VO-BB - 19 YEARS OLD!

FinMac · Posted: Tue May 31, 2016 2:36 am Post subject: Room for improvement ?

Been in the process of setting up a new recording space. It is a place where I can stand up, stretch my arms and not bump into anything Smile

Some of the inspiration came from Lance Blair's Blog on the Studio/Office, and some from watching Rick Riley build out his amazing studio. Thanks guys!

The project is perhaps 95% complete and the room was going through some testing, when I noticed a strange problem.

After some initial recordings that sounded good, with a low noise floor, came a series of recordings with a strange bump in the noise floor in the 15 - 16 kHz range. Anyone with Adobe Audition will see this if you download the file and check out the noise floor.

Tried everything to isolate the problem. Changed mics, cables, AD converters, micpres, recorded with the monitor off, etc., but to no avail.

Then something struck me. We installed some solar panels and there is an inverter downstairs which makes noise as the sun hits the panels. Sure enough, when I record early in the morning, before the sun hits our roof, there is no bump in the noise floor. But after the sun begins to do it's work, the bump in the noise floor appears!

Somehow this noise gets into the electricity and effects the audio. I have some high quality cables, and even a Furman power conditioner, yet this bump in the noise floor shows up.

2 questions...

1. Anyone have a clue how to overcome this problem ?

2. (After listening to the audio sample) Does it really matter ?

Thanks for your time and thoughts!

https://www.dropbox.com/s/o7kelngyyeav1af/Scott%20McDonald%2016%20kHz%20bump%20in%20noise%20floor.wav?dl=0
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heyguido · Posted: Tue May 31, 2016 5:37 am Post subject:

I'd like to challenge the assumption that somehow this noise is getting into the chain through the electricity....

Try recording without the mic. I suspect this noise is actually noise emitted by the inverter in the audio spectrum, and not injected electronically. Such sounds are tough to eliminate through sound dampening, and usually require more robust isolation.... Or perhaps, a simple notch filter in EQ.
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FinMac · Posted: Tue May 31, 2016 6:28 am Post subject: Thanks Don

Thanks Don for the reply.

Recorded something with the micpre on but without a mic, using a Vovox shielded cable. No noise problem.

Then recorded it with the mic, and Voilà, the noise returns.

But a recording in the smaller space, with a different micpre and mic, no noise.

It is a bump from about 15000 to 17000 Hz. It will take some work to remove it with a notch filter.

Does it cause problems with the audio or does the audio sound OK anyway ?
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"If you want to get to the top, you have to get off your bottom". (Unknown)

Jason Huggins · Posted: Tue May 31, 2016 9:46 am Post subject:

It is definitely a solid tone at 16k. Can you hear it when you stand next to the inverter? I would also suspect that the inverter is causing actual noise. Are you young enough to be able to hear that tone? I personally can only hear the tone when I normalize the audio, but someone with older ears may not hear it a single bit.

Targeted noise reduction in AA will pull it out or a notch filter with a little bit wider Q at around 15750 Hz would bring it down (not using the notch filter plugin but using the Parametric EQ plugin with a Q of around 25. The EQ will have to be at like 10 or more dB in reduction though so it will mess with the audio more than the noise reduction. If you try the noise reduction, select just a portion of the visible noise in Spectral View with the rectangle selection tool and use that as your noise print.

Also if it is coming through the power then I would think that if you removed the power conditioner it might be more intense. I'm betting if you put your ear up to the inverter it will be the culprit. I'd guess that the reason you don't hear it in the other location is because it is just more effectively isolated from the tone.

All that said, I can't hear it unless I normalize the silence which is raising the gain by like 50 or 60dB. No one without throwing the audio on a spectrum analyzer or looking at a spectral display will ever see or hear it (me thinks).

Overall I think the room sounds pretty good.

FinMac · Posted: Tue May 31, 2016 10:17 am Post subject: Thanks Jason

Thanks Jason for sharing your thoughts and insight about what options there are in AA. Appreciate your help on that area.

Yes, the noise is quite strong downstairs that even my more mature ears can hear the inverter. I might be hearing a lower tone than 16kHz. The inverter never became a problem until setting up the new space, and recording later in the morning.

In the small recording space I am much closer to the inverter so I wonder from where the noise is getting to the mic in the new space. Is it just vibrating through the walls and the floor ? would it help to put anything on the wall near the inverter, or on the floor of the big space ?

Thanks also for the encouragement about how the room itself is sounding Smile

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www.scottsvoiceover.com - An American voice in Finland

"If you want to get to the top, you have to get off your bottom". (Unknown)

Jason Huggins · Posted: Tue May 31, 2016 12:52 pm Post subject:

Hard to say without being there. Can you hear the inverter if you press your ear to the walls or floor? I personally wouldn't expect 16k to be traveling far...but I'm sure stranger things have happened. Your ears are going to be the most valuable troubleshooting tool for this one.

If it's vibration through the house maybe you could 'float' the inverter so it doesn't transfer.

vkuehn · Posted: Tue May 31, 2016 1:46 pm Post subject:

heyguido · Posted: Wed Jun 01, 2016 7:58 am Post subject:

Jason's right. Kinda tough to play long distance detective with no knowledge of the layout or construction of your home.

A few thoughts, however. Low frequency vibrations are more likely to be transmitted by the structure of the house. The Rumble of a ceiling fan, for example, can be carried by joists and walls throughout the house.

