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Topic: Microphones for Computers (Read 5138 times) previous topic - next topic
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Microphones for Computers

I'm seeking information to select a microphone for use with a computer. Certainly others are too.

What I've found out so far is that the common power requirement on midrange to high end mics is not computer compatible:
https://secure.wikimedia.org/wikipedia/en/w...ring_techniques
They use XLR connectors. Are there cables where one end is XLR and the other end a (phone) jack plug?

What Internet resources are available to learn about matching a mic to requirements?
This might develop into a good topic for the H-AudioKnowledgeBase.

Microphones for Computers

Reply #1 –
I think what you really want is a microphone preamplifier. I would not connect a high quality microphone directly to the microphone input of a sound card, at least not an on-board sound card.

Microphones for Computers

Reply #2 –
I agree.  Another option is a mixer.  Most mixers (with mic inputs) can also provide phantom power.  Mixers are more common in 'home studios" than stand-alone preamps, and there isn't that much cost difference between an entry-level preamp and a small entry-level mixer. 


--------------------------
There are 3 common types of microphones:
- Dynamic 
- Condenser (needs power)
- Ribbon (not as common as the other two)

There are two connection/wiring schemes:
- Low impedance balanced (usually XLR)
- High impedance unbalanced (1/4" phone plug for PA use, 1/8" phone plug for computer.)

Condenser mics can be powered by
- A battery
- Phantom power supplied over the audio cable
--------------------------

A computer's mic preamp is high-impedance unbalanced (single wire + ground).  And, most computers have low quality (perhaps noisy) microphone preamps.   

The computer's line input is usually much better.  (A more high-end system will use an an external preamp/ADC box that connects via USB or Firewire, and that keeps the analog completely out of your computer.)   


All professional microphones (stage or studio) are low-impedance balanced (2 wires + ground). 

Dynamic mics (like the very popular Shure SM57 & SM58) don't need power.

Condenser mics need power from a battery or phantom power from the preamp or mixer.

Most "studio" mics are condenser designs, and they usually require phantom power. 

Most performance/stage condenser mics have an internal battery and don't require phantom power.  Some can optionally use phantom power from the mixer.

A ribbon mic is sort-of a specialty item, and you probably won't have one unless you already have several other mics.  In general a ribbon mic doesn't need power.  But since ribbons have low output, some have built-in preamps (like a pre-preamp) and these do need phantom power.

Quote
Are there cables where one end is XLR and the other end a (phone) jack plug?
  Well...  You can get a cable (or an adapter) like that and it might "function", but it's not a proper connection and you won't get the best possible audio quality.  A low-to-high impedance transformer is the proper way to make the connection.  But, you'll still be stuck with your computer's (possibly low-quality) preamp.  You'd also need a 1/4" to 1/8" adapter, because every one of these I've seen has a 1/4" phone plug.    If you've got a mic that doesn't need phantom power, it might be worthwhile to try a transformer since it's a low-cost solution.





Microphones for Computers

Reply #3 –
Quote from: DVDdoug on
A computer's mic preamp is high-impedance unbalanced (single wire + ground).  And, most computers have low quality (perhaps noisy) microphone preamps.   
The computer's line input is usually much better.

So, it is better to plug the mic into "line input" than "mic input"?

Quote from: DVDdoug on
All professional microphones (stage or studio) are low-impedance balanced (2 wires + ground). 
Condenser mics need power from a battery or phantom power from the preamp or mixer.

What does balanced and unbalanced mean in this case?
Quote from: DVDdoug on
Most performance/stage condenser mics have an internal battery and don't require phantom power.  Some can optionally use phantom power from the mixer.

What happens if you connect them to a computer which provides 3V to 5V from the card?

I know the meaning of impedance as far as DC with V=IR and steady state AC with a constant alternating current, but what is the meaning and significance as far as mics are concerned.  The nominal impedance is at 1KHz as I recall.  How can one use the impedance to predict how well a mic matches to the system it connects to?

Microphones for Computers

Reply #4 –
The line input is not sensitive enough for the output of a typical microphone. The added gain on the microphone input is what makes it lower quality (more noise and distortion).

In this case, balanced means that there are two signal wires inside a shield, and the two signals are the inverse of each other. The difference between them is the actual signal. Unbalanced means there is a single signal wire inside a shield and the signal is the difference between the signal wire and the shield. Balanced has better rejection of interference than unbalanced.

Edit: typo

Microphones for Computers

Reply #5 –
A couple of other solutions...

You could get a USB microphone or a USB adapter .

A couple of considerations with these things....  Recording in stereo can be tricky with either of these unless you get a stereo USB mic, and you can't use a USB mic with a mixer.

I'll repeat, "All professional microphones are low impedance balanced".  Anything "midrange to high-end" will be low impedance.  Almost anything you see on stage, in a broadcast, or in a home studio is low impedance.  Almost all of the microphones & mixers sold by   Musician's Friend, or any other music store, are low impedance.  Don't worry about it! Unless you're buying super-cheap equipment, you'll be using low impedance microphones!

Quote
I know the meaning of impedance as far as DC with V=IR and steady state AC with a constant alternating current, but what is the meaning and significance as far as mics are concerned. The nominal impedance is at 1KHz as I recall.
The actual impedance isn't that important....The really important things are the gain/levels and the balanced/unbalanced connection.  But, for some reason (tradition?) we catagorize mics as "high-Z" or "low-Z".

A low-Z (dynamic) mic has an impedance in the ballpark of 200-600 ohms.  I think high-Z mics are in the range of 5k - 10k ohms.  The preamp will usually have higher impedance than the mic.


A high-impedance unbalanced (dynamic) mic (usually) has an internal transformer. It puts-out the same power as a low impedance mic, but a higher voltage (and less current). 

A mic with electronics (i.e. a condenser), can have very low internal impedance and it still might be categorized as a high-impedance mic if it has an unbalanced connection and is level-matched for high-impedance inputs. 

Quote
How can one use the impedance to predict how well a mic matches to the system it connects to?
If you don't have the specs, you can usually tell from the connector.  If you see an XLR connector on a mic, preamp, or mixer, it's usually low impedance balanced.  Phone plugs are usually high impedance unbalanced.  Although, some mixers/preamps have TRS (3-connector) phone jacks for balanced connections.

Quote
What happens if you connect them to a computer which provides 3V to 5V from the card?
It might work, and it might not.    Mics that run from a battery or 48V have an internal voltage regulator (or voltage reducer/divider).  You can't predict what this unknown circuit will do if you feed it 3 or 5V.    (Condenser mics that are made for computers do work from this voltage, but these are usually low quality "communications" mics.)

It's a lot easier just to use the battery.  And, you still have to deal with the wrong impedance/level and connecting a balanced mic to an unbalanced input.  If you're talking about "midrange to high-end" microphones, there is no reason to fool around with Micky Mouse solutions!

Microphones for Computers

Reply #6 –
I've assembled a report based on information, mostly from this forum. Maybe it is something for the knowledge base?  Where can I place it for review?

Microphones for Computers

Reply #8 –
One of the more cost effective ways to connect a professional microphone to a computer is with the use of an external audio interface such as the M-Audio Fast Track or Fast Track Pro. The Fast Track Pro will supply phantom power so is compatible with condenser microphones.
Dan
 

Microphones for Computers

Reply #9 –
A pity that the included software only runs on MS Windows and Macintosh OS.