Multi-tone Audio Measurement Description

Last updated: December 3, 2008

This measurement is not applicable to GPRS or EGPRS.

You can use the multi-tone audio measurement to verify the performance of a mobile station's speaker and microphone. This is made possible by the two measurement modes available: downlink and uplink. Audio level, frequency response, and distortion results are available for both modes.

In both modes, there is an audio stimulus, referred to as the "Generator", and an audio analysis, referred to as the "Analyzer". The Generator is a 20 tone source. Presets are provided, which contain frequency and level setting for all 20 tones, or you can specify the frequency and level for each tone. You can choose to have the Analyzer tuned to the same frequencies as the Generator, or you can configure the Analyzer separately.

How is a multi-tone audio measurement made?

The multi-tone audio measurement measures Audio Level (V), SINAD (dB), Distortion (%), and Audio Frequency. 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.

Downlink Measurement Mode

The downlink measurement mode is used to test the mobile station's speaker quality. The tones from the Generator are encoded and sent to the mobile station over the RF link. The mobile station decodes the audio and sends it to the speaker. The audio signal travels through an acoustic coupler to the test set's AUDIO IN port and then to the Analyzer. Measurement results are available for each tone either graphically from the test set's front panel or programmatically using a GPIB query.

Considerations when making a downlink multi-tone audio measurement

The Speech TCH parameter must be set to Multi-Tone for downlink measurements. Setting the speech type to Multi-Tone connects the multi-tone generator to the encoder and ensures the audio signal gets placed on the RF link.

The Expected Audio In Peak Voltage should be set appropriately to avoid over or under range errors.

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.

Uplink Measurement Mode

The uplink measurement mode is used to test the mobile station's microphone quality. The Generator sends the audio tones to the test set's AUDIO OUT port. An acoustic coupler is used to connect the AUDIO OUT port to the mobile station's microphone. The mobile station encodes the audio signal and transmits it back to the test set using the RF link. The test set decodes the audio signal and sends it to the Analyzer. Measurement results are available for each tone either graphically from the test set's front panel or programmatically using a GPIB query.

Considerations when making an uplink multi-tone audio measurement

The Speech TCH parameter must be set to None for uplink measurements. This ensures there is no downlink signal, which would cause bad measurement results.

You should adjust the downlink Generator levels as high as possible to achieve a strong signal on the uplink. This will help prevent the low level portions of the signal from being buried in the noise floor. The downlink Generator level upper limits are dynamic, depending on the generator frequency configuration. You can see this difference when a call is connected and audio is being supplied to the mobile station's microphone. For example, the preset Multi-tone 100 has a lower crest factor and therefore allows the total downlink generator to be set to a higher level than the Multi-tone 140, whose crest factor is larger and therefore would cause signal level peaks which exceed the hardware limitations if it's total limit is set too high.

SINAD/Distortion Measurements

When the SINAD/Distortion State is ON, the test set returns SINAD, Distortion, Audio Level, and Audio Frequency results for audio tone one. In this mode, it is also possible for you to make a distortion level when no tone is being generated. This allows you to detect spurs from the mobile station.

Difference between Multi-tone Audio and Audio Analyzer SINAD/Distortion measurement.

The SINAD/Distortion measurements used by the Multi-tone Audio instrument and the Audio Analyzer use the same algorithms. The primary difference is the Multi-tone Audio instrument allows you to make these measurements on audio that has been sent to the test set over RF instead of only through the AUDIO IN BNC connectors.

Measurement Parameters

Measurement Setup Parameters

Multi-Measurement Count - (See Statistical Measurement Results .)
Measurement Mode - Controls whether measurements are made on the downlink or uplink.
Analyzer 0 dB Reference Mode - Controls the reference to be used when making audio level measurements. The Analyzer Reference Tone is used to specify a reference other than 0 dB if this parameter is set to Relative .
Analyzer Reference Tone - The number of the audio tone to be used as the reference when making relative measurements. The Analyzer 0 dB Reference Mode must be set to Relative for this parameter to be active.
Analyzer Downlink Reference Level - The reference level used when making absolute measurements on the downlink. The Analyzer 0 dB Reference Mode must be set to Absolute and the Measurement Mode must be set to Downlink for this parameter to be active.
Analyzer Uplink Reference Level - The reference level used when making absolute measurements on the uplink. The Analyzer 0 dB Reference Mode must be set to Absolute and the Measurement Mode must be set to Uplink for this parameter to be active.
Expected Peak Voltage - The Expected Peak Voltage sets the 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.
Device Settling Time - The amount of time allowed to lapse after setting the level and frequency before triggering a measurement.
SINAD/Distortion State - Select On or Off to enable or disable the SINAD and Distortion measurements. This can be done remotely using the SETup:MTAudio:SDIStortion:STATe . When On, these measurement results are displayed on the screen instead of the frequency response graph. Only tone one should be active when making the SINAD/Distortion measurement. All other tones should be turned off.
Trigger Arm - (See Trigger Arm (Single or Continuous) Description ) Multi-tone 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.
Measurement Timeout - (See Measurement Timeouts .)

Multi-Tone Audio Generator Parameters

Multi-Tone Audio Generator Frequencies

Preset Frequencies To - Allows you to select a preset frequency configuration for the 20 available audio tones.
Audio Tone <n> Frequency - Allows you to turn on each audio tone individually and specify the frequency associated with it.

Multi-Tone Generator Uplink Levels

Multi-Tone Audio Total Level - Sets the total RMS audio output level, to be distributed evenly among all active frequencies. This setting is dynamic, depending on the active frequencies. See Considerations when making an uplink multi-tone audio measurement for more explanation.
Audio Tone <n> Level - Allows you to turn on each audio tone individually and specify the level associated with it.

Multi-Tone Generator Downlink Levels

Multi-Tone Audio Total Level - Sets the total percentage audio output level, to be distributed evenly among all active frequencies. This setting is dynamic, depending on the active frequencies. See Considerations when making a downlink multi-tone audio measurement for more explanation
Audio Tone <n> Level - Allows you to turn on each audio tone individually and specify the level associated with it.

Multi-Tone Audio Analyzer Parameters

Multi-Tone Analyzer Frequencies

Use Multi-Tone Generator Frequencies - Controls the coupling between the generator frequencies and the analyzer frequencies. If the setting is off, you must specify the frequencies for the analyzer to use.
Audio Tone <n> Frequency - Allows you to turn on each analyzer tone individually and specify the frequency associated with it.

Multi-Tone Audio Level Limits

Controls the upper and lower limits for each audio tone. These settings are used to determine if the measured audio levels for each tone pass or fail.

Measurement Results

Integrity Indicator - (See Integrity Indicator .)
Multi-Tone Audio Level - This is the frequency response. The measurement reports the average RMS level for each of the 20 audio tones that are turned on. The results are displayed in a bar graph on the test set's front panel screen.
Multi-Tone Audio Frequency Response Mask - Indicates a pass or fail for each of the 20 audio tones that are turned on. On the test set's screen, the bar graph for audio tones which fail the mask are displayed in red.
Distortion - The measured distortion of audio tone one. The SINAD/Distortion state must be turned on for this measurement result to be available.
SINAD - The measured SINAD for audio tone one. The SINAD/Distortion state must be turned on for this measurement result to be available.
Audio Level - The measured audio level for audio tone one. The SINAD/Distortion state must be turned on for this measurement result to be available.
Frequency - The measured frequency for audio tone one. The SINAD/Distortion state must be turned on for this measurement result to be available.