6.2 High-pass filtering, up-scaling and interpolation

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 H_h1(z) and de-emphasis filter H_{de_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 H_decim(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.)