Problem with offline measurement

[Keith_W]

Hi John, I went to my friend's place yesterday to take some measurements of his listening room. I brought along my laptop, my Focusrite 2i2, and an XLR microphone. Unfortunately, I only have XLR outputs, and he does not have XLR inputs on his AVR. So I decided to take an offline measurement.

There were more issues with the offline measurement. My ancient Focusrite can only use a 48kHz sampling rate, and his ancient AVR can only use 44.1kHz FLAC files. So I generated a 44.1kHz 1M sweep with timing chirp, converted it to FLAC using JRiver and gave it to him, and a 48kHz 1M sweep with timing chirp which I loaded into REW.

This was the result (MDAT uploaded):

Clearly this was a nonsense measurement. Nothing I tried could remedy the situation. I don't think it was feedback from the microphone either.

Just FYI the same measurement setup was able to successfully take measurements a week previously, although that time I did not have to take an offline measurement since the other system was able to accept XLR inputs.

I am wondering whether a 44.1kHz 1M playback and a 48kHz 1M reference are substantially different enough to produce this kind of result.

 

[John Mulcahy]

A nonsense result would be expected since part of the system is running approx10% slower than expected and it's playing the wrong signal, but the repetitions suggest there was also some other factor involved. Not sure how an AVR could fail to handle 48 kHz data, how would it play a DVD? That aside, might have had better luck using the Java drivers, setting REW to 44.1 kHz and letting the OS resample from 48k.

 

[Keith_W]

Thanks for the quick response, John. In hindsight, it may have been possible that I tried to play a 48kHz .WAV file on his AVR and failed. So I tried a 44.1kHz FLAC and it worked, so I left it at that.

I don't know what is causing the repetitions. I usually bring my RME along when I take measurements, but that RME is usually plumbed into my system. I prefer the RME is because I can watch what is happening in the RME's mixer, rather than watching flickering front panel lights on the Focusrite. I am too lazy to unplug it, so I have started using my old Focusrite. In any case i'll need to go back, so i'll try to find out what went wrong.