Hi, I just discovered something I didn't know about microphones, and maybe it can be useful to someone else (but I guess the most experienced amongst you can skip this message).

Some days ago I wanted to record both some acoustic instruments and my keyboard. Since my laptop has only a “mic-in” input (no “Line-in”), I used a small mixer board I have, connected a microphone (to capture sound in the room) and the keyboard to the mixer, and the mixer outs to the “Mic-in” input (with proper cable/adapters).

All OK, except for the fact that the microphone signal was very low, even turning the gain and level mixer sliders all the way up.
After some tests and research I understood that the microphone I was using (a “dynamic microphone”) is meant for voice recording, so if you want to record some acoustic instrument you have to keep it very close to the sound source.

This was not very convenient for me so I realised I needed some “ambient microphone” instead, and I recalled that I had one of these, a cheap “computer microphone”, the kind you can put on your desk and use for audio/video conferencing, able to capture sound even if you are not very close to it.

Here is what puzzled me: to my surprise this mic works fairly well if it's connected directly into the Mic-in of the sound card, but if I plug it into the mixer, it almost can't pick any sound, instead it gives a really high buzz, or “hum” noise (BTW, the noise gets even louder if I grab the microphone cable ) I tried tweaking the mixer and soundboard controls, without success, so I tried replacing the adaptor I used to plug the mic into the mixer (3.5mm to 1/4“ jack), but that was not the case.

To cut a long story short: I did some research and I finally found that this kind of microphones (”electret microphones“) are only meant to be used with ”Mic-in“ input of common soundcards, since they need a small amount of current to work, and this is supplied by the ”Mic-in“ socket (someone calls it ”plug-in power“). I guess that's also why they have a ”stereo“ 3.5mm jack (not for L/R channels, but I guess for the power?).

Later a friend explained me that for ambient recordings, one usually needs a ”condenser microphone“, which is quite expensive (compared to dynamic mics) and also needs a power source (”phantom power"), but unfortunately my mixer board can't provide it.

So it seems that the only solution for me is to use my dynamic microphone and get a microphone stand to keep it as close as possible to the sound source, unless someone can suggest other ideas…

Cri
Some days ago I wanted to record both some acoustic instruments and my keyboard. Since my laptop has only a “mic-in” input (no “Line-in”), I used a small mixer board I have, connected a microphone (to capture sound in the room) and the keyboard to the mixer, and the mixer outs to the “Mic-in” input (with proper cable/adapters).

I spent a lot of money for computer microphones and usb sound cards (not expensive but too many) especially for usb microphones (they come with their own sound cards and are eliminating the use of the mic jack of the laptop sound card) of course they doesn't mix with keyboard. For mixing I bought a little guitar amp with a 3.5 mm socket for mic and a 6.3 mm socket for guitar. Of course I was very carefully to find an amp with 3.5 socket for headphone out and in this socket I put the cable in laptop mic socket!!! The sound of the amp it is cut by the cable put in the headphones socket but the laptop speakers play the sound instead. The level of the signal is enough at my amp. The amp was around 25 usd.

An usb mic is very easy to stick on the guitar body in order to capture the sound near the mic but I also tried to register with a transducer pickup build with a clip (around 5 usd).

An usb sound card return the mic, headphone and line jacks to new laptops. Usually mic jack (only) from a new laptop is combo (for headphones too, as for smart phones)