Stereo image with mismatched mics
Great topic.
The important thing about a stereo recording is the stereo image. When you are a comfortable distance from your speakers listening in their sweet area the stereo image lends space and reality to the audio experience. It sounds much more like live music in the room then a mono recording can.
There are many ways to record a stereo image with two or more mics. Two standard ways are X/Y where two cardiod mics are set in front of the music with the mics close together but at an angle, often 110 degrees, and Spaced Pair where two omnis are set in front and to either side of the performers.
If you use omni mics in a close X/Y configuration you usually end up pretty close to mono. Cardiod mics in a spaced pair can result in very uneven coverage of the performance area. Neither of these is recommended.
So if you got cardiods try X/Y. If you got omnis try a spaced pair.
Either of these techniques will get you a wonderful spacious stereo image.
Naturally if you are buying a pair of mics for stereo recording you will want a matched pair. Some mics, like the EV RE15 and the EV RE55 are speced tight enough that any two are supposed to be a matched pair.
But say you don't have a matched pair. Maybe you've got two EV 635a omni mics or two MXL 603 cardiod mics. Use them anyway. You'll still get a great stereo image. Most people most of the time on most hifi systems won't notice the difference.
Using different mics entirely works too. Sometimes. That is sometimes you get a real nice stereo image from mismatched mics and sometimes you don't.
It has happened that I've had an open vocal mic recording during a live performance that ended up being my right channel in a stereo image. Kind of a spaced pair with one omni and one cardiod. Sure this isn't recommended but if it's what you've got and you end up with stereo you don't say I won't use it because I didn't have a matched pair.
That said I want to address an issue I call purity. The example of mismatched mics above would be what I consider to be impure. And the problem with losing purity is that you only know what your audio sounds like on your monitors. It is very likely that in different listening scenarios, car stereos, theaters, boombox, the stereo image wouldn't be as good as it sounded on your monitors. It could be that it doesn't sound as good on a lot better monitors than the ones you used to mix it.
As an example of a pure recording I take two msh-1 omnis on a Jecklin Disc and I record
acoustic guitar and then I take those signals and they become my left channel and my right channel I just balance and do some light post to make it sound great.
With a pure recording whatever system you play it on it's going to sound as good as it can. You will find some crappy systems where it doesn't sound good but you are not going to take it to a really good system and have it sound crappy. For the most part it will sound as good as the system it's being played on.
Stereo purity equals using matched mics set up carefully to capture a stereo image and then being very careful not to step on that image in post. The advantages to stereo purity are simplicity of production and post production and, more importantly, the audio will sound as good as the systems it's played on in most listening environments.
So since we have this great thread going on the theory of stereo I thought I'd add my concept of stereo purity to the mix.
Thanks,
Hairy Larry