Sweeps report approx 3000ppm timing errors

[Tony Walters]

Hello,

When performing sweeps at 512k samples and 1m samples as examples, the measurment reports large timing errors and suggests verifying that sweeps and generated sweep file are at same rate (they are) and to look for dropouts.
This is the first time this error has surfaced in over 2 years of using REW, I have current product release on one laptop, and Beta4 installed on another. Same errors. have tried different volume levels for the sweeps. Same errors. I use the generator to create the measurement sweep .wav files with timing chirp, and then that gets copied over to Volumio folder and plays from there.

Also, the impulse reponse is very strange, maybe not surprising. Occasionaly, it also reports that distortion is abnormally high, but not all the time. Otherwise, the sweep response looks normal.

I replaced the USB cable for the UMIK microphone, same error.

My setup is RPI4 Volumio streamer, with FusionDSP, USB out to RME-ADI 2 DAC, feeding preamp to active crossover, feeding power amp. 2.1 system crossed at 50hz, low to sub, high to main speakers. Same error whether FusionDSP is enabled or not.

I tend to think the mic is ok (and the response file for UMIK is loaded). Maybe it could be the problem?

I posted on minidsp forum in the UMIK section and no responses.

I appreciate if anyone has seen this before, and how to resolve it.

Cheers,
Tonyw

 

[John Mulcahy]

You can check for dropouts by opening the Captured graph after making a measurement, it shows the raw sweep signal obtained from the mic. Look for flat spots or discontinuities. The graph is only for the last measurement made.

 

[Tony Walters]

You can check for dropouts by opening the Captured graph after making a measurement, it shows the raw sweep signal obtained from the mic. Look for flat spots or discontinuities. The graph is only for the last measurement made.

Hello John. Here is what the graph shows. I'm inferring that the signal level is really low but what could be causing it? I'm using all the same levels as before. At this level, I'm surprised it can generate a measurement result.

 

[John Mulcahy]

You can hide the Sweep trace and just look at the Captured trace. Zoom in on the Y axis to make it easier to see the signal and look through it to see if anything stands out. The level is OK. If you don't see anything attach the mdat file for a measurement that generates the error.

 

[Tony Walters]

Thank you John. In the meantime my sub plate amp failed and waiting for replacement. It did, however, give me a chance to re-run sweeps without sub. I took out the active crossover and ran the attached sweeps. No change, the timing errors seem to have stabilized around 1000-1100ppm.

 

[John Mulcahy]

the timing errors seem to have stabilized around 1000-1100ppm

Those do look like the corrections needed to get something resembling the one good measurement, number 5, which was 28.8 ppm. Seems like something has a clock that's a long way off, most of the time. I can widen the limits to allow adjustments that large to be applied, but that's a very big shift. What's the UMIK connected to? It gets its clock from the USB host.

 

[Tony Walters]

My laptop has the new USB connector while the UMIK has the full size USB so I have a USB hub Hyper which has a number of ports including full size USB. I am not using any of the other ports. However, this was failing on my other laptop with a full size USB thats why I dont suspect the hub.
The timing error is now always 1049ppm now. I do get the proper looking impulses on the overlays now,
I do notice that on the latest beta that the error message says that it could be reflections from objects in the path to the microphone. I havent seen issues before, but their is a coffee table. I can remove that and see if it changes anything. I suspect it wont because objects on the table are always changing yet the error is now the same each time - but I will do it and report back.

'best
Tony

 

[John Mulcahy]

If you have a stable difference it won't be due to reflections.