What's that stuff before T0 in the impulse graph?

[torarnv]

Hey all,

This is probably a very stupid question, but what is all that information before T0/Ref in the impulse response graph?

My basic understanding of an impulse response is that it's a short burst of sound that has the same energy at all frequencies, like a gunshot e.g. And based on how that spreads in the room we can see how the room behaves.

But doesn't that mean that the sound is emitted from the speaker at time X, and the direct sound reaches the microphone at time Y, which we then name T0? What sound reaches the microphone before T0? The noise floor? But why does it rise towards T0 then?

Thanks for any clarifications on this!

(Btw, loving the new REW UI!)

 

[John Mulcahy]

The help explains impulse responses: https://www.roomeqwizard.com/help/help_en-GB/html/impulseresponse.html#top

The stuff before the peak is mostly noise, the lead up to the peak depends on the device and measurement bandwidth.

 

[torarnv]

Ah, thank you, that manual is very helpful! I was looking at the "Impulse Graph" page but didn't make the connection to click the link to "impulse response"

If it's noise I guess I can safely ignore it when analyzing room reflections and the like, since those should presumably all come after T0. Out of curiosity, is it noise in the microphone/recording stage? Or noise that the speaker or output stage produces the few milliseconds before it's going to produce the sound that we're actually trying to play (the impulse)?

 

[John Mulcahy]

It is a combination of noise in the capture path and the acoustic background noise.

 

[torarnv]

Thanks John! Fun to learn about all these things!