Weird Digital Artifact

C

chflynt

New member
Hi folks. I have an interesting problem that I hope you can help me with. I recorded sound on a video shoot a few days ago. When we got back to the studio, all tracks had this weird, chirpy background noise in them. You can hear it below.

Also, here is the spectral display from Audition of the same clip.
chirpy_spectral.png
You can see the artifact clearly. I have no idea what we did to produce this and I have not been able to reproduce it. My field recording equipment is: Azden MX 100 shotgun mic, feeding into an Azden FMX-42 field mixer, which is hooked up to a Tascam DR-40 digital recorder. I use all high quality XLR cables.

Can you tell me what caused this and how to avoid it in the future?
 
It makes a pretty picture. :)

Was this outdoors/indoors?
Is this amplified to make it audible?

I have no earthly idea what could make a multi-pitch sound like that, but if it's not amplified and it wasn't audible at the site, it has to be in the hardware or processing somewhere...
Four second clip is not much to go by, but it is plainly evident that it's repetitive, so not natural.
 
Set the entire set-up together again and see if it's still making the same noises...if so, change mikes, change recorders, change cables until you find it...
If it's not making that sound still, it had to have something to do with the site. Try recording at that site again and see if you can duplicate.
 
We shot both inside and outside at the location and all clips, no matter the location, have this sound. I have the same set up together now and am using it for another production. And the noise is no longer present. I know it has to be something in the settings of one of my components. But I have tried all kinds of different combinations of settings and cannot reproduce it. I have heard similar artifacts produced when using noise reduction software in post processing. But not that extreme.
 
Only way I could recommend to avoid the problem in the future would be to do random listen checks when you have breaks in the shooting or whatever. Unusable audio when you get back to the studio is too late. Re-doing a few clips on site is much easier than having an entire set ruined. When you hear the noise again (if) you may be able to remember the last change you made and then undo to see if it's the problem...
 
My guess is that the noise is a consequence of an inadvertent feedback loop. It has the sort of sound that you get with extreme noise cancellation.
 
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