5.3.1 Pre-emphasis

26.2903GPPAudio codec processing functionsExtended Adaptive Multi-Rate - Wideband (AMR-WB+) codecRelease 17Transcoding functionsTS

The input (mono) signal to the core ACELP/TCX encoder is first pre-processed through a high-pass filter. Then, a first-order, fixed pre-emphasis filter is applied with transfer function:

This pre-emphasis filter reduces the signal energy at low frequency and increases the signal energy at high frequency. The result is a signal with a less spectral dynamics, which enhances the resolution of LPC analysis. This is particularly important in fixed-point implementations.