Electric noise on audio recording

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Electric noise on audio recording

Permanent link to this post Posted by Diubidone » Fri Jun 06, 2008 8:36 am

Ok I'll try to explain my problem the best I can. Please know that I'm not a technician so maybe I'm not using the right words.

I do audio recording with Audacity in my evangelical church in Rome (www.chiesaolgiata.org). We record usually sermons. So basically it's all voice recording. Now...we've had some electricity problems lately but it seems all is ok now.

Recently we had this problem: there was like a "static noise" in our recordings. You could hear it just plugging in the audio jack into the laptop (that jack comes from a mixer). It immediately sounded like ZZZZZZZZZZZZZZZZZzzzzzzzzzzzzzZZZZZZZZ.

After some trys we descovered something I have no idea about: if we unplug the AC from the laptop and use battery only the noise stops and recording goes just perfect. You only hear the voice of the preacher and that's it. Just perfect! As you plug the AC from the laptop back again this buzz starts again.

Some questions:
1. Why does that happen?
2. How can we fix it?

I understand that it's NOT AN AUDACITY problem but a hardware problem. But I have no idea where to ask this. Anyone can help me out or just give me a link to a more appropriate forum?

Regards.
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Re: Electric noise on audio recording

Permanent link to this post Posted by steve » Fri Jun 06, 2008 11:58 am

Diubidone wrote: if we unplug the AC from the laptop and use battery only the noise stops and recording goes just perfect.

This is unfortunately not uncommon. The external power supply may introduce "ripple" onto the supply voltage for every component in your laptop. While this ripple is not enough to prevent the digital electronics in the laptop from working correctly, it can make a complete mess of audio recording and playback.

A new power supply may improve the situation, but I would certainly want to try it out and compare against the old power supply before going to the expense of buying a new power supply.

USB audio interfaces will often improve the situation to some extent, but in my experience they do not fix it completely and some zzzzzzz is still audible, but at a lower level.

The best solution is to charge up the batteries before you start and run from batteries.
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Re: Electric noise on audio recording

Permanent link to this post Posted by kozikowski » Sun Jun 08, 2008 12:48 am

<<<I understand that it's NOT AN AUDACITY problem but a hardware problem.>>>

That's OK. We do hardware.

Your power problems may be more connected than you think. You can get buzz problems like this if the quality of the AC power and the ground system is suffering, or you have two different pieces of sound equipment and the power is slightly different between them.

<<<The external power supply may introduce "ripple" onto the supply voltage for every component in your laptop. >>>

Totally. However, that's not the only failure pathway. One of the two prongs of standard wall power is supposed to be "neutral" or power return. If there is some damage inside the wall or outlet, there can be some power on the neutral connection. This puts a small amount of AC power on all the wires of the power supply and the case of your computer.

[Scene cuts to the microphone] The performance is taking place on a metal desk with the microphone in a metal stand. Chances are, the metal desk really is neutral and might even be connected to ground if it's part of the building.

This means the shield on the microphone cable is grounded at the microphone, but connected to a small amount of AC power at the computer--remember, the whole computer, case and all has a small amount of power on it. In engineering we call this a sneak path--interference coming from somewhere you're not expecting.

You already know what the desperation method is, float the computer. You can also float everything but the computer. That would work, too.

If the computer power supply can be plugged into the wall either direction, flip it over. I have one laptop that will flip, but only works really well one way and not the other.

I know nothing about your AC power, but in the US we can buy a simple tester with three lights, to tell us whether our three-prong wall outlets are wired right.

http://www.acehardware.com/product/index.jsp?productId=3099774

The correct two lights have to come on.

You can try to filter or isolate your equipment from the AC outlet (they make special expensive transformers for that) or you can try and arrange for everything in the sound system to be plugged into the same wall outlet. You can get this problem if half of your sound amplifiers are connected to the north building power and the other half on the south.

Koz
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Re: Electric noise on audio recording

Permanent link to this post Posted by kyrian » Wed Feb 25, 2009 12:34 pm

Found this while looking into similar issues myself, and agree with the comments above.

