Transition between recording sessions

Narrating and Producing Audiobooks.

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Re: Transition between recording sessions

Permanent link to this post Posted by kozikowski » Mon Jan 23, 2017 11:51 am

http://www.kozco.com/tech/audacity/Docu ... ch.xml.zip

Unzip it and add it to Equalization.

Adding Audacity Equalization Curves
-- Select something on the timeline.
-- Effect > Equalization > Save/Manage Curves > Import
-- Select LF_rolloff_for_speech.xml > OK. (it won't open the ZIP. You have to decompress it)
-- LF rolloff for speech now appears in the equalization preset curve list.


Use it with the Length slider at about 5000 (mid).

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Re: Transition between recording sessions

Permanent link to this post Posted by solobo » Mon Jan 23, 2017 1:49 pm

After reading your comments and looking again at all the files, I'm starting to think I must have been a tad closer to the mic on track 2. Seems like my overall recording volume was louder in that track.

Peak/RMS/Noise: raw recordings:
Track 1: -6.0dB / -30.3dB / -70.3dB
Track 2: -2.6dB / -26.9dB / -69.8dB
Track 3: -3.9dB / -28.4dB / -67.3dB
Track 4: -4.4dB / -29.2dB / -70.3dB

As far as noise, it seems like LF rolloff helped the margin on that:

Noise: after setRMS & Limiter + -3dB noise reduction (all on a per-track basis):
Track 1: -62.8dB
Track 2: -65.7dB
Track 3: -61.7dB
Track 4: -64.0dB

Noise: after LF Rolloff:
Track 1: -64.3dB
Track 2: -68.3dB
Track 3: -63.4dB
Track 4: -66.3dB

As for the 120Hz hum, I wonder if my monitor could be the cause? My setup: I'm in a closet, my desktop (HP) is outside the closet, but my monitor and Blue Yeti microphone are inside. The microphone is set to cardioid but the monitor behind it is only about 12 inches away (24 inch Samsung monitor). The USB cable for the Blue Yeti is also pretty long, about eight feet; not sure if that makes a difference. I thought of using a notch filter, but it doesn't look like a sharp 120Hz peak, so that probably wouldn't help much?

Attachments: the 1-2 transition before any processing (raw) and after adding the suggested LF Rolloff eq to the previous mastering (SetRMS, Limiter, -3dB noise reduction).

transition1-2-premaster.wav
(760.04 KiB) Downloaded 18 times

transition1-2-postLFRolloff.wav
(780.3 KiB) Downloaded 16 times
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Re: Transition between recording sessions

Permanent link to this post Posted by flynwill » Mon Jan 23, 2017 2:28 pm

Closer to the mic may well explain the difference. You are aware that Yeti is a "side firing" microphone, right? Meaning you want the "Blue" logo to be pointed at you, not the end. If you are off center you will get differences in timbre as well as volume.

It would be a simple experiment to find out if the monitor is the source of the hum: Set audacity running, leave the closet, and the unplug the power cord on the monitor after a few seconds and let the recording keep going. Compare the before and after parts of the recording. I suspect you'll find that source something else. Florescent light fixture, electrical panel on the other side of the wall, etc. With a pair of headphones, and with the volume turned all the way up you can move the microphone about the space much like you would a metal detector to locate the source. If your computer is a laptop, try running it on battery power only.
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Re: Transition between recording sessions

Permanent link to this post Posted by kozikowski » Tue Jan 24, 2017 12:41 am

Like that guy at the beach searching for diamond rings and Rolodex watches.

That's pretty much exactly how I found my humming bass cabinet. I'd had background hum in every shoot for months and I was working by finding the one place in the room with the least hum and doing everything there.

I set up the microphone on a boom and headphones turned up and started trolling for sound. Turned out not only did the bass cabinet produce a low volume hum, it made an electric hum as well, and it did it with the power turned off.

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Re: Transition between recording sessions

Permanent link to this post Posted by solobo » Tue Jan 24, 2017 2:13 pm

you want the "Blue" logo to be pointed at you, not the end

Right, yep, that's the way I have it set up.

I tried the metal-detector technique a little, but couldn't hear the hum. I tried to find it by plotting the spectrum from a few different mic positions, but I'm not seeing any 120Hz spike in any of those either; maybe it's more subtle?

Here's a 15s sound sample:

First 5 seconds: mic with Blue logo side pointed at the monitor about 1" away.
Second 5 seconds: mic in normal recording position (about 12" from monitor, Blue logo pointed towards me)
Third 5 seconds: mic in normal recording position, monitor unplugged.

Do you guys notice a difference in hum? Plotting the spectra, I don't see much difference, though if anything the least 120Hz seems to be in the normal recording position (second 5 seconds)?

