Today we did a series of tests with the use of stereo and mono microphones: The test was to see the difference in stereo sound from both microphones and microphone placement. We would hope to see a difference in frequencies, reflections and the field of response. This is how the test went.
AB Mics – cardiod mic’s that were placed 3ft – 10 ft apart
X Y Mic’s (coincident pair) – cardiod 90 to 120 degree pick up mic’s
Binaural (Dummy head recording) – cardiod / hyper cardiod
The AB microphones were placed on the outside of the layout whiles the XY occupied the centre and the Binaural being placed between the two. This was done because the AB would pick us a precise 3D layout of the room which is why they were placed further apart; the dummy microphone was placed to the centre because it was the best way to test the use of binaural sound and pick up a difference from the sounds coming from the left and right. XY had to be placed in the centre as it was the best place for mono sound pick up (without having it move with our subjects)
Experiment and Results
The experiment was to have a group of people speak and move in front of the set up to give an impression of a 3D layout in the perspective of mono and stereo sound. Firstly the subjects would begin a conversation that would go back and forth i.e. left to right, then the subjects would walk and talk around the room with this we saw that we had a sense of depth through the microphones as you could hear each person getting louder / quieter as they came closer or further away. The thing that was missing at this point was to have equal volumes that would carry in the same directions but instead we had a mixture of sounds that would range in frequencies that were being recorded.
The conversation that went from left to right worked extremely well as we could hear a clear definition from left to right which gave the sense of a 3D layout of room. Even the mono recordings gave a sense of depth when the conversation moved from different areas. One thing I found was some subjects were louder than other which again gave us more range in sound and a sense of 3D layout.
The difference in microphones also gave great results as the nature of the microphones that were used did produce accurate results. For example, our AB microphones produced the best field of response which was due to the placement and straight projection that they produce. The quality was also louder and clearer which again could be because of their placement as well the nature of cardiod microphones (clear response because of a fixed projection). The down point to this is because of this fixed projection the pick up tends to have deep space and phase problems, a problem that would be less likely with a microphone with 3D response.
The XY microphone produced less of a phase problem and also less cross talk, the problem with this was that the XY works on a mono system so all intentions of a 3D layout were reduced and less responsive. The sound was subtle and almost sounded compressed when compared to the clear sound of the AB mic. The degree system works on 90 – 120 degree system meaning that it will pick up a wide section of a set or room but not a 360 or even 180 layout.
The Dummy head recording produced a mixture of results; it is intended to produce a similar result to the human ear and usually runs on two omni microphones that are inserted into the head of a dummy. The recordings picked up a good surround sound but had less clarity than the AB and had a less subtle touch than the XY. What it did produce was an interesting sound to room and did give a sense of 3D layout with an expanded field of response.
There are a number of microphones out there which all do there own duty but one thing is clear; it is better to have a group of microphones that relying on one. Another thing is that to record an entire 3D layout is exceptionally hard due to deep spaces and reverbs off of walls an objects and it is seemly more obvious to me why the use of sound booths and software is extremely important.
One thing I would have liked to do better is to have mastered the volumes more precisely as there was little time to do this. I feel more time on this would have made for better results and a fairer test. If this experiment ever came about again I now have information to prepare me for this and a better understanding of these types of microphones and where and how to include them. I wish to use AB microphones in a tighter confinement so that there is less space and so that their audio pickup may increase as there is less space to work over it will be good for such things as a a scene in a room or car etc. I know now that the XY microphone is really intended for interviews and is risky for other things such as scenes or the experiment that was just done.