Sweetening a Live Recording
While I don't make a living as a recording engineer (as many of you do), I still record live classical music fairly frequently, While the musicians are usually superb, the venue often falls a little short. The space may be boxy with a low ceiling. There may be a problematic back wall with a disturbing slap. There may be carpet everywhere except where you need it. Or the space may be perfect except for the whooshing air conditioner or constant stream of traffic. How do you make a recording that's worthy of the performance?
It's obvious that microphones will have to be inside the critical distance, the point at which direct sound is stronger than reflected sound. In smaller spaces that may be only a few feet. Ceiling height plays into this significantly, and a low ceiling may further reduce your choices, driving you to cardioid microphone patterns or tighter. At these distances you'll be running into known issues--putting a mic on a clarinet at one meter is a lot harder than at five. You already know many of the best practices for close-micing: with reasonable skill you'll be able to avoid much of the harshness that comes with being so close.
But where did the reverb go? Eliminating the boxiness and ambient noise mean that you've also lost most of the reverb (this is exactly my intention in some places). You'll need to add some reverb to help the recording, but there are some tricks in doing it. First you'll want to choose a reverb. Generally I'll use PhoenixVerb if I like the balance and don't hear excessive harshness on any of the mics. If the sound is a little sterile, then I might use R2 instead. Sometimes it's a mix of the two--perhaps Phoenix on main mics and R2 on spots. There are no rules other than what your ears tell you.
The Trick In The Tail
It's important to remember that even if the reverb tail on the recording is very quiet, you still have a lot of early reflections in the recording. Why not use them? For my "main" reverb, I find that I generally push predelay out to 40-50 milliseconds and then lower the level of early reflections. It's often helpful to move reverb attack to a higher (later) value. This will help the transition from natural to artificial reverberation. But the "rules" might change for spot mics. For classical recording, the spot mic is used more for focus than for overall level. The spot will often be a little harsh. In this case, a PhoenixVerb with reverb level off, will give you early reflections that you can use to smooth out the spot. Usually a shorter set of reflections (I usually start at 60 milliseconds) with moderate to high diffusion and very short predelay is where I end up. Sometimes I'll bring those reflections directly to the output and sometimes I'll feed them into the main reverb.
One of the great temptations in sweetening a live recording is to make the room much bigger. If the original venue was 50 seats, why not make it into a symphony-sized hall? It usually doesn't work. Musicians play for the room they're in--they actively engage with the space. A small space with short reverb may mean quicker tempi, shorter pauses and other adjustments. You can usually make the room a touch larger, but there's a limit. If you go too large, it will be obvious. Settle for making a better version of the place where they actually played. Reverb level plays into this as well. I find that my reverb is usually mixed in at about -15dBFS or lower.
And finally, one last bit of advice. Never tell anybody you did it. If the players tell you they never heard the room recorded so well, or if they tell you it's their favorite space, just smile and say "thank you". Don't tell them about the traffic or the heating system or the slap from the side wall. Just tell them how much you enjoyed the music.
Here's an example using R2 on a string quartet.