SoX: Premature EOF on .wav input file

Question

I've got a bunch of WAV files and a script that copies them to another directory, but processes some of the files with SoX. The outputted files should all have 1 channel and have a sample rate of 44.1khz or less. Most of my files either have more than one channel or the sample rate is greater 44.1khz, but only 3 files have both. When converting those 3 files with the code snippet below, I get the "sox WARN wav: Premature EOF on .wav input file" error.

# $x is the filename + extension
# $2 is the destination folder
convertedWAV=false
hz=$(sox --info $PWD/$x | sed -n 4p | tr ' ' '\n' | tail -1)
chan=$(sox --info $PWD/$x | sed -n 3p | tr ' ' '\n' | tail -1)

# If its more than 44.1khz, then bring it down to that
if [[ $hz > 44100 ]]; then
    echo "ADJUSTING HZ"
    convertedWAV=true
    sox $PWD/$x --rate 44100 $2/$x
fi

# If its more than 1 channel (AKA Stereo), then reduce it.
if [[ $chan > 1 ]]; then
    echo "ADJUSTING CHANNELS"
    if [[  $convertedWAV == false ]]; then
        sox $PWD/$x --channels 1 $2/$x
    else
        sox $2/$x --channels 1 $2/$x
    fi
    convertedWAV=true
fi

if [[ $convertedWAV == false ]]; then
    ln "$PWD/$x" "$2"
fi

Notice how those 3 files went through two separate SoX commands. I then modified my script so if both channels > 1 and hz > 44100 then it does a single sox command, code seen below.

if [[ $chan > 1 ]] && [[ $hz > 44100 ]]; then
    sox $PWD/$x --channels 1 --rate 44100 $2/$x
elif [[ $chan > 1 ]]; then
    sox $PWD/$x --channels 1 $2/$x
elif [[ $hz > 44100 ]]; then
    sox $PWD/$x --rate 44100 $2/$x
else
    cp "$PWD/$x" "$2/$x"
fi

This now works. My question is, why? It behaves the same if I do sox $PWD/$x --rate 44100 --channels 1 $2/$x, for some reason doing it in two commands causes an issue. I can't find a definite answer. According to this the error can happen because the hdr's length isn't actually the length, so maybe the first SoX command corrupts the file slightly? I don't know if this is a bug with SoX's conversions or something wrong with my audio file/s. I've uploaded one of them here incase that helps.

Answer 1

sox $2/$x --channels 1 $2/$x

You can't concat the file $2/$x onto itself.