- Tom McC., I agree with you completely. In conventional M/S recording, the reverberation balance and the stereo image width are determined in tandem by the M-to-S ratio going into the matrix--there's only one "knob" (whether it's in hardware or software) to turn for both at once. As a result, you don't have the freedom to set each parameter to your liking--you always have to pick a compromise. And the two parameters work in opposite directions, narrowing your range of usable settings to the point where usually, there's hardly any choice, as I mentioned a few messages earlier. For example you can widen the stereo image in playback by increasing the amount of "S" that you're using--but that also decreases the proportion of direct sound in the result, just when you'd probably want to increase it, and vice versa.
The "Double M/S" approach, a three-mike system which was discussed in several threads on this forum a few years back, offers a way out of that bind, as does the four-capsule Ambisonic system. Both are also useful ways of making surround recordings. But they're still coincident miking techniques, and whenever I have a choice I usually prefer stereo miking with some space between the capsules; the localization may not be as precise but the listening experience seems more pleasurable to most people, myself included.
May I interject tangentially?
DSatz has posted here and elsewhere about the relationship between stereo image width and reverberation balance. These are the basic ‘building blocks’ of sound recording in my way of thinking, just one step above the even more basic foundational concepts of frequency balance and level dynamics. When he mentions the challenge of optimizing that balance in location recordings made in unfamiliar surroundings without the ability to monitor very well or at all while making the recording, he sums up what I think makes the type of recording we focus on around here unique compared to other forms of audio recording.
I think one of the best uses of the ability to record more than two channels (other than doing microphone or mic configuration comparisons) is the ability to control stereo image and reverberation balance separately, even if only in a somewhat limited way.
DSatz mentions “Double Mid-Side” and ambisonic techniques as three and four channel recording techniques that offer some welcome ability to “unlink” the typically set relationship between stereo image and reverberation balance and make adjustments to one without compromising the other. I sometimes use ambisonic techniques and the control it offers is heady. But like DSatz, I usually prefer non-coincident mic techniques, simply because I prefer the listening experience I get with some space between the microphones, and getting to the point of my post, I find some of the freedom to adjust things after the recording has been made can be done with non-coincident microphone techniques if one goes a step back and re-thinks some of the basics underlying the configurations.
To get a good understanding of how things work and what is really important in audio recording (or at least what is most important to me), I trend to break things down to basic root concepts and then build upon that instead of simply applying the standard accepted techniques to find out what works best. It helps to be familiar with standard microphone configurations which are more or less “known to usually work”, yet I find it more helpful to try and understand why those techniques work and why the don’t work in various situations, and apply that more basic understanding to the practical problem of how to approach things in ways which increase the potential of getting something that will result in a good recording.
I’ve found understanding those general underlying concepts is key, especially with the type of recording done around here, where there is often no opportunity to monitor while setting up or making the recording, perhaps at best some minimal monitoring via headphones. For amateur live music recording, mic placement and configuration tend to be determined by educated best guess, or “listen and put the mics where is sounds good and relatively balanced”, if we are given have the freedom to do that. Having the ability to adjust the direct/reverberant balance after the recording has been made in even a limited way, without compromising the width/imaging aspects, is very helpful. When I consider which microphone configuration to use for various recording situations, some of the basic aspects I think about are ways to control stereo image width and reverberant balance separately. To my thinking, the big advantage of three and four channel techniques is the ability to dedicate the additional channels to direct/reverberant information, and not just catching a slightly different flavor of left/right information. After all, getting an improved direct/reverberant balance is the primary benefit of making a SBD/AUD matrix. The same underlying concept applies here.
As an example, one specific four-channel recorder technique which has been working well for me has been as follows: Spaced omnis into the first two channels, a directional (cardioid, supercardioid, hypercardioid) mic into the 3rd channel, pointing directly forward to primarily focus on direct sound, and in the 4th channel a cardioid facing rearwards with it’s 180-degree null centered on the direct source. The rearward facing microphone provides control over room reverb and crowd reaction and is chosen and placed specifically to ‘exclude’ as much direct sound as possible, focusing on the reverberant sound of the room and the ambience in it. If I have more than four recording channels, a pair of rear-facing mics works even better (arranged so their least sensitive regions or ‘nulls’ similarly reduce their direct sound pickup), but one gets the job done. A pair also makes for easy, discrete 5 channel surround, which I really dig for “you are there realism”, even though I know most here are not interested in making surround recordings. My reason for mentioning all this here is not to be a cheerleader for surround recording, but to explain how certain techniques give me more control over stereo image verses reverberance ballance in two channel stereo mixes, and how that control helps to make up somewhat for the limited ability to optimize recording setups and monitor them “in the field”.
Hope that helps.
Topic: Mid-Side recording levels (Read 8020 times)