This paper presents an ARX-LF-based model of speech that is amenable to low-bit-rate quantization and speech modifications directly at the parametric domain. The new model successfully addresses the non-deterministic part of voiced speech by modulating noise with the glottal flow, while unvoiced speech and transients are synthesized by modulating noise with a signal-derived time envelope. The presented work is essentially a high-quality vocoder that can be used for low complexity coding/synthesis/modification of speech suitable for embedded text-to-speech applications.