octiwhale · July 20, 2025 09:43
diff --git a/ev4_decode_f3.sh b/ev4_decode_f3.sh
 #!/usr/bin/env bash
 #
 # ev4_decode_f32.sh — Convert stereo to EV-4 quadraphonic WAV (32-bit float)
 #
 # Usage: ./ev4_decode_f32.sh input_stereo.wav [output_quad.wav]
 #
 # Description:
 # This script decodes a 2-channel (stereo) WAV file into a 4-channel WAV file 
 # simulating EV-4 (also known as Electro-Voice Stereo-4) quadraphonic sound.
 # The output format is 32-bit floating point PCM at 48kHz sample rate.
 #
 # History:
 # EV-4 (Electro-Voice Stereo-4) was one of the earliest matrix quadraphonic sound formats 
 # introduced in the early 1970s. It attempted to encode 4 discrete audio channels 
 # (Left Front, Right Front, Left Back, Right Back) into a standard 2-channel stereo 
 # signal for vinyl LP records. A decoder could then extract an approximation 
 # of the original four channels from the stereo mix.
 #
 # This script implements a simple EV-4-style matrix decoder using FFmpeg’s pan audio filter.
 # The decoding math is based on early matrix decoding formulas documented in quadraphonic 
 # audio literature, particularly "Four Channel Sound: A Guide" by Leonard Feldman and 
 # Marshall Buck (1974), which described how to simulate rear channels using 
 # phase-shifted or level-adjusted versions of the stereo channels.
 #
 # Channel Mapping in the EV-4 matrix:
 # - Front Left (FL)  = original Left channel
 # - Front Right (FR) = original Right channel
 # - Rear Left (RL)   = Left minus attenuated Right
 # - Rear Right (RR)  = Right minus attenuated Left
 #
 # The decoding matrix in this script follows the classic pattern:
 #   RL = L - 0.8*R
 #   RR = R - 0.8*L
 # The constant 0.8 is used as a balance between separation and natural blending.

 infile="$1"
 outfile="${2:-quad_output_f32.wav}"

 # Check if input file was provided
 if [[ -z "$infile" ]]; then
  echo "Usage: $0 input_stereo.wav [output_quad.wav]"
  exit 1
 fi

 # Run ffmpeg with pan filter to decode EV-4
 ffmpeg -y -i "$infile" \
  -af "pan=4c|c0=c0|c1=c1|c2=c0-0.8*c1|c3=-0.8*c0+c1" \
  -ar 48000 -ac 4 \
  -c:a pcm_f32le \
  "$outfile"
	#!/usr/bin/env bash
	#
	# ev4_decode_f32.sh — Convert stereo to EV-4 quadraphonic WAV (32-bit float)
	#
	# Usage: ./ev4_decode_f32.sh input_stereo.wav [output_quad.wav]
	#
	# Description:
	# This script decodes a 2-channel (stereo) WAV file into a 4-channel WAV file
	# simulating EV-4 (also known as Electro-Voice Stereo-4) quadraphonic sound.
	# The output format is 32-bit floating point PCM at 48kHz sample rate.
	#
	# History:
	# EV-4 (Electro-Voice Stereo-4) was one of the earliest matrix quadraphonic sound formats
	# introduced in the early 1970s. It attempted to encode 4 discrete audio channels
	# (Left Front, Right Front, Left Back, Right Back) into a standard 2-channel stereo
	# signal for vinyl LP records. A decoder could then extract an approximation
	# of the original four channels from the stereo mix.
	#
	# This script implements a simple EV-4-style matrix decoder using FFmpeg’s pan audio filter.
	# The decoding math is based on early matrix decoding formulas documented in quadraphonic
	# audio literature, particularly "Four Channel Sound: A Guide" by Leonard Feldman and
	# Marshall Buck (1974), which described how to simulate rear channels using
	# phase-shifted or level-adjusted versions of the stereo channels.
	#
	# Channel Mapping in the EV-4 matrix:
	# - Front Left (FL) = original Left channel
	# - Front Right (FR) = original Right channel
	# - Rear Left (RL) = Left minus attenuated Right
	# - Rear Right (RR) = Right minus attenuated Left
	#
	# The decoding matrix in this script follows the classic pattern:
	# RL = L - 0.8*R
	# RR = R - 0.8*L
	# The constant 0.8 is used as a balance between separation and natural blending.

	infile="$1"
	outfile="${2:-quad_output_f32.wav}"

	# Check if input file was provided
	if [[ -z "$infile" ]]; then
	echo "Usage: $0 input_stereo.wav [output_quad.wav]"
	exit 1
	fi

	# Run ffmpeg with pan filter to decode EV-4
	ffmpeg -y -i "$infile" \
	-af "pan=4c\|c0=c0\|c1=c1\|c2=c0-0.8c1\|c3=-0.8c0+c1" \
	-ar 48000 -ac 4 \
	-c:a pcm_f32le \
	"$outfile"
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