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  #16  
Old 09-25-2020, 09:25 PM
Chipotle Chipotle is offline
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I don't know if you talked about your room size or treatment anywhere. Any chance it could be room resonance at those frequencies? Room EQ Wizard might give you a clue.
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  #17  
Old 09-25-2020, 10:08 PM
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Originally Posted by ChuckS View Post
The worst noise for me is a pretty narrow band around 50Hz to 60Hz, not quite as bad around 30Hz, and lower but present at 120Hz and 180Hz. So, it sure seems related to equipment/appliances running off of line power. The 60Hz level is at -60dB down from full scale. When I have my HFP set to 50Hz the level at 50-60Hz drops to around -63dB. I can set my HPF a bit higher (mayber 75Hz) and get improvement for the 30Hz and 60Hz noise, but it obviously doesn't help at higher frequencies. (The test was done fairly early in the morning; no road noise. House closed up. No HVAC on. No fans on. Fridge could be the source.)
When I was tracking down noise, trying to improve my studio setup, I spent a lot of time throwing breakers. It's amazing how quiet a "silent" house can get when you turn off all the power. Hard to do if others are home tho, unless they're willing to help with the experiment.

You could potentially have noise from power sources as well, a power conditioner could help in that case, but it doesn't seem like the most likely candidate.

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Using the mics and gain and HPF that results in -63dB noise floor at 60Hz, my recorded signal are generally in the range of -20dB with peaks around -10dB. So, the S/N isn't great at the low end of the spectrum, but maybe not atypical of home rooms. The problem seems to be that there is quite a level of mud below 200Hz, of particular concern as the s/n is not very good if I'm playing low notes not too loudly.
Mud in the low mids may be a different issue, that's one of the things room acoustics is all about, and the lower frequencies are where the biggest issues usually are. Basically, your room has resonances, just like your guitar. When I first started recording acoustic, in an untreated room, my low G always sounded weird, boomy. As I learned more about it, I was able to calculate that I had a big resonance in that room, right at that frequency. Nothing you can do other than acoustic treatment, or a different recording space that has different resonances.
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  #18  
Old 09-25-2020, 10:16 PM
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Regarding looking at a meter for power line noise (that 50-60 Hz) have all the audio equipment plugged into the
same outlet, not two separate outlets a few feet apart or so. Have mikes plugged into the inputs you are listening
to so as to not have open loop noise.
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Last edited by rick-slo; 09-26-2020 at 12:02 AM.
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  #19  
Old 09-25-2020, 10:20 PM
phcorrigan phcorrigan is offline
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Quote:
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The worst noise for me is a pretty narrow band around 50Hz to 60Hz...
Are you sure you're not getting noise from a ground loop?
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  #20  
Old 09-26-2020, 07:53 AM
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I shot these real time analyses of my living room for you last night and this morning on a quick and dirty RTA I have on my iPhone. Last night I left the ceiling fan on but it is a nice Hunter hung nine feet up, halfway between floor and ceiling. I hung and balanced it myself and from my location the slow speed it was set to is below the threshold of hearing. This morning I turned off the fan and shot the RTA again. The times are at the top of each, with last night's on the left. Pardon the slight scale offset due to me fooling with the zoom.



The conditions: my house is on a boulevard in a suburb and is located about a half mile from a major interstate highway. I waited until there wasn't a car passing and the heat pump had cycled off. The app says it is self-calibrating to your particular iPhone model's mic response but not to the specific mic. I noticed that whenever I attempted to pause the screen for a screen shot by pressing the on-screen icon the low-end tilted up and the overall noise level showed about 3-4db higher, presumably from handling noise. My guitar callus made it hard to activate the pause!

The dogs and I held our collective breaths. Sort of. The 5db of reduced noise from turning off the fan, mostly showing in the low end, can be fixed with a mic's roll off. I could hear power equipment in the next neighborhood and the flow noise from the interstate highway that are reflected in the low end of the graph. What strikes me is how similar the noise is between night and morning.

