How is an analog audio measurement made?
The analog audio measurement can measure Audio Level (V), SINAD (dB), Distortion (%), and Audio Frequency. Measurements are made through the test set's front panel AUDIO IN connectors. When measuring a mobile's audio output, the audio signal may come from either an acoustic coupler or from a test interface connection to the mobile's audio circuitry.
SINAD is one of four measurements available from the Analog Audio measurement. However, SINAD measurements are not typically made when testing GSM mobiles but are more common when testing AMPS or analog mobiles.
See
Analog Audio Measurement Block Diagram
.
The AUDIO IN connectors feed the inputs to a floating-input differential amplifier, with each input having an impedance of about 100,000 ohms to chassis ground. For best noise immunity, connect the audio signal and its ground reference to the two input ports through shielded coaxial cables, or input the signal to the AUDIO IN HI connector and ground the AUDIO IN LO connector's center contact.
SINAD/Distortion State
Select On or Off to enable or disable the SINAD and Distortion measurements. This can be done remotely using the
SETup:AAUDio:SDIStortion:STATe
. When On, these measurement results are displayed on the screen below the Audio Level measurement. The SINAD/Distortion Fundamental Frequency must be entered to specify the audio frequency for the measurement (range: 100 Hz to 10 kHz).
Audio Frequency State
Select On or Off to enable or disable the analog audio frequency measurement.
Filter Type
-
None - no filtering is provided (default).
-
100 Hz BW BPF - The 100 Hz BW Band Pass Filter (Tunable) setting is available when this filter is selected, and can be set in the range of 200 Hz to 20 kHz.
-
C-Message - This type of filter is typically used when testing AMPS or other analog mobiles, and not GSM mobiles.
-
50 Hz to 15 kHz
-
300 Hz to 15 kHz
Detector Type
Select either Peak or RMS (default) for making and displaying an analog audio level measurement (does not affect other measurements). The type of detector selected is displayed next to the Audio Level measurement results. A 1-volt rms sinewave input signal would measure 1.414 V
Peak
when the Peak detector is used. A 1-volt peak input signal would measure 0.707 V
RMS
when the RMS detector is used.
Expected Peak Voltage
The Expected Peak Voltage sets the analog audio clipping level and must be set. This voltage is always the
absolute peak
audio input signal voltage expected at the AUDIO IN connectors, and must be in the range of 7.07 mV
peak
(5 mVrms) to 20 V
peak
. Remember, measuring a 1-volt rms sinewave input signal would require a 1.414 V
peak
expected voltage value to avoid clipping (over-driving) the input.
De-Emphasis State
Set to On or Off (default) to enable or disable 750 microsecond de-emphasis.
Expandor Reference Level
Set value from 10 mV/kHz to 10 V/kHz, or Off (default). Entering a numeric value automatically turns the state to On. Entering Off disables the expandor (state = Off).
Trigger Source
Analog audio measurements use immediate triggering and are continuously re-triggered each time the Trigger Arm parameter is set to Continuous. Trigger timing is independent of any mobile protocol signaling.
