sig2fv: 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 Debian possible default full paths are:

/usr/bin/sig2fv - from package: speech-tools

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

Error in other languages:
sig2fv: bevel nie gevind nie
sig2fv: comandă negăsită
sig2fv: comando não encontrado
sig2fv: commande introuvable
sig2fv: command not found
sig2fv: käsku ei ole
sig2fv: không tìm thấy lệnh
sig2fv: komanda nerasta
sig2fv: Kommando nicht gefunden.
sig2fv: kommandot finns inte
sig2fv: komut yok
sig2fv: nie znaleziono polecenia
sig2fv: níor aimsíodh an t-ordú
sig2fv: no se encontró la orden
sig2fv: no s'ha trobat l'ordre
sig2fv: opdracht niet gevonden
sig2fv: parancs nem található
sig2fv: perintah tidak ditemukan
sig2fv: príkaz nenájdený
sig2fv: příkaz nenalezen
sig2fv: команда не найдена
sig2fv: командата не е открита
sig2fv: 命令找不到
sig2fv: コマンドが見つかりません