's very kind of you jtalden. I am just waiting on 2 FI IB318's to be delivered. As soon as I have these installed/up and running I will report back...
 

jtalden

Senior Member
Joined
May 22, 2017
Messages
887
Location
Arizona, USA
More  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
VTV 6 chnl NC252MP P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
If you include the main speakers then all measurements need to taken with a full range sweep 20-20k; even for the subs. The XO's all need to be active also; this includes the subs, i.e., if there is a 80Hz XO in an AVR then it needs to be active when the sub is measured. One way to do that is to measure using the left channel with the left main speaker disabled. That way the sub measurement includes the XO effect on the redirected bass.
redirected bass.

These are the key points if you include the mains. I can provide a more detailed description of the setup/measurements if you like.

If you just want to time the 2 subs then it doesn't matter if the AVR XO is active, or if the measurements are full range.
 

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
OK. Well I will have to see what I can do. My processor doesn’t allow for XO’s, I use jRiver for this. Now I know presently (after days of trying) I can’t loop back through jRiver. But I should be able to run REW sweeps through it, which would include the XO.

Thanks
 

jtalden

Senior Member
Joined
May 22, 2017
Messages
887
Location
Arizona, USA
More  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
VTV 6 chnl NC252MP P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
The newer versions of jRiver allows loopback to work per some comments I have seen posted. You may want to check details with other jRiver users. An alternative is to use REW acoustic timing instead of REW loopback timing. That way works well for any setup. We just need to use the same reference channel for each measurement.
 

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
Sorry, It’s not jRiver that’s stopping me using loop back. I use a Lynx AES16e . Its currently not ASIO multi-client. Lynx are working on a new driver to fix this.

I shall have a look at REW acoustic timing....
 

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
I have run a few REW sweeps with my subs. What I have in my room is a 'front of room ceiling mounted IB manifold'. And I have a 'rear of room ceiling mounted IB manifold'. Also, I use 2 x 15" DIY ported subs. These ported sub's don't go very low at all, but they give me upper 'chest slam' frequencies. I have attached an .mdat file so you can see what is going on. Until today I have had both ported sub's up front beside my main speakers..It was using the REW sim that made me look at moving one of them behind my sofa. It's all probably a little premature as I am waiting on 2 more IB318's for the front IB manifold, which I know wont change things greatly, but all the same. All sub's levels where set to 82dB.

Loaded a Subs and IB.mdat This file contains a REW sweep with both 15" subs back where they have always been. At the front of my room
 

Attachments

  • SUBS REW.mdat
    3.2 MB · Views: 16
  • subs and IB.mdat
    370.6 KB · Views: 15
Last edited:

jtalden

Senior Member
Joined
May 22, 2017
Messages
887
Location
Arizona, USA
More  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
VTV 6 chnl NC252MP P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
I used the 4 sub measurements (1-4) in SUBS REW.mdat for analysis. I assumed there will be no XO applied within the group of 4. They would have an XO applied to this entire sub group when the mains are added.

The delay timing was
adjusted
using REW to get the best direct sound phase tracking. The delay timing change was:

F-IB 0 ms

R-IB -1 ms (trivial)

F-15 -12 ms

R-15 -12 ms
The polarity of the F-IB and R-IB was also changed.

The resulting impact to SPL is trivial except for the range 70-110 Hz where there is significantly more SPL support with the change. Below are some charts to show the impact of the change. I also attached an mdat file showing the adjusted timing and summation response.
1 SPL Timed.jpg
2 SPL All.jpg
3 Phase Timed.jpg
4 Phase All.jpg



 

Attachments

  • ja Subs REW.mdat
    1.8 MB · Views: 17

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
Thank you so much jtaden. Looks impressive. Hopefully I will be able to XO around 100 Hz.

Sorry I should have said. Yes I never used a XO. I had a play trying to get this to work. I have to swap from ASIO to Java, then use the jRiver 'wdm' driver. It worked in a fashion. However, using this method I'm really not sure how I can get a sweep to play through jRiver showing both mains and sub's at the same time when the XO is engaged. I need more time to look into this...

"F-IB 0 ms

R-IB -1 ms (trivial)

F-15 -12 ms

R-15 -12 ms
The polarity of the F-IB and R-IB was also changed"

Are those 'negative' -ms changes. And reversed polarity on both IB's?

It will be interesting to see what the 2 new drivers bring once installed. This should give me more spl sub bass level I would imagine.

