Q to John - How does the sweep work?

[steve138]

Question for John
(Sorry had to repost ad I couldn’t fix the mistyped title On first version)
this might be a dumb question but when setting a gated time window on a sweep to avoid room reflections how does it avoid taking into account the late arriving reflections that are still coming back to the mic while the sweep itself is still running?
As I couldn’t get my REW waterfall plots to look like Danny Richies spectral decays using CLIO I got hold of a used CLIO Pocket which I just started to evaluate. CLIO uses more of a fast burst rather than a longer sweep like REW (what they call log chirp). My first measurement looks good but their software is crap and doesn’t hold a candle to your majestic achievement. Thanks for all you’ve done for the community

 

[steve138]

Oh crap and I mistyped again!

 

[dcibel]

I'd answer, but I'm not John, or a John.

 

[John Mulcahy]

Windowing is applied to the impulse response derived from the sweep, not to the sweep capture itself.

 

[steve138]

Windowing is applied to the impulse response derived from the sweep, not to the sweep capture itself.

Cheers John, but how are the reflections excluded, or how is the impulse derived from the sweep so the reflections can be excluded? Is there a description of how all this works? Is this what the FFT is doing

 

[John Mulcahy]

Google "Transfer-Function Measurement with Sweeps DIRECTOR’S CUT INCLUDING PREVIOUSLY UNRELEASED MATERIAL"