sndfile-convert: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/sndfile-convert - from package: libsndfile

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/sndfile-convert - from package: sndfile-programs

You may install the required package with command apt-get install {package}

Error in other languages:
sndfile-convert: bevel nie gevind nie
sndfile-convert: comandă negăsită
sndfile-convert: comando não encontrado
sndfile-convert: commande introuvable
sndfile-convert: command not found
sndfile-convert: käsku ei ole
sndfile-convert: không tìm thấy lệnh
sndfile-convert: komanda nerasta
sndfile-convert: Kommando nicht gefunden.
sndfile-convert: kommandot finns inte
sndfile-convert: komut yok
sndfile-convert: nie znaleziono polecenia
sndfile-convert: níor aimsíodh an t-ordú
sndfile-convert: no se encontró la orden
sndfile-convert: no s'ha trobat l'ordre
sndfile-convert: opdracht niet gevonden
sndfile-convert: parancs nem található
sndfile-convert: perintah tidak ditemukan
sndfile-convert: príkaz nenájdený
sndfile-convert: příkaz nenalezen
sndfile-convert: команда не найдена
sndfile-convert: командата не е открита
sndfile-convert: 命令找不到
sndfile-convert: コマンドが見つかりません