Electrical audio signal processing systems and devices – One-way audio signal program distribution – Public address system
Patent
1987-06-02
1990-05-01
Kemeny, Emanuel S.
Electrical audio signal processing systems and devices
One-way audio signal program distribution
Public address system
381 34, 375122, G10L 500
Patent
active
049225375
ABSTRACT:
An audio signal is initially represented by a series of high-resolution pulse code modulated (PCM) data. A lower rate series of representative values are extracted from the initial series of PCM data. Half of the lower rate is at an intermediate audio frequency so that the lower rate series encodes low frequency components of the audio signal. The PCM data are adjusted by offsetting in accordance with corresponding representative values and are then converted to a floating-point representation by extracting scale factor or exponents. The combination of the series of representative values and the floating-point data provides a rate-compressed representation of the audio signal which is capable of being decoded after transmission or storage to reproduce the audio signal without substantial noise, distortion or loss of dynamic range. The splitting of the audio information between the lower rate series and the adjusted floating-point PCM limits the normally destructive effect that low frequency components of high amplitude have upon high frequency components of relatively low amplitude. In a preferred embodiment, a common offset is determined for each block by computing the arithmetic mean of the maximum and minimum PCM data values for the block and truncating the result, the PCM data are adjusted by subtracting their corresponding common offsets, and a common exponent is determined for the block of adjusted PCM data. For encoding high-fidelity audio, preferably the audio signal is initially represented by a series of 16-bit PCM samples at a rate of at least 36 kilohertz, the block size is chosen to be 16 audio samples, and the encoded and compressed data for each block includes a 160 bit frame consisting of an 8-bit block offset, a 3-bit block exponent, a 5-bit error correction code, and sixteen floating-point values each including eight data bits and one parity bit. This format permits 9 stereo audio channels and frame synchronization to be readily transmitted over a conventional video channel.
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F. Mazada (editor), Electronics Engineer's Reference Book, 5th ed., Butterworths, Boston, Mass., (1983), pp. 51/6-9, 54/21-22, 56/18-23.
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Frederiksen & Shu Laboratories, Inc.
Kemeny Emanuel S.
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