26.1903GPPAdaptive Multi-Rate - Wideband (AMR-WB) speech codecSpeech codec speech processing functionsTranscoding functionsTS
The high-pass filter serves as a precaution against undesired low frequency components. The signal is filtered through the high-pass filter Hh1(z) and de-emphasis filter Hde_emph(z).
Finally, the signal is upsampled to 16 kHz to obtain the lower band synthesis signal . is produced by first upsampling the lower band synthesis at 12.8 kHz by 5, then filtering the output through Hdecim(z), and finally downsampling it by 4.
(Up-scaling consists of multiplying the output from the high-pass filtering by a factor of 2 in order to compensate the down-scaling at the pre-processing stage.)