USING SPECTRAL DISTANCE MEASURES FOR VOCODER ERROR DETECTION
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-12
Digital radio systems employ vocoders to reduce the total number of bits needed to transport the voice information. For example, the ASTRO radio sys- tem uses VSELP a vocoder which encodes speech as a set of parameters representing the energy, pitch, excitation, and vocal tract response of the original speech. Under low signal conditions, this voice infor- mation will become corrupted by bit errors, resulting in degraded or unintelligible speech quality. Forward error correction is therefore used to lessen the effect of errors, with the transmitter adding extra parity bits to the VSELP information and the receiver using these bits to correct bit errors that may have occurred. Due to bandwidth limitations, the error correction codes are generally not strong enough to correct all of the bit errors that occur in normal operation. Because the error correction decoding will some- times fail to correct bit errors, it is desired to have an algorithm that will detect this situation and engage a process to mitigate its effects.