APPENDIX – Tuning the Loudspeaker#

Tuning the XVF3800 to optimise loudspeaker performance with the XK-VOICE-SQ66 development kit involves four steps:

# Optionally adding EQ to the loudspeaker frequency response, # Setting the maximum loudspeaker volume, # Retraining the non-linear matrix in the XVF3800 audio pipeline, # Rebuilding the XVF3800 executable image.

Adding EQ to the Loudspeaker Frequency Response#

Many communication specifications expect roll-off at low frequencies, e.g., as shown below:

../../../../_images/BB_FrequencyResponseMask.png

Small loudspeakers often have a boost at 100-200 Hz to add more bass to the sound. This may need to be removed to meet the specification, e.g., by adding a low shelf to reduce the response by 6 to 10 dB. The steps below describe the process:

# Use the Room EQ Wizard (REW) to determine the filtering to add.

Start by measuring the loudspeaker response at a close distance, then add EQ filters to shape the response as required.

# Use the Audio EQ Cookbook equations to generate biquad coefficients. # Convert these coefficients into the format used with the Texas Instruments TLV320DAC3101 Digital to Analogue Converter. # Set the biquad in the TLV320DAC3101 DAC on the XK-VOICE-SQ66 development kit using its page 8 registers.

Table 6-14 of the TLV320DAC3101 datasheet provides some useful details.

Note

The Python script modules/bsp/dac/dac3101/dac3101_biquad_converter.py provides support for generating the biquad coefficients and converting them into the form required by the TLV320DAC3101 Digital to Analogue Converter.

Setting the Maximum Loudspeaker Volume#

See Speaker Operation for information on setting the loudspeaker volume. When using the TLV320DAC3101, registers 36 (0x24) and 37 (0x25) in page 1 may require new values. Tables 6-24, 6-103, and 6-104 of the TLV320DAC3101 datasheet provide useful details.

Remaining Steps#

Check the mic level with the new loudspeaker, see Microphone Gain. To retrain the non-linear matrix in the XVF3800 audio pipeline, see Tuning the Non Linear Model. To rebuild the XVF3800 executable image, see Building the Application Firmware.