This appears to be a UK equivalent to the above US/EU tester.

http://www.maplin.co.uk/Module.aspx?Mod ... checkstore

I'm just about to purchase one myself.

You may also find that using an external high-quality pre-amp instead of plugging the microphone directly into the PC (if you're not doing so already) can help mitigate or remove the noise, provided as stated that it's plugged into the same mains supply.
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Re: Electric noise on audio recording

Permanent link to this post Posted by john11smith » Sat Aug 01, 2009 9:43 am

Laptops use "Switched-mode power supply" http://en.wikipedia.org/wiki/Switched-mode_power_supply it's possible that most laptops power supplies work on about 15 kHz frequency. It sounds like zzzzzzzZZZZZZZZzzzzzzzz. Any testers, power outlet filters and so on won't help. The solution is to buy "Linear power supply" or to make a serious modification on your existing power supply (adding extra filters on DC) or
The best solution is to charge up the batteries before you start and run from batteries.
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Re: Electric noise on audio recording

Permanent link to this post Posted by kozikowski » Sun Aug 02, 2009 3:42 am

<<<It sounds like zzzzzzzZZZZZZZZzzzzzzzz. >>>

I don't know that I agree. 15 KHz is the frequency glass TVs use in the US and a vast majority of the TV viewing public can't hear it at all, much less object to it interfering with the show. That and there's a filter inside the computer to help get rid of that, so no. My money is on the problem getting much better or much worse if you flip the power cord over and plug it back in.

Is there provision for the laptop to run from a car? If those cables are available, you can record many hours on an old automotive battery under the table that no longer has enough energy to run a car. Talk to somebody in the church that knows how cars are wired.

Koz
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Re: Electric noise on audio recording

Permanent link to this post Posted by sleahey » Thu Oct 15, 2009 6:55 am

Hi,

My name is Stephen Leahey and I work for a company called Trillium in Australia.

It is my understanding that this problem is caused by an imbalance introduced by the switch mode power supply. Ideally the laptop is intended to be floating, this means it has no connection to ground. It's very common for power supply manufacturers to place a capacitance between the Mains side and ELV (Extra Low Voltage) side of the power adapter to meet Radiated Emissions requirements (EMC). This capacitance is the cause of the imbalance.

When connecting the laptop to peripheral equipment (such as a microphone, or amplifier output) that is grounded the noise is introduced because the floating laptop ground being pulled down to real ground potential causes a voltage to be induced across the capacitor. This in effect causes the whole laptop to bounce up and down at 50/60Hz, and depending on how the power supply is built, can also introduce the switching noise - It is very likely this is what you are hearing in the recording.

The trick to eliminating this is to connect the laptop to only balanced floating interfaces!
We manufacture a product will solve this problem.

Please feel free to have a look.
http://www.trillium.com.au/modules/mast ... sh/?tac=31

Best of Luck!
Steve.
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Re: Electric noise on audio recording

Permanent link to this post Posted by steve » Thu Oct 15, 2009 6:00 pm

I use one of these: http://www.thomann.de/gb/behringer_di20_di_box.htm
As I use a mixing desk, this has the correct connectors for the job whereas the Trillium device has connectors more commonly found on domestic audio equipment.
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Re: Electric noise on audio recording

Permanent link to this post Posted by BobH » Mon Oct 19, 2009 12:53 am

I had the same buzzing problem happening during our recording as well. Read your posts and tried recording again today with my laptop unplugged. Worked like a charm :)

Bob H
Canada
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Re: Electric noise on audio recording

Permanent link to this post Posted by JakSwiat » Sun Feb 03, 2013 12:58 pm

Hi all.

I have similar problem with my Audacity recordings.
I use home PC and this kind of buzz noise is constantly annoying me during recordings.
When I found this forum thread I checked power sockets at my home with borrowed laptop and found out that buzzing sound was appearing only when recording with laptop connected to ungrounded power sockets.
As all sockets in my room are not correctly grounded I ask:
Is there some kind of device or filter that could remove this buzzing noise ?

I know that I can use Audacity noise removal feature but "buzz" is appearing also during Skype calls etc.
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