AudioNormalise

There is the ffmpeg-normalize python package.

Also Chatgpt came up with this bash script:

#!/usr/bin/env bash
#
# loudnorm.sh — two-pass EBU R128 loudness normalization with ffmpeg
#
# Usage: ./loudnorm.sh input.wav output.wav
#
# Defaults: I=-16 LUFS, TP=-1.5 dBTP, LRA=11 LU

set -e

INPUT="$1"
OUTPUT="$2"

if [[ -z "$INPUT" || -z "$OUTPUT" ]]; then
  echo "Usage: $0 input.wav output.wav"
  exit 1
fi
echo "Starting $INPUT -> $OUTPUT"

# Target values (change if you want broadcast settings like I=-23, TP=-2)
I=-16
TP=-1.5
LRA=11

# First pass: analyze
JSON=$(ffmpeg -i "$INPUT" -af loudnorm=I=$I:TP=$TP:LRA=$LRA:print_format=json -f null - 2>&1 | grep -A 12 "^\{" )
echo "Got JSON"

# Extract measured values from JSON using jq (if installed)
if command -v jq >/dev/null 2>&1; then
  MI=$(echo "$JSON" | jq -r .input_i)
  MTP=$(echo "$JSON" | jq -r .input_tp)
  MLRA=$(echo "$JSON" | jq -r .input_lra)
  MTHRESH=$(echo "$JSON" | jq -r .input_thresh)
  OFFSET=$(echo "$JSON" | jq -r .target_offset)
else
  # crude grep/awk fallback if jq isn’t available
  MI=$(echo "$JSON" | grep input_i | awk '{print $3}' | tr -d '",')
  MTP=$(echo "$JSON" | grep input_tp | awk '{print $3}' | tr -d '",')
  MLRA=$(echo "$JSON" | grep input_lra | awk '{print $3}' | tr -d '",')
  MTHRESH=$(echo "$JSON" | grep input_thresh | awk '{print $3}' | tr -d '",')
  OFFSET=$(echo "$JSON" | grep target_offset | awk '{print $3}' | tr -d '",')
fi

echo "First pass results:"
echo "  input_i      = $MI"
echo "  input_tp     = $MTP"
echo "  input_lra    = $MLRA"
echo "  input_thresh = $MTHRESH"
echo "  offset       = $OFFSET"

# Second pass: apply normalization
echo "Second pass $INPUT"
ffmpeg -y -i "$INPUT" -af loudnorm=I=$I:TP=$TP:LRA=$LRA:measured_I=$MI:measured_TP=$MTP:measured_LRA=$MLRA:measured_thresh=$MTHRESH:offset=$OFFSET:linear=true:print_format=summary "$OUTPUT"