Line spectrum frequencies (LSFs) are commonly used in the domain of speech coding as means of representing prediction filters. Quantization of these parameters needs evaluation of spectral distortion. The exact equation giving distortion is presented here using only LSFs. A simplified equation is also proposed as a good approximation.

Minimum shift keying and offset QPSK are two well-known modulations which can be interpreted as a set of time/phase-shifted AM pulses. We show in this paper that any constant amplitude binary phase modulation can also be expressed as a sum of a finite number of time limited amplitude modulated pulses (AMP decomposition). New methods for computing autocorrelation and power frequency spectrum are derived, which give very simple results for half-integer index modulations. We also show that the signal can be built with good accuracy using only one optimized pulse ("main pulse"). This synthesis is particularly satisfactory for modulations that have good spectral characteristics and/ or low index.