2 mics -> line in?

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pvc

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hi. I know this might be a very simple question but I'm newbies here.

How can I record sound using 2 mics and combine the 2 signal (to make them 2 channels) and feed it into the "line-in" on my soundcard?

currently I'm using sb pro (I know it's a crappy one) and 2 omni directional mics. I need this setting for capturing 2 signals from the same source, so that I can somehow figure out the time delay between the two channel and hence determine the location of the source.
 
I'm not sure what the heck you meant at the end there but...

Recording two microphones with one soundcard is EASY! A little thing known as STEREO is what you'll be utilizing!

What you need is some sort of splitter..a Y adapter would work...that accepts two mono signals and combines them into one stereo signal (one source goes left and one source right...remember, a stereo signal is really TWO *seperate* signals which is why this works).

Then you'll record in stereo and later split the stereo track into two mono tracks with your software.

Basically just make sure that the Y-adapter doesn't COMBINE the signals into a single signal (HIGHLY unlikely you'll find this....that's what a mixer's for....in other words, don't use a mono signal spliting Y-cable).

Go down to Radio Shack (ick!) and look around. If your lucky one of the high school kids on duty will know what you're talking about.

P.S. I appologize in advance if someone here works at Radio Shack. But I think we've all had some awkward experiences with Radio Shack employees. :)

Slackmaster 2000
 
Are you trying to do a physics experiment?

Anyway, what esteemed moderator didn't say is that you wont get much siganl at all if you plug your mics into a line in - you can use the mic input on the soundcard, but the internal amplification will be awful. But maybe that doesn't matter if you're not recording music...? The alternative is to make/buy a pre-amp or simple mixer to amplify the mic signals before they go into the line in of the soundcard.

matt
 
You are correct. I assumed he was using preamps since he didn't mention plugging the mics into the Mic In port as 99% of newbies do.

Anyway, I've used this technique to record from 2 sources and it works well.

Slackmaster 2000
 
thnks for the tips, I think I'll go with preamps. But what kind of gain is typically needed? My soundcard's spec says the mic-in sensitivity is 10-200mV and line-in sensitivity is 0-2V (peak to peak) (don't know if they are relevant to this at all =P)

Oh yes, do I really need to match the input/output impedance? or any preamps will do?
 
I would just buy a little 4-way mixer - this have amplification and pots so that you can vary it. They cost about 25 pounds here (what that is in OzDollars, I've no idea). Having varyable amplification means you don't have to worry about the gain - just twiddle 'til the peaks are the right height. I wouldn't have thought that you need to worry about impedance too much - most audio gear is cmpatible (give or take!).
Like I said, the other alternative (if you're electrically minded) is to make one from a kit from the Oz equivalent of Maplins (electronics superstore), which is significantly cheaper, and lotsa fun if you like soldering and stuff.
Or just use the mic in! Give it a try before splashing out your cash!

Glad to help,

Matt
 
Man, you CAN'T use the mic in with a dynamic microphone. I have seen VERY few commercial soundcards that properly handle the extremely low outputs of a dynamic microphone. And it certainly won't supply phantom power if that's an issue for you.

Line level is fairly standard...or standard enough that you probably don't have to worry about it.

As far as what preamps to use...it depends on what you're doing. Many things can "be" preamps, from Processors/DI boxes like POD's and Sansamp's to active mixers to plain ol' preamps.

What are you looking to record?

I used to record from microphones through my old 4-track which I ran into my soundcard. Now I use an ART Tube Microphone Preamp and/or a Sansamp Bass DI box.

Look around you...there are probably "preamps" abound. When you start looking for something better than what's laying around, look into ART Tube MP's... $110 for a single channel and $240 for a dual channel. I've found these boxes, while marketed as "Microphone Preamps" work well in a wide variety of applications. In fact I often run my bass through the Sansamp and then through the Tube MP to give it more punch.

Slackmaster 2000
 
Hang on, if you can't use the mic input with a dynamic mic, then what can you use it for? I agree the sound quality will be awful, and capacitor mics, as you say, are out of the question, but a sound will be heard. I've used my 10 quid dynamic mic to do audio net-conferencing via the mic in on my SBLive etc. And I think the mic in ports are stereo as req'd.

Matt
 
Yes, I was a bit misleading by saying "dynamic" microphone but I wasn't sure what to call it...."good microphone"... "professional microphone" ??

The Mic Input plug on your soundcard is only good for computer microphones. Perhaps you will get *some* results with *some* microphones* into *some* soundcards, but as a rule of thumb it is NEVER advisable to plug your microphone into the mic input unless you're doing something weird.

I guarantee that plugging, say, an SM57 (or similar "good" or "dynamic" or whatever microphone) into a SB Pro (as this guy has) will not provide adequate results. It will either be inaudible or audible and scratchy/distorted.

