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Future Cinema – Binaural Sound – Digital Sound Recording

Digital Sound Recording

For our group project we are investigating methods of digital sound recording using both a Digital Audio Recorder (Fostek FR-2LE field recorder ) and recording directly to a MacBook Pro’s line input.

Digital Sound Recording direct to MacBook Pro line input

Fig 1.0 Digital Sound Recording direct to MacBook Pro line input

Using one of the University Recording Studios we set up the Dummy Head with the binaural microphones inside a soundproof room. The microphones were connected directly to the Mac’s line input. To record the audio I used Audacity a free audio editor and digital sound recorder which is available for both Windows, PC and Mac computers. I made one change to the programs preferences changing the input source from internal microphone to line input. As we were using a sound booth I was able to monitor the recording using the Mac’s internal speakers.

I immediately identified a number of limitations to using the sound booth, primarily there was little space to move around the room, which was a necessity for the script and groups overall concept but in counterbalance the audio recordings that were produced were of excellent quality.

[youtube.com/watch?v=4R38s3c9Unw]
Sennheiser ME66 Microphones - Surround Sound Recording Setup

Fig 2.0 Sennheiser ME66 Microphones - Surround Sound Recording Setup

The next step in the audio recording tests was to relocate to one of the Universities Film Studios. With the benefit of the much greater floor space we setup again the dummy head, but in addition we also positioned 4 directional microphones in pairs linked to two Fostek FR-2LE field recorders that is a Digital Audio Recorder. This in effect gave us 4 channels to record on, that is Left Front, Right Front then Left Back and Right Back.

The positioning choice made for these microphones initially seemed obvious with one set in each corner of the space and directed towards the centre aiming as close as possible at the dummy’s head. This however did not provide the sound (Channel) separation we were looking for.

There was considerable crossover between the channels, for this reason we re-positioned the microphones around the dummy head pointing away towards the corners of the studio space. This proved to be a real improvement when considering just channel separation but it created its own problems by physically obstructing access to the dummy head and effecting the binaural recording process.

Sennheiser ME66 Microphones - Surround Sound Recording Setup 2

Fig 3.0 Sennheiser ME66 Microphones - Surround Sound Recording Setup 2

As a final change in the microphone position we tried relocating the microphones to the corners of the studio space, pointing the microphones downward at floor at a 45 degree angle, the microphone stands were extended raising the microphones 3.5 metres above the floor. In effect each microphone was covering a quadrant of the studio floor space. Results proved to be indeterminate using this setup over the original microphone positioning and so in conclusion of these test recordings it was felt that the best results had been obtained with the microphones positioned centrally, around the dummy head and facing outwards to the four corners of the studio space.

Zoom H2 Handy Recorder

Fig 4.0 Zoom H2 Handy Recorder

Based on these tests the best setup for recording surround sound appears to be to have four microphones combined into one recording device centrally located. An example of such a device is the Zoom H2 Handy Recorder.

Microphone Choices

Based on the audio recordings made on the night we came to realise that our choice of microphone which seemed obvious at the time may not have been the correct choice. Our original specification for microphones choice were that in order to get the separation required for the 5.1 Surround Sound audio recording we would require a directional microphone.

Fig 5.0 Polar Pattern Shotgun Microphone

Fig 5.0 Polar Pattern Shotgun Microphone

We used Sennheiser ME66 Microphones which are very sensitive but also very directional and designed to eliminate noises not emanating from the target direction. From the audio recordings we had channel separation but the volume dropped as well as the actor walked into dead spots created by the very directional behaviour of the microphones used. The shot gun microphones we used have a very direction Polar Pattern see Fig 5.0

Fig 6.0 Cardioid Microphone Polar Pattern

Fig 6.0 Cardioid Microphone Polar Pattern

After discussing this with Lecturers we came to realise that a different choice of Microphone may have produced an improved recording. Cardioid microphones seemed to offer the best solution. The shot gun microphones we used have a very direction Polar Pattern see Fig 5.0, as you can see very different to the Cardioid polar pattern (See Fig 6.0 and 6.1 ). All microphones have different characteristics one is called a polar pattern this is the direction and the coverage that the microphone pick up from.

Fig 6.1 Example Cardioid Microphone showing Polar Pattern

Fig 6.1 Example Cardioid Microphone showing Polar Pattern

So a Cardioid microphone (Heart Shaped) will only pick up sound from one direction but has a wider target range. With this microphone we could effectively segment the studio into 4 zones with some overlap so that we still get the channel separation but there would be some overlap so that when the actor walks around the microphones pickup area we would still get the directional change but without such a dramatic volume drop off as they passed between microphone positions.

 

Evaluating the results

The next step will be to evaluate the test recordings that were produced and source another similar location suitable for audio recording, a location which combines the benefits of a sound proof room but with the floor space to be able to setup all the equipment and for the actors to move freely.

An example audio recording from the binaural microphone setup on the night.

Future Cinema – Links to Related Blog Entries

  1. Future Cinema – Project Conclusion
  2. Future Cinema – Sound Effects
  3. Future Cinema – Digital Cinema
  4. Future Cinema – 5.1 Surround Sound
  5. Future Cinema – Binaural Sound – Digital Sound Recording
  6. Future Cinema – 360 Degree Camera Mount
  7. Future Cinema – Learning Agreement (Updated)
  8. Future Cinema – Audio / Film Script 1st Draft
  9. Future Cinema – Binaural Sound Recording
  10. Future Cinema – The Film Pitch
  11. Future Cinema – does it have one?

 

 

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