Thanks again for you time :T
 
Last edited:

jtalden

Senior Member
Joined
May 22, 2017
Messages
887
Location
Arizona, USA
More  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
VTV 6 chnl NC252MP P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
I would have expected that aligning subs with a different low end response and/or with different rolloff rates can be much more troublesome than using identical subs. I have no practical experience prior to this however. In this case they played together very well; better than I expected.
Yes, I reversed the polarity on the 2 IB's. I could have reversed the polarity on the 2 15's instead. Either way all subs would then have the same polarity. The summed polarity is positive with the IB's reversed. It would have been negative if the 2 15's had been reversed . There is no right polarity, or wrong polarity, until the mains polarity is considered. When the mains are considered then the sub group polarity can be decided based on our objective. I like to achieve close phase tracking through as much of the XO range as possible. Excellent result are also possible allowing a phase crossing at the XO frequency and having more diversion of phase tracking across the range. There is a tradeoff of pros/cons making it debatable as to which way is better. It's an issue because many users report they can clearly hear the differences in the bass sound with the 2 approaches.
I can't help much with your continuing issue with jRiver setup as I tend to get confused trying to troubleshoot systems I don't use. Did you find a 'how too setup' yet for jRiver users? If you post; problem description, equipment used and screenshots of your REW settings and I am sure this can be sorted out by someone here. Have you created the 20-20k wav file with the acoustic reference timing? Does it play through jRiver? Do your hear the chirp in the reference channel? Do you know how to make the settings in REW to have it wait for the chirp sound before starting the capture? Is the only problem how to measure mains, subs and both together? Can't you just disconnect the sub or main or leave both connected to make the 3 measurements? That way the XO is active for all 3 measurements as needed. We just need more info to be helpful.
It takes me significant time to analyze and writeup each scenario. There are a very large number of possibilities of XO settings, sub/mains positions, listening position and other parameters that impact the results. I ask that you minimize the number of these that we do.
 

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
Thanks again for that explanation. And boy is this digging deeper than I've ever REW dug before!

Yes I have managed to get REW to play L&R and sub channels through jRiver with bass management, and this includes the acoustic ref timing timing. And yes there was a chirp sound just before an acoustic ref timing timing measurement was taken.

Do you know how to make the settings in REW to have it wait for the chirp sound before starting the capture? Do you mean the tick box 'highlighted attached pic'?

I have not created a wav file (do you not mean mdat file?). I will wait for the last 2 IB drivers to be delivered/installed before I post anymore measurements. This may be next week, if not then mid March as I'm away snowboarding at the start of March.

Sorry I didn't realise the time involved when working this out. I will try and keep these to a minimum. My only one request is I would like to take 2 REW sweeps positions for the back of room 15 sub. This sub normally lives up front, more or less next to the other 15. It was REW sim that gave me the idea of see how things looked with it positioned behind my sofa. I'm just a little worried it may be to close to the seating position?
.
 

Attachments

  • time.PNG
    time.PNG
    18.5 KB · Views: 41

jtalden

Senior Member
Joined
May 22, 2017
Messages
887
Location
Arizona, USA
More  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
VTV 6 chnl NC252MP P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
To use acoustic timing in your case:
> Make a wav file using the REW signal generator. The latest beta version looks as shown below. The earlier REW versions look differently, but there is the same capability. This example creates the measurement sweep on the right channel (mic on right input) and places the timing signal on the left channel. You can change this to meet your needs.
> Yes, check the wait for timing signal box you highlighted, select the right channel for the measurement and the left for the timing ref output (matching the created wave file).
> To prevent REW from playing the sweeps directly to the processor set REW 'level' and timing ref level' to -90dB as shown.
Be sure the sample rate, FTT length, and sweep range matches the settings you used in creating the wav file.
> Then 'start measure'. REW will start the measurement process, but then pause waiting for you to play the wav file in jRiver. When REW/Mic detects the reference chirp it will finish the measure process.
SweepFile.JPG

Measure.JPG
 

Wull

Registered
Thread Starter
Joined
Apr 26, 2018
Messages
52
Hoping to have some new measurement to post in the next day or so jtalden. The new IB drivers are installed. I also ended up getting a UMIK-1 mic and a minidsp HD. The UMIK has made it a lot easier 'for me' to run REW through jRiver using the acoustic timing. I'm hoping the minidsp will help creating a house curve. Will see?

I spent a couple of hours yesterday moving the DIY 15" sub's about. I think I have found there best position now. Just need the house to myself and I am good to go......
 

jtalden

Senior Member
Joined
May 22, 2017
Messages
887
Location
Arizona, USA
More  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
VTV 6 chnl NC252MP P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
I'll watch for it.
 
Top Bottom