06.103GPPFull Rate Speech TranscodingTS
This clause specifies the necessary performance characteristics of the audio parts for proper functioning of the speech transcoder. Some transmission performance characteristics of the RPE‑LTP transcoder are also given to assist the designer of the speech transcoder function. The information given here is redundant and the detailed specifications are contained in recommendation GSM 11.10.
The performance characteristics are referred to the 13 bit uniform PCM interface.
NOTE: To simplify the verification of the specifications, the performance limits may be referred to an A‑ or -law (PCS 1900) measurement interface according to ITU‑T Recommendation G.711. In this way, standard measuring equipments for PCM systems can be utilized for measurements. The relationship between the 13 bit format and the A‑ or -law (PCS 1900) companded shall follow the procedures defined in subclause 1.4.
2.1 Performance characteristics of the analogue/digital interfaces
Concerning 1) discrimination against out‑of‑band signals (sending) and 2) spurious out‑of‑band signals (receiving), the same requirements as defined in ETSI standard TE 04‑15 (digital telephone, candidate NET33) apply.
2.2 Transcoder delay
Consider a back to back configuration where the parameters generated by the encoder are delivered to the speech decoder as soon as they are available.
The transcoder delay is defined as the time interval between the instant a speech frame of 160 samples has been received at the encoder input and the instant the corresponding 160 reconstructed speech samples have been out‑put by the speech decoder at an 8 kHz sample rate.
The theoretical minimum delay which can be achieved is 20 ms. The requirement is that the transcoder delay should be less than 30 ms.