Real-Time Vocoder

Real-Time Vocoder

Last updated: September 1, 2009

This section is only applicable to the lab applications and the test application with a required feature license.

Overview

The real-time vocoder allows you to perform the audio test in two aspects:

Real-Time Encoding and Decoding

The real-time vocoder functionality allows you to perform the functional test for the analog voice capability of the mobile station when the Operating Mode of the real-time vocoder is set to Normal :

  • the test set can real-timely encode the analog audio signal applied at the test set's AUDIO IN connector using the appropriate vocoder algorithm (depending upon the selected voice service option) and then sends the encoded audio frames to the mobile station. See A Simplified Signal Flow for Real-Time Encoding .
  • Also, the test set can simultaneously decode the encoded audio frames that is received on the traffic channel using the appropriate vocoder algorithm (depending upon the selected voice service option) and then converts to an analog signal output at the test set's AUDIO OUT connector. See A Simplified Signal Flow for Real-Time Decoding .

A Simplified Signal Flow for Real-Time Encoding

A Simplified Signal Flow for Real-Time Decoding

Vocoder Calibration

The real-time vocoder functionality allows you to calibrate the audio output gain, audio input gain and internal codec loopback gain of the test set when the Operating Mode of the real-time vocoder is set to Calibration .

  • Audio Output Gain Calibration

    The audio output gain calibration is performed when the Calibration Type is set to Audio out Path . The test set sends a full scale sinewave to the AUDIO OUT port. The audio output gain can be determined by measuring the output analog signal.

    The audio output gain calibration result helps to perform the acoustic measurements of the mobile station, for example, the sending sensitivity frequency response.

    Audio Output Gain Calibration
  • Audio Input Gain Calibration:

    You can get the audio input gain of the test set in two ways:

    • Option 1: Set the Calibration Type to Audio In Path . The test set samples the input signal from the AUDIO IN port and loops them back to the AUDIO OUT port via the DAC. If an audio output path calibration has already been done, the audio input gain can be derived from the loopback gain and the audio output gain.
    • Option 2: Set the Calibration Type to Audio Out Path , looping the full scale sinewave from the AUDIO OUT port to the AUDIO IN port. As the audio output gain can be obtained by audio output path calibration, the audio input gain can be determined by reading the Encoder Headroom

    The audio input gain calibration result helps to perform the acoustic measurements of the mobile station, for example, the receiving sensitivity frequency response.

    Audio Input Gain Calibration
  • Internal Codec Loopback gain Calibration

    The internal codec loopback gain calibration is performed when the Calibration Type is set to Internal Codec. The test set samples the input signal from the AUDIO IN port, encodes the samples with the voice encoder and loops them back to the voice decoder, then sends the signals to the AUDIO OUT port via the DAC.

    The internal codec loopback gain calibration result helps to perform the acoustic measurements of the mobile station, for example, the echo loss.

    Internal Codec Loopback gain Calibration

Setting Real-Time Vocoder Parameters

The following parameters can be set from the Real-Time Vocoder Parameters menu. To access the Real-Time Vocoder Parameters menu, see How Do I Use Real-Time Vocoder? .

Real-Time Vocoder Headroom Information

The following results are displayed on the Real-Time Vocoder Information window when a voice call is established and the test set is in the real-time vocoder mode.

Operating Consideration

Related Topics


How Do I Use Real-Time Vocoder?

CALL:RTVocoder