REW output problems

[butcher_1985]

Hello all! I began trying to use REW today and could really use some help. I've spent several hours looking for the answer to my problem on various forums, but I'm afraid I couldn't find the answer, so I'm hoping you may be able to help me out!

I'm trying to set everything up in the Soundcard tab of the Preferences window. My soundcard is my Focusrite 18i20, which is also where my mic is plugged in. So I set my 'output device' and 'input device' to my 18i20 as suggested, leave Java as the driver, and leave the sample rate at 48kHz. Irrespective of what I choose for my 'output' or 'input', when I hit the 'check levels' button to see if everything is working OK, I get the following error pop up:

'The soundcard did not provide any input data, please check that it is connected'.

After experimenting with the ASIO driver setting, I have been able to generate an output from one of my speakers as normal, and have managed to follow the process through to getting a frequency response chart of my room. But unfortunately only one speaker works at a time - I cannot find how to get both working simultaneously. I saw on a forum that I might be able to do this by setting the 'output' to one of my speakers and setting the 'timing reference output' to the other speaker, but unfortunately I could only manage to get sound coming out of the 'output' speaker.

Do you think you might be able to help with my problem? Any help would be really gratefully received! If it helps, I'm using Windows 7 64 bit.

Thanks very much!
Andrew

 

[John Mulcahy]

On the Measure dialog there is a second output selector below the main Output selector, to enable it check the box next to it then choose your second output channel from there. There aren't many circumstances where it is useful to drive more than 1 speaker at a time though.

 

[Matthew J Poes]

On the Measure dialog there is a second output selector below the main Output selector, to enable it check the box next to it then choose your second output channel from there. There aren't many circumstances where it is useful to drive more than 1 speaker at a time though.

Please heed johns advice. With the exception of low frequency modal analysis you should only be using one speaker at a time.

Speaker as timing reference is just a workaround to allow a constant timing reference between measurements when no loopback is connected. It is not a means to measure multiple speakers.

 

[butcher_1985]

Thank you both very much for such quick replies! I will certainly take your advice. That said, I am interested to understand why it is better to run tests using only one speaker instead of both. Our normal listening experience is with both speakers playing, so intuitively I would have guessed that we would want to test the characteristics of our rooms when both speakers are playing, rather than just one? Would you be able to explain to me at all, or perhaps point me to a helpful document for me to research further?

Thank you very much again
Andrew

 

[Matthew J Poes]

The basic reason is it doesn’t provide useful information. When you measure two speakers they are coherent, this will cause comb filtering due to inter-channel delay. It’s just a measuring artifact of sorts.

By measuring individual speakers you get the sound without this artifact and can better see what is going on.

The exception to this is below the rooms transition frequency. At low frequencies the room response is steady state. All speakers contribute to the low frequency response and in fact there is benefit to having the multiple Lf sources. As such as low frequencies it’s fine to measure all LF sources together. At higher frequencies it isn’t meaningful.