Can I use a different test tone source?

[Michael Brinkman]

I have Omni Mic 2 software which comes with a Cd with a variety of test tones. I like using the short wideband bursts to help cut down on room reflections. Is there a way to bypass the setup where which requires the built in audio signal generator?

 

[John Mulcahy]

I'm not really sure what you are referring to or what kind of measurement you wish to make. Signals from that CD are unlikely to be useful with REW, they might have some application if you are using the RTA. The length of the test signal has little to do with room reflections. Reflections are generally gated out of the measured response using the impulse response windows.

 

[craig john]

Reflections are generally gated out of the measured response using the impulse response windows.

Could you please explain how this ^^^ is done? Thanks!!!

 

[John Mulcahy]

Adjusting the windows is explained here. Reflections show up as spikes in the impulse response (more easily seen when using the dBFS view). In a typical room they will start within a few ms of the initial peak. They show the arrival of sounds that have bounced off the room's surfaces, so have travelled further than the direct sound to the mic (which corresponds to the initial peak). If a reflection travels an extra metre compared to the direct path the spike will be 2.9 ms after the initial peak, the time sound takes to travel 1 metre. Setting the right hand window just before that spike (with the window reference time set to the IR peak) excludes it from the response, but the trade-off is a loss of frequency resolution. A right hand window of 2.8 ms would mean a frequency resolution of 1/0.0028 = 357 Hz, so low frequency information is lost and the rest of the response lacks resolution.

 

[craig john]

Thank you again for the explanation! Much appreciated.

Craig