Reducing Air Noise From Mic

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eatingbananas
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Hi, I'm new here, so forgive me if I'm asking a dumb question. I recently installed Ardour on my laptop (Ubuntu 11.10) and figured out how to record using a mic. Thing is... there's a bit of air noise or "tape hiss" in the recording. Is there something I can do to make it record cleaner? Or do I have to play with the EQ to get that out?

(and yes, the room is totally quiet and the laptop isn't making the noise.)

LeatusPenguin
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First of all, what mic are you using and what interface?

eatingbananas
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I'm plugging a Radio Shack model 33-3043, straight into my laptop via the mic port. It's a decent mic, with a nice thick wire. It does a lot better than the mic I tried first (a mic/headphone combo that was made to use with Skype)

LeatusPenguin
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You're getting that noise cause you're using the onboard sound card. You need a proper audio interface (that's compatible with linux) to hook up the mic with. Plugging it directly into the onboard sound card will give you poor results as they aren't intended for plugging your type of mic directly into. If you search the forums here you'll find what audio interfaces people have found work well with Linux. If you have a proper interface you won't have any hiss in the background as it'll be suitable for mics such as the one you have. Mic inputs on computers aren't intended for the type of use that Ardour is intended for.

linuxdsp
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I'm plugging a Radio Shack model 33-3043, straight into my laptop via the mic port.

The Mic port on any built in soundcard / interface will always give you bad signal to noise (if you must use the onboard audio, and on some recent machines, contrary to popular opinion, it can be possible to get 'acceptable' recordings however, use the line input with an external Mic pre-amplifier.)
To get good signal to noise ratio it is important to get the "gain structure" of the signal path correct, which in simple terms means not adding any more gain than is necessary, consistent with available headroom / dynamic range, at each stage in the signal path.
e.g. you would want most of the signal gain to be happening in the low-noise external Mic preamplifier, but not so much that its output overloads the line in on your sound card, and you would want enough gain on the line in to make best use of the ADC range, but not so much that the ADC gets overloaded by strong signals.
You can use an EQ to reduce noise, but as is always the case, you would do better to capture the best recording initially. High quality capacitor microphones are now available for comparatively little money e.g. Rode NT-1A , and even the Mic input on a small mixer will be better than the one on a soundcard.

seablade
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Also it wouldn't surprise me if that mic you are using is particularly inefficient as well, only exasperating the problem others have mentioned. Radio Shack has not been known for good quality for a LONG time. At the very least it wouldn't surprise me if it is designed to work with a high impedance circuit, instead of the low impedance circuits that professions mics are designed to deliver into.

Seablade

kelleydv
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@eatingbananas: Even if your gear isn't up to par, you can still play with the noise. Start by using a filter. Set the Q parameter high, and boost the gain. When you move the frequency parameter around you'll be boosting different frequencies and hearing more of what's going on in particular frequency ranges. There's probably a narrow range where the "air noise" you're talking about is coming from. There could be more than one "hot spot" where you're getting some kind of unwanted noise. Once you zero in on a frequency you don't like, reduce the gain and hear the difference.

That's probably the most basic approach, but there are others.

bassbass
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Hi

FIRST OF ALL the link should be balanced.

I mean you should have a transformer on the computer side to convert the balanced link into the unbalanced input.

I assume radio shack sales balanced microphones.

You can use for instance the NTE series of transformers from Neutrik.

On "correct" sound cards the balanced input is in the design, you wouldn't have to do anything.

Assume you are not recording the kick drum of a drum set, the transformer should not cut too much on low frequencies.

Cheers

linuxdsp
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@bassbass: balanced / unbalanced lines are completely irrelevant for this problem.

eatingbananas
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Wow, thanks for all the input on this. I didn't expect such a good response. I think I'm going to look into getting a better mic, and a preamp or mixer.

In the meantime I'm going to try Kellydv's idea for reducing the noise as much as possible. Once I get better gear, I cen re-record the vocal & acoustic guitar parts.

