Mysterious Crackly Popping Noise Occurs Like 1 in 25 takes

Ok, I have been recording for several months now with a PreSonus Audiobox iTwo connected to my iMac, and a Rode NT-1 mic. But I was experiencing generally low input levels and this crazy mysterious crackling noise which would just out of the blue appear on one recording and be gone on the next 20 or so recordings, and then for no apparent reason appear again, and disappear on subsequent recordings with no change in setup. It’s like a phantom menace that I can’t explain or fix.

Now, in the meantime, my husband bought me a Wharfedale Pro Connect 1202FX/USB mixer to sort of replace the PreSonus because we thought there must be something wrong with it not giving me enough umph… and because of this weird occassional crackling. When I was recording with the Wharfedale instead of the Presonus (for the last 2 weeks) we never heard the crackle, not once. But we did have a lot of presumed self-noise through the mixer that we’ve been battling, and through another forum thread it was suggested that it might be something to do with the USB. So he had a bright idea and removed the USB out from the mixer board, and instead used a headphone plug from the Line Out and ran it into the Presonus input, and and we turned off the phantom power on the Presonus, and it seemed to get rid of the large amount of self-noise from the mixer. All was good, I’ve been recording today and liking the general sound (but aware it needs some tweaking).

Then, out of nowhere, the dreaded crackle returned on this take. Now, you won’t hear it at the beginning, it seems to build up more and more along the duration of the recording, and you can see it distinctly in the waveform especially at the end of phrases before the silence breaks. Does anyone know what this is or have you heard something like it before? I was starting to question whether my Presonus might be defective but since the crackle has suddenly returned after adding the PreSonus back into our mix, I am thinking now it must be the Presonus… unless those of you who are more experienced can shed some light on what you are hearing in my sample?

Thanks!
Barbara

https://www.dropbox.com/s/716pnkbvemoc5ay/crackly%20mystery%20noise.wav?dl=0

I don’t know we have any firm idea what causes that, but it seems to respond to different settings in:

Audacity > Preferences > Recording > Audio to Buffer.

My personal recommendation is to change that setting to try to make the problem worse. Once you have a handle on what it’s doing, you have a good idea how to get rid of it. If you only make one simple change and the crackling seems to go away, you never know what you really did or whether it’s waiting for you later down a dark alley.

Koz