XVF3800 Channel - ASR - external amplifier

[juniormajor]

as i'm using an HiFiBerry Amp as an external amplifier, i'm testing AEC/ASR options. i don't find the location, where the used channel of the XVF is defined, as in 2.0.7 left channel is post-processed audio, right channel is ASR. Or am i overthinking the config?

[imonlinux]

Hey @juniormajor, the LVA code automatically sets both left and right mic channels to 7 3 instead of the default R 8 0 L 7 3. This was done due to the way soundcard merges the two channels into a single channel which is needed for wake word detection. Through testing, having both channels set to 7 3 (post-processed audio) resulted in better wake word detection and fewer false positives.

This change is initiated by the main.py file (line 157) and committed by xvf3800_led_backend.py (line 41) as this is where the other usb ctl_transfer() logic is performed.

Let me know if this doesn't answer your question.

[juniormajor]

perfect. thx. did you test also to change the channel count on the pi side? or what do you mean by "...the way soundcard merges the two channels..."? further question: as you mention the xmos flashing to be done on a different host than a pi, did it work from the pi at all?

[imonlinux]

Sure thing. The discussion thread linked below has a lot of good detail on how we got to setting the mic profiles. I attempted to flash the xmos using the RPi Zero 2w but it would never complete. I had use my laptop to flash the recover firmware and flash the 2.0.7 firmware again.

LVA opens the XVF3800 input stream at 16 kHz, channels=1 via the soundcard library:

• PipeWire/PulseAudio provides the XVF3800 as a 2-channel source.
• When LVA requests 1 channel, the audio backend automatically downmixes L+R to mono (typically an average/weighted sum) before LVA receives samples.
• LVA then converts that mono float stream to 16-bit PCM and feeds it to the wake-word + satellite audio pipeline.

#45 (comment)

[juniormajor]

1. regarding the "...flash the xmos using the RPi Zero 2w but it would never complete...". After serveral different attempts => with a complete git clone of the xmos repository, the dfu-util works for me also from an pi4 and an pi0. Download with wget,.. doesn't work.
2. as i'm going to use an external amp (and not the xvf itself), is there a poven way for audio loopback/reference input for noise cancelling/AVR/...?

[imonlinux]

Hey @juniormajor, unfortunately I am not very familiar with the inner workings of the XVF3800. I have learned quite a bit from both @cknic @JenniferHatches while getting the XVF3800 working well with LVA. Perhaps they have more insights. The only information that I could quickly find is https://www.xmos.com/documentation/XM-014888-PC/html/modules/fwk_xvf/doc/datasheet/03_audio_pipeline.html

[juniormajor]

Thx - already found/read that. so my quick and dirty trial is a combined pipewire sink (HifiBerry & XVF).

#!/bin/bash
HIFIBERRY_CARD=$(aplay -l | awk -F'[: ]+' '/snd_rpi_hifiberry/{print $2; exit}')
XVF3800_CARD=$(aplay -l | awk -F'[: ]+' '/XVF3800/{print $2; exit}')

if [ -z "$HIFIBERRY_CARD" ]; then
echo "[Error] No HiFiBerry detected!"
exit 1
fi
if [ -z "$XVF3800_CARD" ]; then
echo "[Error] No XVF3800 detected!"
exit 1
fi

if ! pactl list short sinks | grep -q "hifiberry_amp"; then
echo "[Assistant Setup] Loading HiFiBerry Sink..."
pactl load-module module-alsa-sink device=hw:$HIFIBERRY_CARD,0 sink_name=hifiberry_amp sink_properties=device.description="HiFiBerry_Speaker"
else
echo "[Assistant Setup] HiFiBerry Sink already exists."
fi

if ! pactl list short sinks | grep -q "xvf3800_ref"; then
echo "[Assistant Setup] Loading XVF3800 Reference Sink..."
pactl load-module module-alsa-sink device=hw:$XVF3800_CARD,0 sink_name=xvf3800_ref sink_properties=device.description="XVF3800_Reference"
else
echo "[Assistant Setup] XVF3800 Reference Sink already exists."
fi

COMBINED_NAME="assistant_combined"
if ! pactl list short sinks | grep -q "$COMBINED_NAME"; then
echo "[Assistant Setup] Creating Combined Sink (Splitter)..."
pactl load-module module-combine-sink
sink_name=$COMBINED_NAME
slaves=hifiberry_amp,xvf3800_ref
sink_properties=device.description="Assistant_Combined_Audio"
else
echo "[Assistant Setup] Combined Sink already exists."
fi

pactl set-default-sink $COMBINED_NAME
echo "[Assistant Setup] Default Sink set to: $COMBINED_NAME (Outputs to Amp + XVF)"
XVF_SOURCE=$(pactl list short sources | awk '/XVF3800/ && !/monitor/ {print $2; exit}')

if [ -n "$XVF_SOURCE" ]; then
pactl set-default-source "$XVF_SOURCE"
echo "[Assistant Setup] Default Source set to: $XVF_SOURCE"
else
echo "[Warning] Could not automatically find XVF3800 Source name. Please check 'pactl list sources'."
fi

pactl set-sink-volume hifiberry_amp 100%
pactl set-sink-volume xvf3800_ref 100%
pactl set-sink-volume $COMBINED_NAME 100%

echo "[Assistant Setup] Configuration complete!"