A well-known trick with streaming media is to give priority to audio. For many viewers, video can glitch and frame rate can reduce significantly if audio quality is maintained. Within this constraint, monophonic audio can provide some continuity even when surround sound or stereo sound fails. This requires audio to be encoded as a monophonic channel and a left-minus-right channel but MLP demonstrates that mono, stereo and other formats can be encoded together in this form and decoded as appropriate. How far does this technique go? Well, Ambisonics is the application of LaplaceSpherical Harmonics to audio rather than chemistry, weather simulation or a multitude of other purposes.
Yup. That's it. Record directional sound. Convert it into one channel of omnidirectional sound and three channels of directional sound (left-minus-right, front-minus-back, top-minus-bottom). Apply sines and cosines as required or mix like a pro. The result is a four channel audio format which can be streamed as three dimensional sound, two dimensional sound, one dimensional sound or zero dimensional sound and mapped down to any arrangement of speakers.
Due to technical reasons a minimum of 12 speakers (and closer to 30 speakers) are required for full fidelity playback. This can be implemented as a matrix multiplication with four inputs and 30 outputs for each time-step of audio. The elements of the matrix can be pre-computed for each speaker's position, to attenuate recording volume and to cover differences among mis-matched speakers. (Heh, that's easy than buying 30 matched speakers.) At 44.1kHz (Compact Disc quality), 1.3 million multiplies per second are required. At 192kHz, almost six million multiplies per second are required for immersive three dimensional sound.
Using audio amplifiers, such as the popular PAM8403, it is possible to put 32×3W outputs in a 1U box. This is sufficiently loud for most domestic environments.
High Quality Audio, Part 1
(This is the ninth of many promised articles which explain an idea in isolation. It is hoped that ideas may be adapted, linked together and implemented.)
A well-known trick with streaming media is to give priority to audio. For many viewers, video can glitch and frame rate can reduce significantly if audio quality is maintained. Within this constraint, monophonic audio can provide some continuity even when surround sound or stereo sound fails. This requires audio to be encoded as a monophonic channel and a left-minus-right channel but MLP demonstrates that mono, stereo and other formats can be encoded together in this form and decoded as appropriate. How far does this technique go? Well, Ambisonics is the application of Laplace Spherical Harmonics to audio rather than chemistry, weather simulation or a multitude of other purposes.
After getting through all the fiddly stuff like cardiods, A-format, B-format, UHJ format, soundfield microphones, higher order Ambisonics or just what the blazes is Ambisonics? we get to the mother of all 3D sound formats and why people buy hugely expensive microphones, record ambient sounds and sell the recordings to virtual reality start-ups who apply trivial matrix rotation to obtain immersive sound.
Yup. That's it. Record directional sound. Convert it into one channel of omnidirectional sound and three channels of directional sound (left-minus-right, front-minus-back, top-minus-bottom). Apply sines and cosines as required or mix like a pro. The result is a four channel audio format which can be streamed as three dimensional sound, two dimensional sound, one dimensional sound or zero dimensional sound and mapped down to any arrangement of speakers.
Due to technical reasons a minimum of 12 speakers (and closer to 30 speakers) are required for full fidelity playback. This can be implemented as a matrix multiplication with four inputs and 30 outputs for each time-step of audio. The elements of the matrix can be pre-computed for each speaker's position, to attenuate recording volume and to cover differences among mis-matched speakers. (Heh, that's easy than buying 30 matched speakers.) At 44.1kHz (Compact Disc quality), 1.3 million multiplies per second are required. At 192kHz, almost six million multiplies per second are required for immersive three dimensional sound.
For downward compatibility, it may be useful to encode 5.1 surround sound, 7.1 surround sound with Ambisonics. Likewise, it may be useful to arrange speakers such that legacy 5.1 surround sound, 7.1 surround sound, 11.1 surround sound or 22.2 surround sound can be played without matrix mixing.
Using audio amplifiers, such as the popular PAM8403, it is possible to put 32×3W outputs in a 1U box. This is sufficiently loud for most domestic environments.
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