26.4453GPPCodec for Enhanced Voice Services (EVS)Detailed algorithmic descriptionRelease 15TS
A first-order high-pass filter is used to emphasize higher frequencies of the input signal and it is given by
where is the pre-emphasis factor which is set to 0.68. The input signal to the pre-emphasis filter is and the output signal is denoted .
If ACELP core is selected for WB, SWB or FB signals at bitrates higher than 13.2 kbps (see subclause 5.1.16), its internal sampling rate is 16kHz rather than 12.8kHz. In this case, the pre-emphasis is re-done at the end of the pre-processing chain, on with . The resulting signal is denoted .
If MDCT-based TCX is selected for SWB or FB high-rate LPC configurations, is used as pre-emphasis factor when pre-emphasis is applied to signals at a sampling rate higher than 16kHz.