Monday, 8 September 2014

The Recording Session

In june Bob Whitney and I recorded the Cameo Quartet for this project. They played really well and Bob was his usual excellent self. He was always one step ahead of a quite fast moving session and we couldn’t have been so productive without his valuable input.

The set up was relatively complex. I spent the evening before searching in the roof of the Stevenson Hall for multiway boxes. The boxes and cables were primarily installed for BBC broadcasts and it seems that one has been faulty and I think may have been taken away by them to get fixed/replaced! This meant I had to bring down the only remaining box in the roof and drop cables for the ambient mics down to the floor which is a little bit of a pain as this limited the number of available channels and we had to make some set up adjustments (discussed later).

The rest of the set up was relatively painless, although an amount of time was lost sorting out the headphones. Unfortunately there was some slight user error on my part. But once we got started the session ran smoothly.
While we were checking levels and tweaking mic positions Bob and I were struck by how easy recording can be when done in a good space. Bob and I were talking about various engineers over lunch and their approaches and I was telling him about Trygg Tryggvason’s book chapter “Classical Music” in Sound Recording Practice Bob read the chapter after the session and the passage he picked out most clearly was:

“The criteria by which a suitable location for a recording is chosen will not be dealt with in detail here. It should be stressed, however, that a good complementary acoustic is the most fundamental requirement for music recording, without which all subsequent operations are necessarily compromised.”

This isn’t a revelation for Bob or I, more a confirmation. We often talk about the importance of the room sound and how fundamentally classical recording is relatively simple, but infinitely subtle. The ideal is always to capture the sound on as few mics as possible. This will reduce phase issues and will keep the sound from muddying. I believe that if engineers spent more time tweaking main arrays than adding spot mics more recordings would sound clear and clean.

Capturing a stereo image comes down to making a number of decisions and answering a number of questions:

  1. What is the final playback media? (headphones, speakers, multi-channel sound system,  electroacoustic diffusion, iPods)
  2. What kind of image is most appropriate for the music?
  3. What kinds of sound sources are present? (Essentially mono – a solo instrument, properly stereo – ensembles, piano, tuned percussion)

So for this recording the playback medias will be stereo speakers and headphones. I wouldn’t expect anyone to want to listen to this on headphones in the street so it doesn’t need overly compressing – if at all.

The image, as discussed earlier, is wide. However, distance is the most important spatial parameter.

A quartet is properly stereo. An individual clarinettist would be a good example of an essentially mono source. Capturing a single player in stereo will create a stronger, richer image, however, the clarinettist will still be positioned in the centre of the stereo field. Individually, therefore, the clarinettists are essentially mono, when combined they create a stereo image.

Stereo sound stages are created in a number of ways. Coincident techniques provide strong lateral imaging whilst spaced techniques capture depth more effectively. For coincident techniques the difference in amplitude (loudness) of the sound at each mic capsule determines its position in the stereo field whilst time arrival differences create a stereo image using spaced microphone techniques. Spaced techniques commonly use omnidirectional microphones which means they capture more of the room sound than coincident techniques that use cardioid microphones.

Adding more mics to these main arrays creates time differences between the different mics (spot mics will receive the sound earlier than main arrays and ambients will receive it last). These micro delays in time arrival can both help establish a sense of depth or create instability in the stereo image. It is the job of the engineer to manage these issues, selecting which recorded perspectives can be combined effectively.

Having said all this, to make a great sounding recording it is really a very simple equation. Whilst carefully selecting a space and recording method the most important aspect is, of course, the actual performance. Perhaps great recordings can be summed up by the following equation:

(Great Mics + Great Posotioning + Great Acoustic) X Great Performance = Great Recording

The space we recorded in is the Stevenson Hall at the Royal Conservatoire of Scotland. Below you can see a picture of the quartet and I, the mics and stage. This should give you some sense of the scale of the room. A medium sized concert hall, good for large chamber ensembles, but it can work well for smaller ensembles (from solo instruments) and can accommodate a symphony orchestra with a sensitive conductor. It is a good size for this piece. Whilst there are only four clarinettists, when the fixed-media part is added the scale of the piece feels relatively large. The vertical space in the hall, in particular, allows the sound to breathe.

Whilst we were setting up we decided to change a few aspects of the system plan. We decided not to use the Decca Tree for a variety of reasons:
  1. We felt the distance between omnis in the Faulkner array and the decca tree was too small to make the wider omnis useful as outriggers.
  2. The tree does not offer the ability to balance the relative proximity of the clarinets in the mix.
  3. Outriggers seemed to be more crucial rather than simply adding another kind of main array.

We ended up with this set up:

Here we have the main Faulkner Array on the wide stereo bar using B&K 4006 microphones (omnidirectionals) and Microtech Gefell M930 microphones (cardioids) These also make up AB and ORTF systems.

In front, the rather larger mic is an AEA R88 mk2. This is a stereo ribbon mic. Ribbon mics are all bidirectional and in stereo ribbon mics they are arranged at 90 degrees to one another. This means you can use them for Blumlein or mid-side techniques. I’ve never been a fan of mid-side, and I’m slightly skeptical about the artificial rendering of the stereo image (you can read about that here Blumlein has its own issues, but as it is a coincident technique offers excellent spatial positioning (for the person positioned in the sweet spot) coupled with a nice rendering of spaciousness afforded by the bidirectional polar pattern.

To these arrays we added spot mics, outriggers and ambient mics.

The Cameos had worked hard in the rehearsal and the more they are playing the piece the better they are engaging with it. In the session we took a full take and then worked through it section by section.

In later posts you’ll hear more examples, but here is a very quick mix of the edit.


TRYGVASSON, Trygg. (1996). Classical Music. In: BORWICK, John Sound Recording Practice. Oxford: Oxford University Press. 210-228.

No comments:

Post a Comment