When I first started with this stuff the first thing I did was to plug my microphone into my SB16. Since then this topic has been covered in MANY threads on this BBS. In fact I think it's even discussed on the main site....yup:
https://homerecording.com/sound_card_basics.html

Here's a blast from the past ala Dragon:

"The mic jacks on cheapie sound cards are meant only for PC mics (which in case you haven't noticed, have stereo plugs because they use a kind of phantom power from the sound card!). They suck.

It's true, the only thing to plug into (unless you have one of the cool beans new AARK Directs with a real live mic input) is the line in, and that means really that you need some kind of preamp/mixer"

Thread: https://homerecording.com/ubb/Forum3/HTML/000046.html

Slackmaster 2000
 
I'm actually recording 'every' sound from the environment. Actually, my project is about locating a sound source. So I'll have to use at least 2 microphones to locate the sound (using time delay or intensity difference etc). Will line-in do the job?
 
Oh, that changes things. If your project doesn't require great fidelity then you might just get away with computer microphones into the microphone in port on your soundcard.

Although I'm not sure if you can plug two computer microphones into one microphone input jack on your soundcard. The mic in plug is stereo, but it's actually a mono source. According to the tidbit above, the soundcard supplies some amount of phantom power to computer microphones. I am unaware of the actual workings of computer microphones since they're not typically used for the stuff most of us around here do.

Do you know what kind of microphones you'll be using yet? If you can get them to line level (via some sort of preamp) then you're set. As recommended above, small active mixers can be had pretty cheaply. Visit radio shack. (yuck!)

Then to record both sources at the same time simply follow the instructions above (minus the microphone input).

You'll also need some software. Look for Goldwave (www.goldwave.com) ... it's pretty nice. Since you'll be recording a single stereo track and splitting it, any wave recorder with basic editing functions should work for ya.

Slackmaster 2000
 
thnks for the tips.

I tried to put 2 mono mic and combine them into a stereo plug then plug it in into mic-in but it doesn't seem to work at all. From then on I had assumed that mic-in is mono. That's why I wanna use line-in. It's probably better if I describe about my project in a bit more detail.

The project is about recognizing and locating a sound source by a robot. The sound source can be *anything* but to make the robot recognizes any sorts of sound is a bit too hard. So the robot might be made to specialize in recognizing human speech, ie to respond to a particular person whenever that person is speaking. So quality of sound is probably important here. I've tried to record sound directly from mic-in but it sounds yucky and very noisy. What do you guys think? I'm really newbies in sound and hardware so those are just my assumptions. Oh yes, I'm running linux on the robot.

The mics I'm using may probably the usual omni-directional electret. Currently each of them is connected to a preamps before combined into a single stereo plug. would that work?
 
Yep, that'll work just fine. Sounds like a very cool project.

Just make sure that your Y-adapter isn't a splitter. That is, you don't want to use an adapter that splits a stereo signal into two stereo signals....you'd have to use it backwards I guess, and it wouldn't work well.

You need a Y-adapter that combines two mono signals into one stereo.

Then you connect the output of one preamp into the left mono plug of the Y-adapter, and the output of the other preamp to the right plug. Then plug the stereo side of the Y-adapter into the soundcard.

If you're using a mixer of some sort, then you'll pan one microphone hard right and the other hard left, thereby seperating the signals (unless the mixer sucks). Then take the line out of the mixer into the Y-adapter. This will sort of depend on your mixer's line out. Typically they will be RCA plugs so this will work fine with a straight through RCA patch cable (unless the Y-adapter is long enought to plug directly into the mixer) If the line out is a 1/4" plug, you don't need a Y-adapter, just run a line straight to the line in on your soundcard.

BTW, one more little thing you might need, depending on what you get, is a 1/4" to 1/8" adapter since your soundcard's line in plug will be 1/8" and many audio cables have 1/4" plugs. If you get one, make sure it's a stereo adapter. I know it sounds stupid, but you'd be suprised at how often people accidentally insert mono adapters into stereo signals. :) (myself included)

Slackmaster 2000
 
thks alot. It worked! I can now get sound in and process it. But another problem cropped up: The mics I used are to insensitive for recording sound that is a bit far away. I used 2 ordinary uni-directional electret, didn't work. When a person is talking say 2-3 meter away, very vague, if any, sound was recorded. Using 2 ordinary omni-directional electret gave similar results.

We are aiming at using not-to-expensive mics for this project to insist generality and portability. Any suggestion on the type of mics we can use?
 
Well, if you're sure that you can't just crank the gain up a little bit...

You're probably going to need a more expensive condenser/electret microphone. I've heard from people on this board that the Rode NT1 is an extrememly sensitive microphone and runs under $200.

Slackmaster 2000
 
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