A systematic hybrid analog/digital audio coder

This paper describes a signal coding solution for a hybrid channel that is the composition of two channels: a noisy analog channel through which a signal source is sent unprocessed and a secondary rate-constrained digital channel. The source is processed prior to transmission through the digital channel. Signal coding solutions for this hybrid channel are clearly applicable to the in-band on-channel (IBOC) digital audio broadcast (DAB) problem. We present the design of a perceptually-based subband audio coder, with complexity comparable to conventional coders, that exploits a signal at the receiver of the form y[n]=g[n]*x[n]+u[n], where x[n], g[n], and u[n] denote respectively the source, the impulse response of convolutional distortion, and additive Gaussian noise. Concepts from conventional subband coding, e.g. subband decomposition, quantization, bit allocation, and lossless signal coding, are tailored to exploit the analog signal at the receiver such that frequency-weighted mean-squared error is minimized.