High frequencies, however, are sneaky little bastards. They like cracks and crevices. They sneak in under doors and around windows... And through ventilation shafts. They bounce and ping, til they arrive at the highly sensitive diaphragm of your condenser mic.

Since you've already identified the source, your best move is to try to stop it as close to the source as possible. Perhaps an insulated enclosure to surround the inverter might be helpful in mitigating the offending squeal. Might make things a little more pleasant around the house, as well. Inoccent

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Don Brookshire
"Wait.... They wanna PAY me for this?"

vkuehn · Posted: Wed Jun 01, 2016 8:57 am Post subject:

Maybe this is the time to implement my favorite little junk-drawer test device. Take and XLR plug and solder a resistor, 150 to 250 ohms usually works well. Across pins 2 and 3. Unplug the mic, plug in the dummy test plug device. If your mic is actually picking up audio, the dummy plug delivers NO AUDIO and the noise will not be there.

If with the dummy plug in place you have 16 khz noise, then it is leaking through the wiring and the power conditioner.The Dummy-plug is indeed dumb. It will NOT tell you how to FIX the problem, but it might help you know what to attack next.

FinMac · Posted: Wed Jun 01, 2016 9:06 am Post subject: Thanks guys

Thanks guys for the suggestions.

Funny thing, this morning I did one recording at about 8:36 AM, and the noise floor was amazingly low. Did a second recording about 10 minutes later and there was the noise.

Went downstairs to check out the inverter and it was producing electricity, but very little, and the noise from the inverter was quite low. Hard to believe the mic could pick it up.

May borrow my wife's Fetascope, a clay device used in Africa to listen to the Fetus/baby in the womb. Either that or a real stethoscope !

We have a freezer in the upstairs hallway which makes noise, but I do not hear it through the 2 doors and walls, so it would be surprising to be able to hear the inverter through the air. It must come through the wall it is mounted on.

This is a tough nut to crack, but it will crack. Thanks again for the helpful thoughts and suggestions.
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www.scottsvoiceover.com - An American voice in Finland

"If you want to get to the top, you have to get off your bottom". (Unknown)

Lance Blair · M&M Joined: 03 Jun 2007 Posts: 2279 Location: Atlanta

Do you hear this noise all the time?

It's a repetitive click. I hear something similar sometimes if I just ran up stairs and started recording too soon - the mic picks up my heartbeat. But this would be a fast rate and it's consistent the whole way through - anyway, it's something that clicks.

I used to have this problem when I was a field audio engineer using lavs especially with people that didn't have much body fat or who were nervous or moving a lot.

Otherwise, sounding great and glad you were inspired by my blog. Has a nice open sound and the noise floor is good.

I have a confession - in the summers I move back into the walk in closet so I can run the AC 24/7 in the Atlanta heat. But if it's cool in the morning I'll record a few sessions in the office.

Good luck!

Edit: Wait, do you wear a watch? Could be that.
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FinMac · Posted: Wed Jun 01, 2016 11:41 pm Post subject: Click

Thanks Lance for the good feedback about the room. That is what I needed to hear Smile

The Click thing is strange. No clocks or watches in the space. Have a wristwatch that is digital and I even remove it before recording.

This noise appears only after the solar panels on the roof start getting hit with sunshine and the inverter downstairs starts making noise.

Could be the mice in the walls clipping their nails but they always wait until the sun is up.

Tomorrow I will post two samples recorded about 10 minutes apart, just Room Tone, with me in the small space recording and nobody in the large space. Hope that will give more insight.

Thanks for your help!
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www.scottsvoiceover.com - An American voice in Finland

"If you want to get to the top, you have to get off your bottom". (Unknown)

Jason Huggins · Posted: Thu Jun 02, 2016 9:33 am Post subject:

The click sounded to me like it was one instance of a mouth click and you just copied a portion of room tone (that wasn't entirely silent) and then pasted it a few times to add some space.

FinMac · Posted: Thu Jun 02, 2016 9:38 am Post subject: Just room tone

Here are 2 recordings of room tone. In both recordings I was in the small room, no where close to the mic. It was just the mic recording the room.

In the first instance, if you check in Adobe Audition frequency analysis, you will see there was not very much noise in the recording, mostly between - 68 to -70 dB. Then the second 5 seconds there is more noise, between - 65 and -68 dB and that spike around 15 - 17 kHz shows up.

The first 5 seconds were recorded before the solar inverter woke up, and the second 5 seconds after the solar inverter woke up.

Is there a clicking sound in the second 5 seconds or what ?

Thanks for your help!!!

https://www.dropbox.com/s/06ujhzxqj2arumj/5%20seconds%20RT%20before%20and%205%20seconds%20RT%20after.wav?dl=0

And Vernon, I will have to search for my dummy-plug !
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www.scottsvoiceover.com - An American voice in Finland

"If you want to get to the top, you have to get off your bottom". (Unknown)

Jason Huggins · Posted: Thu Jun 02, 2016 11:27 am Post subject:

I didn't hear the clicks on this sample. I did also notice that there is some low frequency noise when the inverter kicks in as well. Sounds like it is around 100Hz and below. It is definitely the inverter that is casing the noise. Now it's just a matter of determining HOW it's getting into the audio. Have you tried your stethiscope idea yet? Even a screwdriver pressed up against your ear (NOT THE SHARP SIDE...the blunt handle side) will result in bone transfer of any vibration and you should be able to hear it. Especially long thin screwdrivers.