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  #21  
Old 09-26-2020, 08:39 AM
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Hey Bob,
Thanks for the RTA captures. It’s nice to have a real comparison. My room noise is similar (I did not use a RTA to get SPL, but I calculated it to be 43dB SPL at 60Hz). If I set my HPF at 75Hz I can bring it down to about 37dB SPL.
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  #22  
Old 09-26-2020, 08:43 AM
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Quote:
Originally Posted by Doug Young View Post
When I was tracking down noise, trying to improve my studio setup, I spent a lot of time throwing breakers. It's amazing how quiet a "silent" house can get when you turn off all the power. Hard to do if others are home tho, unless they're willing to help with the experiment.

You could potentially have noise from power sources as well, a power conditioner could help in that case, but it doesn't seem like the most likely candidate.



Mud in the low mids may be a different issue, that's one of the things room acoustics is all about, and the lower frequencies are where the biggest issues usually are. Basically, your room has resonances, just like your guitar. When I first started recording acoustic, in an untreated room, my low G always sounded weird, boomy. As I learned more about it, I was able to calculate that I had a big resonance in that room, right at that frequency. Nothing you can do other than acoustic treatment, or a different recording space that has different resonances.
How much of a deal is room resonance for ‘room noise’ measurement (when nothing is purposely stimulating it like a guitar)? I assumed the room noise and the room treatment were separate issues.
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  #23  
Old 09-26-2020, 08:50 AM
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In my current (literally bedroom and no treatment ) set up, ambient noise has become more of a factor, especially since I had to go to a fan driven metal capable,Graphics card in my older Mac Pro to be able to upgrade to Mojave.
And it is definitely visible on the meters in my DAW.

Here is a real world example. A music video I shot last winter , obviously it is not an acoustic guitar solo so perhaps not near as critical ? BTW the first sound on the video is actually my acoustic still resonating a bit , I did not mute it or wait long enough before starting the video and my count in (typical rookie)

In this Video the mic/s are about 6-7 ft. from the computer. I have a GIK 2' by 4' by 5 1/2" thick bass trap, standing in front of my Mac Pro so it sits in the direct line of sight from computer to mics which helps some . I am relatively new to playing and recording electric lead, so it is what it is

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Last edited by KevWind; 09-26-2020 at 08:57 AM.
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  #24  
Old 09-26-2020, 12:00 PM
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I agree. I even installed a switch in my self-built PC to turn off the low noise case fans when I record. This brought my noise floor down even lower. I am also lucky to live in a quiet area with no traffic noise. Finally, I make sure to position my cardioid mics so the PC is off axis.

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This is one advantage of building your own PC--you can select components that will minimize noise. Those include SSDs, a low-noise power supply, a high-performance, low-noise CPU cooler, large, low-noise case fans, and a case with good ventilation. Even without SSDs, my recording PC is effectively nearly silent, and cannot be picked up by my LDC mics six feet away.
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  #25  
Old 09-26-2020, 01:01 PM
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Quote:
Originally Posted by ChuckS View Post
How much of a deal is room resonance for ‘room noise’ measurement (when nothing is purposely stimulating it like a guitar)? I assumed the room noise and the room treatment were separate issues.
Separate issues. Maybe I misunderstood, but I thought you were saying you heard mud in the low end of your recordings, and related to playing notes louder? If your recordings sound unbalanced, that could be room acoustics. If you mean you hear muddy noise when just listening to "silence", then that's some sound being picked up by the mics.
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  #26  
Old 09-26-2020, 01:31 PM
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Quote:
Originally Posted by ChuckS View Post
How much of a deal is room resonance for ‘room noise’ measurement (when nothing is purposely stimulating it like a guitar)? I assumed the room noise and the room treatment were separate issues.
When room resonance is lowered via treatment the room noise will decrease.
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  #27  
Old 09-26-2020, 02:35 PM
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Thanks for all the information everyone!
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