Bluetooth Headset Test Sequence

The purpose of this sequence is to test a Bluetooth headset using a mixture of analog and digital channels

Introduction

The purpose of this sequence is to test a Bluetooth headset using a mixture of analog and digital channels. First, a Multitone stimulus is created with SoundCheck, played back over the Bluetooth headset (at 8 kHz) and recorded by a head and torso simulator’s ear (at 44.1 kHz). Then the same Multitone stimulus is played back through the head and torso’s mouth simulator (at 44.1 kHz) and recorded via the Bluetooth headset (at 8 kHz).

Due to inaccuracies of clock frequency, the Bluetooth device playback sampling rate is often slightly different than it is specified. Therefore, in SoundCheck, the Recorded Time Waveforms are frequency shifted to correct for the inaccurate sampling rate. The exact device playback sampling rate is displayed.

Analysis requires that the stimulus and response waveforms be at the same sampling rate. On the receive side an 8 kHz stimulus is sent and is recorded at 44.1 kHz. In this case the stimulus waveform is upsampled to 44.1 kHz before analysis. On the send side, a 44.1 kHz stimulus is sent and is recorded at 8 kHz. In this case the recorded time waveform is upsampled to 44.1 kHz before analysis.

The analysis is then performed by comparing the original stimulus to the played back stimulus, using a cross-spectrum technique that provides the Frequency Response and Non-Coherent Distortion. Post processing is then used to calculate the Total Non-Coherent Distortion and the Average Sensitivity.

Required Software

• 2020 – Multitone

Required Hardware

• Head and torso simulator – B&K HATS or similar
• Bluetooth transceiver – Portland Tool & Die BTC-4148 or similar
• Audio Interface – Listen AudioConnect or Similar
• Microphone power supply – Listen SoundConnect or similar

Setup Diagram

Hardware Setup and Calibration

By default, SoundCheck’s BT Headset Mic and BT Headset Signal Paths are assigned a digital unity-cal sensitivity value (1 FS/FS). Alternately, calibrated device files files that conform to the AES17 Standard are available in SoundCheck.
AES17 input sensitivity: 0.707 FS/FS
AES17 output sensitivity: 1.414 FS/FS

Receive Path

1. Connect ear output to an appropriate microphone power supply.
2. Connect the output of the microphone power supply to your audio interface
3. Calibrate the ear simulator using a microphone calibrator and SoundCheck’s microphone calibration
   sequence.

Send Path

1. Calibrate the amplifier according to the instructions in the SoundCheck manual.
2. Connect the output of the amplifier to the input of the mouth simulator.
3. Connect the Output 1 of the audio interface to the amplifier.

General

1. Connect and configure your Bluetooth®
   transceiver (e.g. Portland Tool and Die BTC-xxxx)
2. Pair the Bluetooth® headset with the Bluetooth®
   transceiver.
3. The Bluetooth®
   device sampling rate is set to 8 kHz and the audio interface sampling rate is set to
   44.1 kHz.

Get Sequence

This sequence suite is available in the Sequences folder of your SoundCheck installation.