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Discussion Starter · #1 · (Edited)
I noticed that when I go to measure, the more sweeps I have REW run the crazier my FR curve gets. I was under the impression that running more sweeps basically just gives you an average of the readings so that if there is some kind of noise during one of the sweeps it won't affect the final results as much. However, I am getting huge changes.

The top purple one is one sweep, green is two sweeps, and the wacky purple one is 4 sweeps. Ive tried it a few times moving the mic around and can replicate those dips time after time just by changing the number of sweeps


Also, I noticed that when I switched from using a mic I had laying around to the UMIK-1 my impulse response changed significantly. I wasn't getting any spikes before in the negative time portion and now I am. I don't really understand impulse response(although Ive been searching and trying my best to learn) but I read somewhere that having those spikes before the large spike is bad. Is this normal? Maybe my new mic is better than my old one so it is detecting something that was getting covered up previously?


I don't have a picture of how it looked like before, but it was basically the same without those two little spikes at the begning.
 

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Some setups do not properly align multiple sweeps (can see that from multiple closely spaced peaks in the impulse response), possibly related to sample rate conversion in the chain somewhere. If the response differs when using multiple sweeps (as in your case) you should stick to single sweeps.

The peaks ahead of the main peak in the impulse response are distortion images. If you are running V5.01 beta you can see the distortion levels on the distortion plot.

For easy comparison of your responses to others you will find on the site it is best to stick to a 60 dB SPL span on your plots (usually 105dB at the top and 45 dB at the bottom). The 'Limits' button above the graph lets you set those values.
 

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Discussion Starter · #3 ·
Some setups do not properly align multiple sweeps (can see that from multiple closely spaced peaks in the impulse response), possibly related to sample rate conversion in the chain somewhere. If the response differs when using multiple sweeps (as in your case) you should stick to single sweeps.

The peaks ahead of the main peak in the impulse response are distortion images. If you are running V5.01 beta you can see the distortion levels on the distortion plot.

For easy comparison of your responses to others you will find on the site it is best to stick to a 60 dB SPL span on your plots (usually 105dB at the top and 45 dB at the bottom). The 'Limits' button above the graph lets you set those values.
Thanks for the reply! Is there a chance that this issue will cause inaccuracies in the FR when running just a single sweep?
 
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