Trial B-Format recordings

Now that the recorder and microphone are ready to go I decided to test out the setup in some controlled environments. I was lucky enough to be in Inveraray at the end of January visiting the George hotel. At the hotel, on holiday, was a 30 strong student choir from Trondheim in Norway. They performed 4 or 5 pieces of music in the busy public bar. I had obtained permission to record them and here are the results:

Candiss Wont you come home Bill Bailey by seegee

Candiss outro by seegee

The b-format recordings were transferred into Pro Tools in order that they could be edited and mixed. To listen to any b-format recording we must first 'decode' the signals to suit the monitoring configuration. In this case stereo. This can be done in several ways but the most effective, and flexible decoding method is achieved by utilising the (W) & (Y) channels to obtain Middle and Side, or Sum and Difference. The (W) or Omnidirectional channel is used as a reference and is panned to the centre. The (Y) or left/right facing Figure of Eight channel is panned to the left giving us M+S=L. A duplicate is made of the (Y) channel, phase inverted, then panned to the right giving us M-S=R. To vary the apparent width of the recording we simply vary the amount of Middle to Side which in turn causes various amounts of phase addition and cancellation.

Below is a diagram showing how the microphone capsules work together to provide spatial information.



Below are the screen shots of the mix and edit windows showing the waveforms and the mixer settings.






The next stage of the process is to listen to the b-format recordings through a 5.1 monitoring system. This time the files were imported into Logic and a 'plug-in' was inserted across the track which routes the appropriate combination of signals to the appropriate speakers. As we discovered in an earlier post, b-format recordings differ greatly from traditional stereo or multi-channel techniques, because they do not rely on a specific number of speakers to replay what has been recorded. As a result of this there are a few products on the market that enable us to take advantage of b-format recordings coupled with 5.1 speaker set-ups. Two of these products were tested out yielding incredibly satisfactory results.

The product that I shall be using for the generation of 5.1 is the Soundfield surround zone plug-in. As we can see from the image below the plug-in allows us to route b-format signals to a variety of speaker configurations. During the listening tests I noted that it was very difficult to pinpoint the speaker positions which can often be the case when employing other spatial microphone recording techniques....this is exactly what I had hoped. I will discuss this in more detail in a later post.



The 5.1 recordings of the examples above have been included on the DVD that accompanies this blog.

The references for the images used have been detailed in the accompanying documentation.