Buzzing with CNF Filter

[Drew]

Hi All;
I'm currently working on a problem child record and when running the CNF filter I get a buzz that gets put into the file. This also happens when I just preview the file. I'm using the Normal CNF option as usual. I also ran the filter at different gain levels, thinking the gain might be too low, with no difference.

I did notice there was a post a few days ago about the CNF filter and recording levels, would this have something to do with it?

I did run across this problem awhile back but cannot remember how I solved it accidentally.

Thanks...

Drew

P.S. I just remembered that I did have my cell phone in the studio when I was working, could that have anything to do with it?

[Craig Maier]

I know that some types of cell phones do interfere with audio systems and equipment, including audio preamplifiers and soundcards. My own personal experience is that phones on the Cingular system seem to create the interference whereas those on the Verizon system do not. The reason that I know that is because Ii am on the Cingular system right now and have witnessed this situation. However, when I was on Verizon I never witnessed a problem.

I have heard of that noise being referred to as "Nortel" noise. There is a preset in the preset sharing section of this forum that is designed to get rid of that type of noise from Forensics recordings.

At any rate, if you want, send me a short clip of the wavefile and I will let you know what I think that it is. I am at:

dctools@aol.com

Keep the file to around 10 seconds of audio which includes the problem noise(s).

[Drew]

Thanks, Craig. I'll try to get the file done this weekend and get it to you. BTW- I reran the filter
just now without my phone in the room and got the same result, so it must be something else within the file.

[Craig Maier]

Just to follow up on this - - - the buzz had a fundamental component at 108 Hz with odd and even multiples thereof. I was able to dramatically attenutate it by applying the Harmonic Reject filter in two passes with one doing evens and the other doing odds. The setting for both were 108 Hz and 11 Harmonics.

The source of this noise is more elusive. I believe that it came from a grounding problem between the turntable and the preamplifier. But why 108 Hz? Here is my theory. I think that the turntable may have been a quartz lock type with its own internal servo loop. Thus, the noise frequency of the motor would not necessarily be a harmonic of the AC Line - - - just my theory.

[Drew]

That could be the problem, but, why all of a sudden would it start acting up after a year 1/2 of no issues? And why would I have the problem with BOTH turntables & preamp setups (one is a Numark direct drive turntable with a standard mount, one is an older hitachi with a TP4 mount)? Too many questions.

Also, if it were a grounding issue, wouldn't it show up when I did the initial recording and be there through the previous filter runs?

Craig, (I'm pulling at thin air here), could it be possible that there is a ground issue that is not noticeable until the CNF is run?

[Craig Maier]

The most confusing part is that you do not hear it on the original transfer, just after running the CNF. I know of nothing in the CNF that could introduce that noise. But to proove that, why not try recording a short section of silence from your system. Run the CNF on it and see if that noise appears. That will give us something to go on.

When you record the silence, record it with different setups. One setup could have the preamp disconnected from the soundcard, another with the preamp connected, but the turntable disconnected, another with turntable connected, but not turning, etc.

Maybe the noise source can be determined by this sort of process of elimination.

[Drew]

Okay, I'm finally able to get back to my problem. I was monkeying around with the presets on the CNF filter and wondered if changing the presets around would make a difference? The buzz was not there when I changed to a couple of the presets and ran the preview.

So, I'm wondering if I at some point changed to one of the presets and that became the default? I think it was one of the Edison presets that seemed to create the buzz.

What would the "default" default preset be, the "typical vinyl 33 fingerprint", maybe?

Thoughts????

[Craig Maier]

Are some of the problematic presets using "Overlap" values that are real low (less than 35%?).

[Drew]

I don't recall, but I can take a look tonight. I only changed between the presets, but I did not change any of the preset values themselves. Should that value be above 35%?

[Craig Maier]

For "High - Fidelity" work (non - Forensics) I would recommend that the Overlap % be set above 35%. I usually just leave it at 50%.

[Drew]

So, would changing/lowering the overlap percentage introduce the buzzing I had on the files when I ran the filter?