Conventional surround sound is based on using audio compression technology (for example Dolby or Digital AC-) to encode and deliver a multi-channel soundtrack, and audio decompression technology to decode the soundtrack for delivery on a surround sound 5-speaker setup. Additionally, virtual surround sound systems use 3D audio technology to create the illusion of five speakers emanating from a regular set of stereo speakers, therefore enabling a surround sound listening experience without the need for a five speaker setup. The virtual surround systems have many advantages over conventional surround systems. One is a conventional system contain five speakers, each must be positioned properly, wired to the main amplifier or receiver, balanced -daunting task for someone who just wants to watch a good movie. This seminar deals with different methods to produce virtualization of surround sound, especially Real-Time Partitioned Convolution for Surround sound.
Ambiophonics is a method in the public domain that employs digital signal processing (DSP) and two loudspeakers directly in front of the listener in order to improve reproduction of stereophonic and 5.1 surround sound for music, movies, and games in home theaters, gaming PCs, workstations, or studio monitoring applications. First implemented using mechanical means in 1988 [1,2]. Ambiophonics eliminates crosstalk inherent in the conventional “stereo triangle” speaker placement, and thereby generates a speaker-binaural soundfield that emulates headphone-binaural, and creates for the listener improved perception of “reality” of recorded auditory scenes. A second speaker pair can be added in back in order to enable 360° surround sound reproduction. Additional surround speakers may be used for hall ambience, including height, if desired.
In stereophonics, the reproduced sound is distorted by crosstalk, where signals from either speaker reach not only the intended ear, but the opposite ear, causing comb filtering that distorts timbre of central voices, and creating false “early reflections” due to the delay of sound reaching the opposite ear. In addition, auditory images are bounded between left (L) and right (R) speakers, usually positioned at ±30° with respect to the listener, thereby including 60°, only 1/6 of the horizontal circle, with the listener at the center. (It should be noted that human hearing can locate sound from directions not only in a 360° circle, but a full sphere.)
Ambiophonics eliminates speaker crosstalk and its deleterious effects. Using Ambiophonics, auditory images can extend in theory all the way to the sides, at ±90° left and right and including the front hemi-circle of 180°, depending on listening acoustics and to what degree the recording has captured the interaural level differences (ILD) and the interaural time differences (ITD) that characterize two-eared human hearing. Most existing two channel discs (LPs as well as CDs) include ILD and ITD data that cannot be reproduced by the stereo loudspeaker “triangle” due to inherent crosstalk. When reproduced using Ambiophonics, such existing recordings’ true qualities are revealed, with natural solo voices and wider images, up to 150° in practice.
It is also possible to make new recordings using binaurally-based main microphones, such as an Ambiophone [3], which is optimized for Ambiophonic reproduction (stereo-compatible) since it captures and preserves the same ILD and ITD that one would experience with one’s own ears at the recording session. Along with life-like spatial qualities, more correct timbre (tone color) of sounds is preserved. Use of ORTF, Jecklin Disk, and sphere microphones without pinna (outer ear) can produce similar results. (Note that microphone techniques such as these that are binaural-based but without pinna also produce compatible results using conventional speaker-stereo, 5.1 surround, and mp3 players.)
By repositioning speakers closer together, and using digital signal processing (DSP) such as free RACE (Recursive Ambiophonic Crosstalk Elimination [5]) or similar software, Ambiophonic reproduction is able to generate wide auditory images from most ordinary CDs/LPs/DVDs or MP-3s of music, movies, or games and, depending upon the recording, restore the life-like localization, spatiality, and tone color they have captured. For most test subjects, results are dramatic, suggesting that Ambiophonics has the potential to revitalize interest in high-fidelity sound reproduction, both in stereo and surround.
