APPENDIX – Alternative Tuning Parameters#

The default tuning parameters have been selected such the XK-VOICE-SQ66 development kit will perform well against the Microsoft Teams V5 “Personal Space Speakerphone” specification. Parameters related to the loudspeaker, such as EQ and the non-linear model, are unique to specific loudspeakers. Different gain and AGC settings may also be needed, depending on the requirements of the specification.

In this appendix, alternative tuning parameters for specific loudspeakers and specifications are provided:

  • MS Teams V5 Personal Space Speakerphone using a Logitech Z50 loudspeaker

  • MS Teams V5 Shared Space Speakerphone at 4.5 m using a Genelec 8020 loudspeaker

Personal Space Speakerphone using a Logitech Z50 loudspeaker#

For meeting the Teams Personal Space Speakerphone specification using a Logitech Z50 loudspeaker, the following changes are required:

  • DAC output needs an attenuation of low frequencies using a low shelf filter (280 Hz, -6 dB gain, Q=1.3) to remove the low frequency boost caused by the table under the loudspeaker.

  • Microphone gain can be increased, the Logitech Z50 has a low maximum SPL so this can occur without the risk of clipping the microphone signal.

  • Non-linear model must be trained to match the non-linearities of the Logitech Z50 with this DAC EQ and microphone gain.

  • AGC gain and maximum gain must be adjusted for microphone gain for a speech level of 89 dBSPL at the mouth reference point.

This requires changes to the following files:

  • sources/app_xvf3800/autogeneration/yaml_files/settings_and_defaults/control_param_values.yaml

  • sources/app_xvf3800/nl_model_gen/nlmodel_bin/nlmodel_buffer_override.bin.r16.c40

  • sources/modules/fwk_xvf/modules/bsp/dac/dac3101.c

Copies of these files configured for the Logitech Z50 are included in the folder sources/app_xvf3800/configurations/logitech_z50. Copy each file from the folder to their respective locations listed above. The firmware can then be built using the instructions in Build Process, and flashed to the device.

The Logitech Z50 has no controls, so requires no additional configuration. Simply connect it’s 3.5 mm input cable to the line out on the XK-VOICE-SQ66 development kit.

Shared Space Speakerphone at 4.5 m using a Genelec 8020 loudspeaker#

For meeting the Teams Shared Space Speakerphone at 4.5 m specification using a Genelec 8020 loudspeaker, the following changes are required:

  • XK-VOICE-SQ66 development kit line output must be configured to balanced to match the Genelec 8020 input. This involves setting the DAC registers for differential output mode, see the TLV320DAC3101 datasheet for more details. Note that connecting a balanced output to a stereo input will result in a very small signal level if the channels are summed.

  • Line out volume must be reduced by 1.5 dB to set maximum loudspeaker SPL within limits.

  • DAC output needs an attenuation of low frequencies using a low shelf filter (328 Hz, -10 dB, Q=1.1) to remove the low frequency boost caused by the table under the loudspeaker.

  • DAC output also needs a 150 Hz high pass filter (Q=0.707) applied to reduce loudspeaker bass level. This filter is applied twice.

  • Non-linear model must be trained to match the non-linearities of the Genelec 8020 with this DAC EQ and microphone gain.

  • Slower AGC parameters are needed. This is to avoid collisions with the Teams Client AGC, which is also included in the signal path for the specification. This improves the MOS (Mean Opinion Score) in echo tests with the Teams client.

  • Equalization filter must be applied to the processed output to fit within the send frequency response limits in the specification.

  • A small increase in noise suppression is required to meet test specification.

This requires changes to the following files:

  • sources/app_xvf3800/autogeneration/yaml_files/settings_and_defaults/control_param_values.yaml

  • sources/app_xvf3800/nl_model_gen/nlmodel_bin/nlmodel_buffer_override.bin.r16.c40

  • sources/app_xvf3800/eq_filter_gen/eq_filter_bin/eq_filter_override.bin

  • sources/modules/fwk_xvf/modules/bsp/dac/dac3101.c

Copies of these files configured for the Genelec 8020 are included in the folder sources/app_xvf3800/configurations/genelec_8020. Copy each file from the folder to their respective locations listed above. The firmware can then be built using the instructions in Build Process, and flashed to the device.

To configure the Genelec 8020 loudspeaker, set all the switches on the rear down. The sensitivity control should be set to +6 dB (fully anti-clockwise), which is the quietest setting. An XLR-to-TRS jack cable, with a 6.35 mm to 3.5 mm jack adapter, is required to connect to the line out on the XK-VOICE-SQ66 development kit.