Thanks very much to everybody who's replied :-)

I'm a bit new to this. Last time I recorded anything was about 12 years ago... on tapes. Even then, I didn't have to think much about the equipment or engineering, 'cause my brothers did all that for me.

eatingbananas
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On 2nd thought, maybe it isn't the mic? I just discovered that even with the mic turned off, there's an air noise created when I record. I uploaded a 5 second sample of this to http://april29th.be/test.wav ...could it be something else? Or is the mic somehow causing it even though it's off?

joegiampaoli
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That sounds similar to a 60Hz cycle hum, let's call it EMI noise or just interference for simplicity. If you get this noise not only from the mic, then is your equipment/House/Studio properly grounded? Cheap cables? Maybe even the computer, probably even the CPU, check your BIOS and enable spread spectrum (I would leave this one as the last resort), if already enabled then just leave it the way it is.

EDIT: It sounds more like floor noise actually, maybe you are recording too hot? Or input gain too high? There will always be an amount of noise (called floor noise) in the tracks which becomes noticeable either by recording from inputs too high or by recording too low and then turning the track volume up or normalizing to 0dbfs, it would help if you post the same kind of sample but with additional sound like a guitar, mic and see what levels you are recording at.

linuxdsp
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I can't download the file to listen to it (access forbidden) however, it seems to me that the main problem is simply that you are trying to record using the onboard mic input.

1. The onboard Mic input is in the worst environment for a highly sensitive input (e.g. lots of noise from other digital components on the mainboard / power supply noise etc) normally this manifests as hiss, or clicks, chirps or similar

2. If you are getting 50 / 60Hz buzz (or related harmonics) this is most likely due to AC mains 'hum' coupling into the input.

3. Others have suggested balanced lines etc, however, while this will help to cancel the effects of external 50 / 60Hz induced noise on the cables, it will do almost nothing to reduce digital noise picked up in the onboard Mic input circuitry and if you use transformers to do the balancing / unbalancing, this will most likely cause you more trouble than the original problem, unless you are very experienced at designing such systems.

The best way to deal with the problem, is first to get a good quality e.g. capacitor microphone (quite often these have some kind of active electronics in them which helps to correctly buffer the output to drive the Mic cable), then get a good quality external mic preamplifier (or a small mixer with a good quality Mic input). The Mixer / Mic pre will be correctly designed to boost the signals from the microphone without introducing too much of its own noise.
The higher 'line' level output from the Mixer / Mic pre can then be used to feed either an external soundcard, or possibly the line in on your onboard audio. This means you are not using high gain circuitry inside the computer, which means there is less of a problem with digital noise from the other components.

Also, if as you say, you hear 50 / 60Hz hum when you have the Mic 'switched off' it is likely (especially on cheaper dynamic mics) that this is just disconnecting the Mic element from the cable, which then effectively means there is just a long unterminated length of wire connected to the soundcard mic input (don't be surprised if this acts as a very good aerial for AC supply noise)

seablade
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For those that can't listen to the file, this isn't a 50/60Hz hum. It is a noise floor issue, and you should follow linuxdsp's advice in this case. The only real way to help this is to use better quality equipment, as I said Radio Shack is not known for good quality anymore. It is more known for ripping people off by overcharging for poor quality equipment that they sell to those that don't know better as good quality, oh yea and for selling you a cell phone. They will do that.

And yes most of this noise does likely come from having a poor quality (onboard) mic preamp gain turned up to much. This can be helped with a decent condenser mic with phantom power which will output a higher signal level so you don't have to turn up your gain as much, and a better quality preamp. Since your onboard preamp can't put out phantom power for a decent condenser, it means you will need to replace both at the same time most likely, much like linuxdsp suggests.

Using EQ to try to help with noise is a losing battle. While you can do some with it, it will also affect the sound of your recording, most of the time in a big way. It should be used as a last option(Which in your case may be the only option at the moment).

Seablade

bassbass
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One other problem of the built in input on computers is the gain is sometimes automatic. Then when people shut up, the gain raises and then we can listen a lot of noise... perhaps you should build an attenuator to raise the S/N!!!!!!!!!!!!

@linuxdsp I wrote "first of all"

the balanced lines has been invented to fix that kinds of problems. Indeed the common mode rejection reduces the 50 hertz but also some high frequency signal collected by the wires. The side effects of bad input electronics is to work as a radio receiver... receiving everything at the same time.