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Re: Transition between recording sessions

Permanent link to this post Posted by flynwill » Tue Jan 24, 2017 2:27 pm

Some changes from the defaults that make the Frequency analysis window a bit more useful:

Set the "size" to 8192 or greater. The bigger the number the more detail you will get in the spectral peaks. (But you do have to choose a sample with at least that many points).

Set the Axis to "Log Frequency". Log Frequency spaces the frequencies more the way we hear them. (The notes of a piano will be evenly spaced on this scale).

Ironically the 120Hz noise is about 4db lower in the middle of your three samples, indicating that moving the mic over next to the monitor moved it away from the source. (Or that pointing it towards the monitor pointed it away from the source.)
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Re: Transition between recording sessions

Permanent link to this post Posted by kozikowski » Wed Jan 25, 2017 1:41 am

There's a five dB drop in 120Hz hum between the first five seconds and the second. That's significant. 6dB is half.

If you can't hear this from the headphone connection of the microphone, then running down the cause can be a career move. You have to substitute bookkeeping and memory.

What kind of lights do you have? Turn them all off while you're making a recording and announce it. "Here's the desk lamp....here's the room ceiling lights..." Lights, particularly fluorescent or CFLs are famous for making noise. We did a mini-contest at work as to which ones were the quietest. LEDs don't seem to have a noise problem. Do you have older tungsten lights with dimmers?

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Re: Transition between recording sessions

Permanent link to this post Posted by solobo » Wed Jan 25, 2017 2:14 pm

Some changes from the defaults that make the Frequency analysis window a bit more useful


Ah, got it, now I see the 120Hz spike.

Ironically the 120Hz noise is about 4db lower in the middle of your three samples, indicating that moving the mic over next to the monitor moved it away from the source.


Actually, the middle sample is one in my normal recording position. The only difference between sample 1 and 2 is mic position (monitor is on in both 1 and 2) - indicating that normal mic position is better than close to the monitor. But the only difference between sample 2 and 3 is the monitor state (plugged in in 2, not plugged in in 3) - indicating that unplugging the monitor made things worse... ?

The light is a single tungsten bulb in the closet I'm recording in. There are more tungsten bulbs in the bedroom about 10 feet away behind a closed door.
170124_120Hz_hum_search_1.JPG
170124_120Hz_hum_search_1.JPG (14.03 KiB) Viewed 251 times


I did the experiment Koz mentioned, recording and saying what position I was in. I then went and plotted the spectra for six different positions:
170124_120Hz_hum_search_2.JPG
170124_120Hz_hum_search_2.JPG (47.75 KiB) Viewed 251 times

170124_120Hz_hum_search_3.JPG
170124_120Hz_hum_search_3.JPG (52.41 KiB) Viewed 251 times


First test: mic close to monitor, 120Hz level pretty low --> probably not the monitor
Second test: mic close to the light, 120Hz level 9dB higher --> it's the light!
Third test: mic close to the light, light switched off, 120Hz level the same --> it's not the light?
Fourth test: mic close to the light, light switched off, closet door closed, 120Hz level 5dB lower --> ???
Fifth test: mic close to the closet wall that has the PC on the other side, 120Hz level low --> it's not the PC
Sixth test: open the door, put the mic directly next to the PC, 120Hz level very high --> the PC is loud, but not getting through the wall.

My conclusion from this is mainly that I'm confused. Could it be the light fixture itself, humming even when the light is switched off? Or could it be power to the microphone from the PC (i.e. an electrical hum, not a recorded sound?).
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Re: Transition between recording sessions

Permanent link to this post Posted by kozikowski » Wed Jan 25, 2017 9:27 pm

My conclusion from this is mainly that I'm confused.

This search is not for the easily frightened. You can have two different sources of hum and under magic conditions, they partially cancel.

Does it change depending on whether or not you're touching the microphone? If you have an imperfect connection between the microphone and the computer, or an imperfect connection between the computer and the wall socket, touching the microphone can make a huge difference.

I've lived in two houses and both of them had some wall sockets wired wrong. "I know you're expecting the protective ground connection to be on the round pin (in the US)."

I'm trying to think of a method of live monitoring. There's just nothing like real time symptoms to straighten out a problem. How about Record your microphone in Audacity with the volume controls all the way up. Then turn the computer's volume controls all the way up and listen to the computer. Don't drop the microphone while you're on headphones.

And no. Unless it's broken, there's nothing about an undimmed standard tungsten bulb or socket that makes noise.

In my own case I was whipping out magic theories about getting hum from the neighborhood high-tension wires which go over the house. But I couldn't prove it and none of the tests pointed that way. Maybe a broken wire under the house.....ahhhh.....nope.

Unplug the bass cabinet. BANG! Total silence.

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Re: Transition between recording sessions

Permanent link to this post Posted by kozikowski » Wed Jan 25, 2017 9:32 pm

If you can't hear yourself, you should make sure that Preferences > Recording: [X] Playthrough is ticked.

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