Receive Loudness Rating with ITU Real Speech Test Sequence
The purpose of this sequence is to measure the Receive Loudness Rating (RLR) following the ITU-T P.79 standard using a Free Field microphone.
Introduction
The purpose of this sequence is to measure the Receive Loudness Rating (RLR) following the ITU-T P.79 standard using a Free Field microphone. First, real speech from the ITU-T P.501 standard is sent to the Device Under Test (DUT) speaker by an electrical interface. The Free Field microphone captures the DUT‟s speaker response. SoundCheck calculates the frequency response and then RLR based on that recording.
This sequence is for use with speakerphone / handsfree devices and a Free Field microphone only. There are other example sequences for RLR with HATS for speakerphones and RLR with handset / headset devices.
Loudness Rating is a fundamental metric used in telephony. Loudness ensures that the levels passed between the DUT and the network match. If the levels do not match the potential for voice signals to become clipped, distorted, or under ranged becomes a major issue and will lead to poor voice quality reproduction. All communication devices (e.g. mobile phones, landline phones, wired headsets, Bluetooth speakerphones, conference call phones) must use Loudness Rating to set the level of the DUT correctly.
Required Software
- 2007 – Telephone Loudness Rating
- 2033 – Active Speech Level
Required Hardware
- Free Field Measurement Microphone
- Audio Interface – Listen AmpConnect or similar
- Digital Interface – Virtual Audio Cable plus Reference Softphone (e.g. Linphone, Bria 5) for VoIP phones, Portland Tool & Die BTC-4148 for Bluetooth devices, USB port on PC for USB devices, etc
Setup Diagram
Hardware Setup and Calibration
- In the Hardware -> Audio tab be sure to use a Vp that follows your codec overload point and A/D = Analog. The below screenshot uses a Vp of 1.572, which is the overload point of an “A Law” codec.
- A special Output Signal Path is used “Receive (SC to DUT)”. This is the electrical signal presented to the DUT‟s speaker. This Signal Path must use the Receive (DUT to SC) calibrated device file which applies 1V/V sensitivity and dB reference 775 mV.
- The Input Signal Path is Reference Mic. Calibrate your microphone before running the sequence.
- Note, the stimulus used in this sequence is set to -16 dBm0 Active Speech Level.
Get Sequence
This sequence is included in the Sequences folder of your SoundCheck installation.