Also the load impedance should always be close as possible to the source impedance (which I am afraid is not the case for built in inputs). Then if the output impedance of the microphone is 1K and the input one of the computer is 10K, a resistor around 1.11K should be placed in parallel (e.g. in the plug). Professional equipments load properly their inputs.

anahata
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Your radio shack mic is a dynamic. They have lower output than condenser mics, and computer built-in mic inputs are really geared to electret mics (which are a type of condenser mic) which have higher output.

So you do need a proper mic preamp, or perhaps a usb audio interface with mic inputs, and you may then find your RS mic isn't too bad at all.

If you get a mic preamp with phantom power, you could also get a proper condenser mic and most likely get better results. My favourite cheap condenser mic, especially for instruments, is the Behringer C2 - you get a pair of mics plus stereo bar and good quality case, for a ridiculously low price.

Any mic input with nothing plugged in will be noisy if you turn up the gain enough. Don't worry about that too much.

seablade
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the balanced lines has been invented to fix that kinds of problems. Indeed the common mode rejection reduces the 50 hertz but also some high frequency signal collected by the wires. The side effects of bad input electronics is to work as a radio receiver... receiving everything at the same time.

Balanced Input will do nothing to help with interference picked up after the differential amplifier in the circuit that the line connects to. And this is the primary source of interference when dealing with built in sound cards. By itself by the way a balanced line won't prevent a ground loop from forming for example, which is the most common way of non-external 50/60Hz being injected in my experience. Only isolating the ground will do that, which is decidedly easier with a balanced circuit than an unbalanced of course, but it still requires more than just running balanced signal end to end.

Also the load impedance should always be close as possible to the source impedance (which I am afraid is not the case for built in inputs). Then if the output impedance of the microphone is 1K and the input one of the computer is 10K, a resistor around 1.11K should be placed in parallel (e.g. in the plug). Professional equipments load properly their inputs.

Sorry but you are not correct here. The common practice for professional microphones is to deliver into about/approaching 10x their source load. So if we assume typical microphone source impedance of 150-300Ohm for a low impedance professional microphone, they are designed to deliver into inputs with an impedance of 1.5k-3k (Example... http://www.akg.com/site/products/powerslave,id,781,pid,781,nodeid,2,_language,EN,view,specs.html ). This is why the input impedance of most microphone preamps generally are around 2kOhm. (Example http://www.rme-audio.de/en_products_fireface_ucx.php#12 )

Also see... http://www.greatriverelectronics.com/faqs.cfm

And any number of other references I have laying around. I pulled out the sound reinforcement handbook as I am fairly sure it is in there along with a complete breakdown of the math behind it, but I couldn't find it in the brief look I took.

Seablade

seablade
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Any mic input with nothing plugged in will be noisy if you turn up the gain enough. Don't worry about that too much.

While true, the quality of preamp will make a difference in how much internal noise is injected during the amplification process, so some preamps will be able to add more gain with less noise injected into the signal by the preamp itself(Not to be confused with noise already in the signal from before the preamp).

Seablade

bassbass
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Hi

@seablade: This discussion is about how to get the best performances while using equipments that never set record of quality.

The power adaptation (maximum power drawn by the load) is the one that eject the most the parasitic. Your internet site says clearly that up to the 60's that had been being the case. But that's true there are some drawbacks
* Drawing the maximum power is a way to slightly change the sound as your site states.
* Drawing more current than a "half" voltage adaptation (Rin=10.Rout) may cause saturation, thermal distortion etc... On this point I am not agree when they say that switching the input impedance does not change anything is the microphone is buffered.
In all case we have to applied what is requested by the providers
* On stereo or more lines, a special care should be applied on the precision of the impedance. Indeed mismatches on the impedance can cause differences of gain.

The video and the telephone keeps the power adaptation due to the high frequencies or the high length of the wires. You can see what happened on impedance mismatches in the book isbn 2225306133 page 89.

My point of view in this kind of situation is to present the lowest impedance as possible. Loading is a way, an attenuator is sometimes also the way. Parallel resistors in the plug (computer side) can reduce the noise.