6.2.2 High-pass filtering and up-scaling (all modes)

26.0903GPPAdaptive Multi-Rate (AMR) speech codecMandatory speech CODEC speech processing functionsRelease 17Transcoding functionsTS

The high-pass filter serves as a precaution against undesired low frequency components. A filter cut-off frequency of 60 Hz is used, and the filter is given by

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Up‑scaling consists of multiplying the post‑filtered speech by a factor of 2 to compensate for the down‑scaling by 2 which is applied to the input signal.