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3D sound reconstruction is the application of reconstruction techniques to 3D sound localization technology. These methods of reconstructing 3D sound can be used to recreate sounds to match natural environments and provide spatial cues of the sound source. They also see applications in creating 3D visualizations on a sound field to include physical aspects of sound waves including direction, pressure, and intensity.
Motivation and Applications
When reconstructing recorded 3D audio and visualizing sound fields, sound localization and reconstructing the reverberation and sound pressure are critical to produce robust and natural-sounding audio. There are various techniques to process sound so that the spatial cues can be reproduced when reconstructing sound. This technology sees a demand in entertainment as audiences look for the ambience of a live performance reproduced through their speakers. Reconstructing a 3D sound field also becomes critical in military applications where visualizing pressure in a 3D sound field can help determine location of sound sources. The techniques used for sound field reconstruction are similar to those used to reconstruct sounds to detect solid objects, but applied to air to detect changes in pressure and sound intensity.[1]
Problem Statement and Basic Concepts
Various methods of determining the location of a sound source have been determined through 3D sound localization which determines the location based off a variety of attributes and makes use of multiple microphone arrays, binaural hearing methods, and HRTF(Head-related transfer function). These methods are coupled with other signal processing techniques to measure the impulse response over lengths of time to determine the intensity components in different directions. Combining intensity of sound with direction, a 3D sound field can be determined and various physical qualities that create the resulting changes in intensity can be reconstructed
Methods
Reverberation Reconstruction
The reverberation reconstruction is done by a four-point microphone setup to measure reverberations in the sound stage. Each microphone measures impulse response using a Time-Stretched Pulse(TSP) as the signal. This method has a disadvantage as measurements taken are assumed to include only one sound, while real-life reverberations include various sounds. The measured impulse response include information for various time frames with various sound sources. The data obtained by measuring various sound sources at different time frames can be applied to the 5-speaker sound system. The new system convolves the HRTF with the impulse response determined by the reverberation reconstruction method. From this convolution, the energy is adjusted to be applied to the original time frame, and a delay is applied to the result. The convolution and delays are applied to all of the sound source data taken and summed. The resulting signal contains the reverberation in the reconstructed signal when replayed to listeners. The advantage of this method is that the signal that is reconstructed makes localization improved, as the direction of the sound source can be more easily perceived by the listener. This technique is also great for improving the naturalness of sounds which many people consider as important when using speakers for entertainment. A drawback of this method is that the assumption of a single sound source, coupled with adding all the different values does not improve listeners perception of the size of the room. Directionality is improved while distance is not.[2]
Laser Projections
In regards to a sound field, sound waves cause changes in air density to reflect possible changes in sound pressure caused by intensity of the source. A visual reconstruction of the sound field can be reproduced through the usage of a signal processing technique called,Tomography. The reconstruction of the sound field through projections is a alternative method that does not need the usage of various microphones to determine separate impulse responses. Instead sound pressure is measured using a laser Doppler vibrometer and all values on the path of the laser can be measured. This saves the number of points needed with using an array of microphones [1]
Near-Field Acoustical Holography
References
- ^ a b Oikawa; Goto; Ikeda; Takizawa; Yamasaki (2005). "Sound field measurements based on reconstruction from laser projections". IEEE International Conference on Acoustics, Speech, and Signal Processing Proceedings. (ICASSP '05). 4: iv/661-iv/664. doi:10.1109/ICASSP.2005.1416095.
- ^ Tanno; Saiji; Huang (2013). "A new 5-loudspeaker 3D sound system with a reverberation reconstruction method". Awareness Science and Technology and Ubi-Media Computing (iCAST-UMEDIA), 2013 International Joint Conference on: 174–179. doi:10.1109/ICAwST.2013.6765429.
- ^ Ohbuchi; Mizutani; Wakatsuki; Nishimiya; Masuyama (2009). "Reconstruction of Three-Dimensional Sound Field from Two-Dimensional Sound Field Using Optical Computerized Tomography and Near-Field Acoustical Holography". Japanese journal of applied physics. 48 (7): 07–07.