User's Manual Part 1

Nomad User’s Manual Chapter 7 – Monitoring a Test in Progress

7.2 Manual Volume Adjustment (Voice Quality Testing)

Although Spirent recommends running the Auto-Level Assist Wizard (see Section 5.2.5) prior to

Voice Quality testing to find optimal downlink and uplink volume settings, manual volume

adjustment may be necessary to fine-tune the results. Manual volume adjustment may be used in

lieu of Auto Level Assist for analog connections, and must be used in the case of a Bluetooth

connection. Auto Level Assist is not available for Bluetooth

7.2.1 Manual Downlink Volume Adjustment

Downlink volume can be adjusted manually in two fashions:

 Using the handset’s volume control.

 Using the Settings → Levels tab during testing to adjust the Input Level for the channel of

interest.

Spirent Communications strongly recommends testing with the handset volume set one level below

the maximum, and making further adjustments using the Input Level controls.

7.2.1.1 Downlink Volume Adjustment for Bluetooth Connections

In most cases, volume adjustment is not necessary for a channel using a Bluetooth connection.

 In cases where the downlink insertion gain or attenuation for a Bluetooth channel is very

far from 0 (roughly less than -8 dB for insertion gain or greater than 8 dB for attenuation)

the Input Level may be adjusted on the Levels tab by moving the slider one or two notches

to the right.

 The slider should be kept within the Normal Operating Range.

 If MOS deteriorates after the adjustment, return the Input Level to the original value.

Figure 7-22 - Bluetooth Volume Controls

Volume adjustment for a Bluetooth connection operates differently that for an analog connection. Over a

Bluetooth connection, Nomad captures a digital representation of what the handset manufacturer intended to

be sent rather than the incoming voice sample. Instead of having an analog signal that can be amplified

directly, the digital signal must be amplified by changing the received bit representation. The leading bits of

the 16-bit representation are removed to make the remaining signal “louder”. This logarithmic scaling of the

digital signal does not provide the precision available when fine-tuning an analog signal.