Interfacing Microphones to Computer Sound Cards
Most sound card microphone inputs require a minimum signal level of at least 10 millivolts, but some older 8-bit cards need as much as 100 millivolts. The typical impedance of the PC soundcard microphone input is in order of 1 to 20 kohms (can vary from card to card). The microphone type which works best with computer sound cards is the electret microphone.
Sound Blaster soundcards (SB16, SB32, AWE32, AWE64 or Live) from Creative Labs have a 3.5mm (1/8 inch) pink stereo jack for the microphone input, with the following pinout:
- Signal input (tip)
- +5V bias (ring)
- Ground (sleeve)
Note: Most soundcards will wire the positive DC bias voltage to the ring, but a small number of non-standard soundcards can have the bias voltage wired to the tip. A few cards have a jumper which enables or disables the power to the microphone jack. If the jumper is put on, the bias voltage ( +5V through a few kiloohm resistor) is wired to the tip. Newer mainboards with stereo microphone support will provide the bias voltage for both the tip and ring.
The approximate schematic of a Sound Blaster microphone input circuitry shows that the +5V voltage on the connector is heavily current limited. The card's voltage might not be exactly 5V, but it is usually something between 3 and 5 volts when no microphone is connected.
The electret microphone is the cheapest omnidirectional microphone you can buy. Very sensitive, durable, extremely compact in size, electret mics are used in many applications where a small and inexpensive microphone with reasonably good performance is needed. You can find them in almost every stereo equipment, in consumer video cameras, mobile phones and so on.
The electret is a modified version of the classic capacitor microphone, which exploits changes in capacitance due to mechanical vibrations to produce a small voltage proportional to sound waves. The electret does not need an applied (or phantom) voltage like the condenser microphone - as it has a built-in charge - but a few volts are still required to power the internal Field Effect Transistor (FET) buffer.
The bias is needed for the small built-in FET follower which converts the very high impedance of the electret element (tens of megohms) to an acceptable level (several kohms).
The circuit on the left shows a safe way to connect electret microphone capsules to old, non-standard soundcards. Build this circuit only if the simple schematic below does not work.
A simple modification which works with most soundcards is presented on the right. The circuit works because usually the power is fed to the microphone connector through a few kohm resistor and the DC bias on the tip is removed by the input capacitor inside the card.
How do I record using a microphone?
I'm trying to record some music onto my computer by trying something along the following lines - getting a microphone that I can connect into my computer and using it to record sounds from my un-electric acoustic guitar and some finger tapping/creative drumming. I know it might sound like a stretch but I have a good idea of the sound I want. I've been doing this for some time while just jamming, I just dont know the technical details concerning recording it like what kind of microphone (condenser or stereo I dont really know much about any of that stuff), or what kind of cables or if I need a mixer or what ever the heck an XLR is that my roommate was telling me about, or the software that I would need